Vitamin D Deficiency in India: Prevalence, Causalities and Interventions

Vitamin D deficiency prevails in epidemic proportions all over the Indian subcontinent, with a prevalence of 70%–100% in the general population. In India, widely consumed food items such as dairy products are rarely fortified with vitamin D. Indian socioreligious and cultural practices do not facilitate adequate sun exposure, thereby negating potential benefits of plentiful sunshine. Consequently, subclinical vitamin D deficiency is highly prevalent in both urban and rural settings, and across all socioeconomic and geographic strata. Vitamin D deficiency is likely to play an important role in the very high prevalence of rickets, osteoporosis, cardiovascular diseases, diabetes, cancer and infections such as tuberculosis in India. Fortification of staple foods with vitamin D is the most viable population based strategy to achieve vitamin D sufficiency. Unfortunately, even in advanced countries like USA and Canada, food fortification strategies with vitamin D have been only partially effective and have largely failed to attain vitamin D sufficiency. This article reviews the status of vitamin D nutrition in the Indian subcontinent and also the underlying causes for this epidemic. Implementation of population based educational and interventional strategies to combat this scourge require recognition of vitamin D deficiency as a public health problem by the governing bodies so that healthcare funds can be allocated appropriately.


Introduction
Vitamin D deficiency is pandemic, yet it is the most under-diagnosed and under-treated nutritional deficiency in the world [1][2][3]. Vitamin D deficiency is widespread in individuals irrespective of their age, gender, race and geography. Vitamin D is photosynthesized in the skin on exposure to UVB rays. Sun exposure alone ought to suffice for vitamin D sufficiency. However, vitamin D deficiency is widely prevalent despite plentiful sunshine even in tropical countries like India.
Vitamin D deficiency has a bearing not only on skeletal but also on extraskeletal diseases. Owing to its multifarious implications on health, the epidemic of vitamin D deficiency in India is likely to significantly contribute to the enormous burden on the healthcare system of India. Cultural and social taboos often dictate lifestyle patterns such as clothing-that may limit sun exposure and vegetarianism-which certainly limits vitamin D rich dietary options. Most Indians are vegetarians. The socioeconomically backward people constitute a large percentage of the population in India. The underprivileged generally suffer from overall poor nutrition. Vitamin D rich dietary sources are limited and unaffordable to most Indians. Vitamin D supplements are available, but most Indians are not aware that they need additional vitamin D. Additionally, the cost of these supplements is essentially prohibitive to the majority. Fortification of staple foods with vitamin D may prove to be a more viable solution towards attaining vitamin D sufficiency in India.
There are scores of research papers in the literature reporting poor vitamin D status from all over India and some from other countries of the Indian subcontinent too. These research papers have been included in this review. Many of these studies measured serum 25-hydroxyvitamin D levels in ostensibly healthy subjects. Biochemical evidences of suboptimal bone health are elevated alkaline phosphatase (ALP) and elevated PTH levels (secondary hyperparathyroidism or SHPT). These were often reported in research papers, especially with respect to their correlation with vitamin D status. However, the most accurate and convincing measure of bone mineral density (BMD) is DEXA (Dual Energy X-ray Absorptiometry). Research articles reporting BMD, as measured by DEXA, in the context of vitamin D status of ostensibly healthy individuals, are few. BMD data, as they correlated with the vitamin D status in ostensibly healthy Indians is compiled. A few articles also reported results of interventions studies such as vitamin D supplementation and vitamin D fortified foods.
The aim of the paper is to impress upon the practicing physicians in India about the gravity of the vitamin D deficiency problem throughout India, so that they may take necessary caution and care in the diagnosis and treatment of vitamin D deficiency. Additionally, this article may also serve to make the case to the Health ministry, and the Food and Nutrition Board in India for population based strategy of fortification of staple foods with vitamin D. This paper provides a comprehensive picture of the vitamin D status of ostensibly healthy Indians, countrywide. The most reliable marker of vitamin D status is the serum concentration of 25(OH)D. In the publications, investigators reported their data on 25(OH)D levels either as nM (nanomoles per liter) or ng/mL. To simplify information and for the ease of comparison, in this review all the data on 25(OH)D levels are presented in a single concentration unit for serum 25(OH)D levels-ng/mL. Most investigators have used different cut-off levels to define vitamin D deficiency, insufficiency and sufficiency levels. While some may have done so due to preference perhaps, other investigators defined their own cut-off levels as determined by the linear regression between 25(OH)D levels and PTH levels. Therefore, to further facilitate comparison, in this review vitamin D deficiency is defined as 25(OH)D < 20 ng/mL, insufficiency as 20-29 ng/mL and sufficiency as ≥30 ng/mL. The data compiled here are also stratified by geographic locale of the study subjects, to press home the fact that vitamin D deficiency is widespread throughout the nation, irrespective of diverse dietary and social practices. For instance, despite fish being a staple diet in Bengal (eastern India) vitamin D nutrition is no better than in other regions. Geographical stratification of data also indicates regions of the country from where more data is needed. The effectiveness or failure of vitamin D supplementation and food fortification in restoring vitamin D levels and bone health have been reviewed, while making the case that vitamin D deficiency needs to be recognized as a public health problem. This review also discusses the need and feasibility of fortification of staple foods with vitamin D in India. Steps to be taken by the policymakers in India are also mentioned. Data, when available, from other countries of the Indian subcontinent are also compiled and presented for comparison.

Vitamin D Metabolism
Vitamin D can be synthesized in sufficient amounts by most vertebrates on adequate exposure of the skin to sunlight (UVB rays). It is critical that most vertebrates obtain a sufficient amount of vitamin D either from their diet or from adequate exposure of the skin to sunlight. The term "vitamin D" refers to compounds vitamin D 3 (cholecalciferol) or vitamin D 2 (ergocalciferol). Vitamin D 3 is produced in the skin on exposure to sunlight. Vitamin D 3 is derived from 7-dehydrocholesterol by ultraviolet irradiation of the skin. Vitamin D 3 is also found in animal food sources e.g., fatty fish (e.g., salmon, mackerel and tuna) cod liver oil, milk, etc. Vitamin D 2 is found in vegetal sources like sun-exposed yeast and mushrooms. Notably, most dietary sources are not sufficiently rich in their vitamin D content.
Vitamin D (both forms D 3 or D 2 ) is a prohormone which requires two hydroxylations to finally attain its biologically active form-1,25(OH) 2 D. The first hydroxylation occurs in the liver, at position C25 to form 25-hydroxyvitamin D, also known as 25(OH)D or calcidiol. 25(OH)D is the major circulating form of vitamin D. The second hydroxylation occurs at position C1α to form 1,25(OH) 2 D, also known as calcitriol. 1,25(OH) 2 D is produced primarily but not exclusively in the kidneys. 1,25(OH) 2 D is released in blood, where it binds to vitamin D binding protein (DBP) and reaches its target tissues to exert its endocrine functions through the vitamin D receptor (VDR). 1,25(OH) 2 D is also produced in several extrarenal tissues for its paracrine and autocrine functions. Most cells in the body have VDR. Many cell types can also produce 1,25(OH) 2 D. 1,25(OH) 2 D is capable of regulating a wide variety of genes that have important functions in regulating cell growth and differentiation.

Vitamin D and Skeletal Health
Rickets, osteomalacia and osteoporosis are widely prevalent all over the world. The most well recognized function of 1,25(OH) 2 D involves regulation of calcium and phosphorus balance for bone mineralization and remodeling. Without adequate levels of 1,25(OH) 2 D in the bloodstream, dietary calcium cannot be absorbed. Low calcium levels lead to an increase in serum PTH concentration, which leads to increased tubular reclamation of calcium in kidneys and resorption from the skeleton at the cost of lowering bone density. In the long term this leads to weakened and brittle bones that break easily. Approximately 40%-60% of total skeletal mass at maturity is accumulated during childhood and adolescence. Rickets results from inadequate mineralization of growing bone. Thus it is a childhood disease and it is manifested as bone deformities, bone pain and weakness. Biochemical abnormalities consistently include hypophosphatemia, elevated alkaline phophatase levels and serum 25(OH)D levels are usually below 5 ng/mL. Chronic vitamin D deficiency in adults results in osteomalacia, osteoporosis, muscle weakness and increased risk of falls [4][5][6][7][8][9][10][11]. Epidemiological support for skeketal benefits of vitamin D is well known [5,6,[12][13][14].

Vitamin D: Extraskeletal Effects
Biochemical studies have implicated vitamin D deficiency in many chronic diseases including, but not limited to, infectious diseases, autoimmune diseases, cardiovascular diseases, diabetes and cancer. Numerous epidemiological publications support the extraskeletal benefits of vitamin D and they cannot be ignored even though majority of these are association studies or small randomized controlled trials. Nevertheless, stronger evidence is required with the aid of more robust and reliable statistical methods such as randomized controlled trials (RCTs). These RCTs should be well-designed, well-executed and conducted worldwide to generate dependable and incontrovertible data, in order to assess the benefits of vitamin D supplementation not only as a preventive measure but also as adjuvant therapies [12,15,16].

Immunity
As early as in the 19th century, cod liver oil (a rich source of vitamin D) was used for treating tuberculosis (TB). Skin exposure to sunlight was an effective therapy for treating Mycobacterium infections of the skin. In 1903, Finsen received the Nobel Prize for demonstrating that Lupus vulgaris, the epidermal form of TB, could be cured using light from an electric arc lamp. In early 1900s, growing awareness of benefits of sun exposure pertaining treatment of infectious diseases led to the development of sanatoriums in "sun-rich areas". These sanatoriums enabled regimented sun exposure, diet and exercise. These sanatoriums primarily hosted TB patients [17]. Recent studies have linked vitamin D deficiency with increased risk of developing TB [18,19], otitis media [20], upper respiratory tract infections [21] and influenza [22].

Cardiovascular Health
Cardiovascular diseases (CVDs), including heart failure and coronary artery disease are a major cause of morbidity and mortality worldwide. There is accumulating epidemiological evidence from observational studies suggesting that CVDs are associated with vitamin D deficiency [23,24]. Increased risk of hypertension was associated with living at higher latitudes [25]. 25(OH)D level < 21 ng/mL was associated with increased risk of hypertension, diabetes, obesity and high triglyceride levels-all associated with increased cardiovascular mortality [26]. Various studies have reported reduced 25(OH)D concentrations in patients with previous and prevalent cardiovascular or cerebrovascular diseases [15,27].

Type 1 Diabetes
Type 1 diabetes (T1D) is caused by autoimmune destruction of pancreatic β cells, which eventually leads to insulin-dependent diabetes. Higher rates of incidence of T1D were observed at higher latitudes worldwide [28,29]. Epidemiological association of vitamin D intake and reduced risk of T1D was also seen [30]. A meta-analysis of observational studies showed a 30% reduction in risk of T1D in children receiving vitamin D supplements [31].

Type 2 Diabetes
Type 2 diabetes (T2D) is marked by insulin resistance (IR). In IR insulin is adequately or overproduced by pancreatic β cells, but is ineffectively utilized by the target cells of adipose, hepatic and skeletal muscles tissues. As a response to hyperglycemia, β cells further increase insulin production leading to hyperinsulinemia, which is often indicative of a pre-(T2D) stage. Hyperinsulinemia is associated with hypertension, obesity, dyslipidemia, and glucose intolerance [32]. These conditions are collectively known as "metabolic syndrome" [33]. A meta-analysis of observational studies showed inverse relation of 25(OH)D levels and calcium status with insulin resistance and hyperglycemia. In this meta-analysis, supplementation with both the nutrients combined showed benefit in optimizing glucose levels [34].

Serum 25(OH)D Levels as Indicative of Vitamin D Deficiency, Insufficiency or Sufficiency
Maintenance of adequate levels of serum 25(OH)D is essential to sustain the claimed pleiotropic effects, whether skeletal (classical) or extra-skeletal (non-classical). The threshold levels of serum 25(OH)D required to optimize its effects may not be the same in the various target organs. Based on classical skeletal effects, vitamin D deficiency is defined as serum levels of 25(OH)D < 20 ng/mL (50 nmol/L) with consequent and consistent elevation of PTH and reduction in intestinal calcium absorption. Vitamin D insufficiency is defined as serum 25(OH)D levels in the range of 20-29 ng/mL. At serum 25(OH)D levels of 30 ng/mL intestinal calcium absorption reaches its peak, and PTH levels continue to fall until this level of 25(OH)D is attained. Thus, vitamin D sufficiency is defined as serum levels of 25(OH)D 30-32 ng/mL. A desirable and safe range of serum 25(OH)D levels would be 30-100 ng/mL. This range would be sufficient for most known effects of vitamin D and also significantly lower to obviate concerns pertaining vitamin D toxicity.

Vitamin D Supplements and Efficacy Concerns
Commercially, vitamin D 2 is manufactured by ultraviolet irradiation of ergosterol from yeast. Vitamin D 3 is produced by the ultraviolet irradiation of 7-dehydrocholesterol from lanolin. Both forms of vitamin D are available as vitamin D supplements. Several other forms of vitamin D supplements are also available. 1,25(OH) 2 D is indicated specifically for patients with renal diseases and 25(OH)D is useful when hepatic hydroxylation of vitamin D is impaired.
Whether D 2 or D 3 , is more efficacious in raising and sustaining serum 25(OH)D levels, remains controversial. Several studies have proved equivalence between the two forms [46][47][48][49]. However, other studies reported that D 3 is more effective than D 2 in achieving and maintaining higher serum 25(OH)D levels [50][51][52][53]. Nevertheless, on a long term basis either form may be used, bearing in mind the long half-life (2-3 weeks) of 25(OH)D in circulation.

Testing Vitamin D Status
Plasma 25(OH)D or calcidiol (a summation of D 3 and D 2 forms) is the most reliable marker of vitamin D status. Immunoassays such as radioimmunoassay (RIA), enzyme linked immunosorbant assay (ELISA), chemiluminescence immunoassay and protein binding assays are used in routine testing of 25(OH)D in clinical laboratories. LCTMS (liquid chromatography tandem mass spectrometry) is the widely accepted reference method for 25(OH)D measurement. However, LCTMS is tedious, expensive and time consuming and therefore seldom used commercially.
Since vitamin D undernutrition is largely silent and subclincal, the indication for testing remains controversial. At present 25(OH)D test is the "most ordered test" in the USA. A similar trend has just begun in the upper socioeconomic stratum in India too. This clearly shows increasing awareness pertaining widespread prevalence of vitamin D deficiency among Indian clinicians. A 25(OH)D test using antibody based technologies in India costs an individual approximately INR 1500, which is unaffordable for most Indians. Surely, vitamin D status needs to be improved in most individuals in India and not just the privileged or a select few. However, testing every individual's vitamin D levels, in a population with such a high prevalence of vitamin D deficiency is not economically and practically feasible. Furthermore, whether subclinical vitamin D deficiency in otherwise healthy individuals should be treated or not, and to what target level of serum 25(OH)D remains controversial. It will be more cost-effective to implement aggressive nationwide vitamin D supplementation and food fortification programs for the benefit of all ostensibly healthy individuals.

Vitamin D Status of Ostensibly Healthy Indians
Countrywide studies (Table 1) have reported vitamin D deficiency in as high as 70%-100% of ostensibly healthy individuals. High prevalence of vitamin D deficiency was reported from northern to southern and western to eastern India, in ostensibly healthy children, adolescents, young adults and those ≥50 years old. All over India, vitamin D deficiency was highly prevalent in pregnant women and lactating mothers. Vitamin D status of these mothers correlated well with their neonates and their exclusively breastfed infants. Subjects from rural and urban areas presented a similar picture. Relatively, fish are a rich source of vitamin D. The residents of Bengal (eastern India) eat more fish compared to the rest of the Indians. Surprisingly, their vitamin D status appears to be just as poor as in the rest of the country [54]. Similarly, even healthy young soldiers with sufficient intake of calcium, adequate sun exposure and regular exercise regimen were found to be vitamin D deficient [55,56], as were young sportswomen [57]. Among resident doctors from Mumbai (western India) [58] and also doctors from eastern India [54], most were vitamin D deficient. Vitamin D deficiency was also observed in most of 2119 healthcare professionals studied from all over India [59]. Evidently, countrywide prevalence of vitamin D deficiency is undeniable.

Correlation of Vitamin D Status with Bone Health of Ostensibly Healthy Adolescents and Adults in India
Among otherwise healthy adolescents and adults studied, along with low serum 25(OH)D levels, a significant number of subjects also revealed other biochemical and clinical manifestations of vitamin D deficiency. Biochemical evidences of suboptimal bone health are: elevated alkaline phosphatase, a surrogate marker for increased bone turnover, and elevated PTH levels (secondary hyperparathyroidism or SHPT). ALP and PTH were often reported in research papers, especially with respect to their correlation with vitamin D status. However, the most accurate and convincing evidence of bone density is DEXA. Only research articles reporting BMD, as measured by DEXA, in the context of vitamin D status of ostensibly healthy individuals are included in this section ( Table 2). Vitamin D intervention studies that measured resultant BMD outcomes are discussed later in section 15 of this review.
Most studies did not show any correlation of BMD with vitamin D status. Notably, among 90 adults, who were 20-30 year-old soldiers from Indian paramilitary forces, with adequate nutrition, sun exposure and physical exercise, BMD was lower when compared to Caucasians. Among men, osteopenia was noted in 50% at the lumbar spine, 35% at the hip, and 50% at the forearm. Additionally, 10% of men had osteoporosis of the lumbar spine. Among women, osteopenia was noted in 32% at the lumbar spine, 14% at the hip and 21% at the forearm. The authors speculated that the effect of childhood malnutrition may have contributed to lower peak bone mass accumulation in these subjects [56]. BMD studies emphatically underline the need for adequate nutrition, sun exposure and physical exercise from the very beginning of one's life, to attain peak bone mass, and later to maintain it. Indubitably, vitamin D status in India is grim and needs to be reckoned with.

Vitamin D Sufficiency via Sun Exposure Is Not a Tenable Solution for Most Indians
Vitamin D deficiency is a major health concern in India, notwithstanding the brightly shining sun. The "adequacy of exposure to sunlight of an individual's bare skin" required to photosynthesize vitamin D is grossly ill understood. Darker skin has high melanin content which acts as a natural sunscreen. Therefore, darker skin produces a significantly lesser amount of vitamin D when compared with the individuals with fairer skin, such as Caucasians [60][61][62]. Thus, for Indian skin tone, minimum "direct sun exposure" required daily is more than 45 min to bare face, arms and legs to sun's UV rays (wavelength 290-310 nm). With the exception of those who perforce need to work outdoors in the sun, most Indians do not get adequate sun exposure to produce sufficient amounts of vitamin D endogenously. Indian social and or religious norms related to public modesty dictate that most parts of an individual's body, irrespective of gender, be covered. The not so D-lightful price of urbanization -in big cities a majority of people live in very high population density areas. They perforce live in overcrowded tenements, which are closely packed and 3-4 stories high. Consequently, direct sunlight does not reach inside most parts of the dwellings, thereby disallowing any sun exposure to an individual in the privacy of one's home. Additionally, lack of space offers limited options for outdoor activities. Atmospheric pollution of metropolitan India also factors in with respect to vitamin D status [63]. Use of sunscreen creams and umbrellas do not help either. The extreme discomfort of the scorching heat associated with most sunny days of Indian summer and (not to mention) the undying desire of most Indians to attain a fairer skin complexion instantly extinguish any desire for sun exposure, and a person's primary focus is on finding ways to avoid the sun, at all costs. In the blazing heat of India these two concerns score very high and the quest for vitamin D sufficiency takes a backseat, always. Therefore, in the Indian scenario, vitamin D sufficiency cannot be attained by depending on adequate sun exposure.

Nutritional Factors Attributing to High Prevalence of Vitamin D Deficiency in India
Vitamin D sufficiency by dietary intake is the only tenable solution for Indians. However, this solution itself has a barrage of problems.
• Most dietary sources of vitamin D have very low vitamin D content. Most of the food items rich in vitamin D are of animal origin. Most Indians are vegetarians. Commonly, a dietary source of vitamin D for vegetarians is milk, provided milk has been fortified with vitamin D. Milk is rarely fortified with vitamin D in India. The vitamin D content of unfortified milk is very low (2 IU/100 mL). Additionally, milk and milk products are unaffordable to the socioeconomically underprivileged. Another concern in India is the rampant dilution and/or adulteration of milk and milk products.
• Low calcium in Indian diet: Low dietary intake of calcium in conjunction with vitamin D insufficiency is associated with secondary hyperparathyroidism (SHPT). SHPT is further exacerbated by induced destruction of 25(OH)D and 1,25(OH) 2 D by 24 hydroxylase [64]. 24 hydroxylase is the key enzyme of vitamin D catabolism and is regulated by 1,25(OH) 2 D, PTH and FGF23 (Fibroblast Growth Factor 23) levels. FGF23 is a phosphate regulator. High serum phosphate levels increase production of FGF23 in bone osteocytes via the action of 1,25(OH) 2 D. Subsequently, FGF23 reduces renal phosphate resorption, indirectly suppresses intestinal phosphate absorption and also suppresses PTH and 1,25(OH) 2 D synthesis. Overproduction of FGF23 can result in increased morbidity associated with vitamin D deficiency [65]. This regulatory mechanism may explain the low 25(OH)D levels in rural subjects on a high phytate and/or low calcium diet, despite plentiful sun exposure. Most studies reported calcium intake much lower than the RDA (Recommended Daily Allowance) defined by the Indian Council of Medical Research (ICMR). Only two studies reported adequate calcium intake. In both these publications the study subjects were paramilitary soldiers [55,56]. ICMR's RDA for calcium intake in India is lower than that of the western world.
• Calcium balance is a function of intake and excretion [66,67]. Even though the Indian diet is low in calcium content, it also has a lower protein content and therefore low endogenous acid production, which may reduce urinary calcium loss. Therefore, the amount of dietary calcium required to maintain calcium balance may be lower than for those in the Occident. The protein-induced alterations in calcium homeostasis (and possibly in bone mass) have been attributed to increments in endogenous acid production and net acid excretion due to the oxidation of the constituent sulfur containing amino acids. On the other hand, the high salt content of Indian diet is likely to increase urinary calcium excretion. A direct relation between high sodium intake and lower bone mass has been reported [68].
• Intake of caffeine from tea and coffee is very high in India. Most Indians consume milk as part of their tea or coffee. The proportion of milk is very low in these drinks. Thus calcium intake through these beverages is low. Vitamin D is stable during cooking. It is stable up to 200 °C. However, thermal stability of vitamin D is an inverse function of both temperature and time.
In India, milk is boiled for several minutes before consumption. Before the same lot of milk is consumed in entirety, it is subjected to two-three rounds of boiling. In India most of the times, beverages like tea and coffee are boiled for several minutes to get the right flavor. This boiling may reduce the content of any vitamin D that there may have been left after boiling of the milk itself. Therefore, these beverages may not contribute significantly to either calcium or vitamin D intake in Indians. Vitamin D is a fairly robust vitamin. The preceding statements about its thermal degradation have been made as precautionary stance to not overstate the thermal robustness of this micronutrient. Additionally, studies have reported association of high caffeine intake with increased risk of low bone mineral density, osteoporosis, and osteoporotic fractures in middle-aged women. This situation is exacerbated in women with low calcium intake, especially in lean subjects [69].
• High prevalence of lactose intolerance in India is a major deterrent pertaining milk consumption, further lowering intake of calcium and vitamin D in these individuals. Ethnic and geographic variations of lactose intolerance were observed, with a higher prevalence in southern (Dravidian descent) and eastern India compared to northern India (Aryan descent) [70][71][72][73].
• Indian diet has high phytate content. Phytate is the principal storage form of phosphorus in many plant tissues, especially the bran portion of grains and other seeds. Phytate is indigestible to humans. Phytates chelate micronutrients such as calcium and iron, and thus reduce intestinal absorption of these nutrients. Benefits of sun exposure in rural subjects owing to an agrarian life were seen by significantly higher 25(OH)D levels [74]. However, possibly owing to high phytate content in diet, these levels were still insufficient in most individuals. Possibly, high phytate content in the diet of soldiers in northern India may have contributed to their vitamin D insufficiency, despite adequate sun exposure, nutrition and physical exercise [56].
• Notably, nearly all studies pertaining vitamin D status in healthy subjects reported a high phytate/calcium intake ratio. What Indians may require is a higher intake of calcium in their diet to lower the phytate/calcium intake ratio. Dietary habits in India have changed significantly. Many people remove a substantial proportion of bran from whole wheat flour before kneading to improve texture and fluffiness of chapatis (unleavened flat bread). Consumption of white bread is also very high. Most people prefer processed, split and polished pulses to whole seeds due to the ease of shorter time required for cooking and the consequent lowered expense of cooking fuel. Consumption of instant (or not) noodles and burgers also is on the rise across all socio-economic strata, with the exception of the impecunious.
• High phytate in Indian diet especially among the socio-economically lower classes stems from the elementary and immediate need of sufficiency of the calorific need. Cereals and legumes are more affordable and easily available than vegetables, milk and other dairy products. Besides, they are sources of protein for the vegetarians. Many cereals are also sources of calcium, however due to chelation by phytates its bioavailability is limited.
• In the scenario of inadequate calcium intake, vitamin D insufficiency and high phytate content in diet, environmental pollutants such as fluoride add insult to injury. Toxins like fluoride affect bone metabolism severely in the conjunction with inadequate calcium intake, especially in children [75,76].
• Cooking practices in India: Indians in general adhere to traditional cooking styles and practices, irrespective of their migration to any part of the world. In tropical climate perishable food items putrefy quickly. Notably, in India there is no perceptible government regulation on the hygiene and microbial quality control of fresh produce that reaches from the producer to the end-consumer. Consumption of uncooked fresh produce, especially vegetables, milk, etc., is generally considered ill-advised. As in the rest of the world, in India too, slow cooking is widely practiced. This culinary practice, however, is ill-advised bearing in mind the thermal instability of many vitamins. As mentioned earlier vitamin D is degraded at temperatures above 200 °C. Its thermal stability is inversely related to temperature and time. Cooking gas flame reaches temperature above 1900 °C and coal stove heat reaches 300-700 °C. Water boils at 100 °C. Baking is done mostly above 175 °C but the temperature in the food does not reach such high temperatures, therefore stability of vitamin D during baking is well within acceptable range [77]. Pertaining shallow and deep-frying of food, most cooking fats and oils have smoke points above 180 °C. Shallow and deep frying of foods is very popular in India. When foods are fried, vitamin D in the food comes out into the cooking medium and is thermally degraded [78]. Pressure cooking temperatures vary depending on the pressure withstood by the cooker used and may range from 100 °C to 120 °C. Short-time (as short as possible) pressure cooking is definitely advisable to retain at least some of the thermally more stable essential nutrients in cooked food, including vitamin D.
• Protein malnutrition and poor overall nutrition resulting from poverty: Perforce, in the sordid context of poverty, focus on a balanced diet is always on the back burner. It is very convenient to attribute dietary patterns or cooking traditions, than face a reality as grim as poverty. Factually, balanced diet is only an occasional treat to the impecunious. An old adage, "When a poor man eats chicken, one of them is sick", says it all.
• Publications indicating wide prevalence of vitamin D deficiency in healthy Indians have studied subjects mostly from lower and upper middle classes. Individuals below poverty line were not represented well in these studies. Hence, poor nutrition observed in these studies may also stem from lack of awareness of the features, benefits and necessity of balanced nutrition.       Comparatively, postmenopausal women had lower BMD in forearm, hip and lumbar spine. Osteoporosis was seen at hip (15% and 28%), forearm (0% and 11%), lumbar spine antero-posterior (6% and 22%) and lumbar spine lateral (0% and 23%) among premenopausal and postmenopausal, respectively.

Genetic and Epigenetic Factors Affecting Vitamin D Status
Genetic factors leading to vitamin D deficiency in Indians, due to their effect on expression of genes that modulate vitamin D metabolism may not be ruled out. Genetic factors such as polymorphisms in 7 dehydroxylase reductase, DBP, 1 alpha hydroxylase, VDR, 25 hydroxylase, 24 hydroxylase have been studied. However, a clear association between these polymorphisms and vitamin D status is yet to be established [113][114][115]. Epigenetic factors too may be important in this context. Epigenetic factors pertain to heritable changes in the gene expression, while the DNA sequence is unchanged. These are several possibilities-post-translational modifications of histones-methylation, acetylation and phosphorylation, and also aberrant expression of microRNAs. Interaction between genetic and environmental factors, modulated by epigenetic factors has been reported. 1α hydroxylase and 24 hydroxylase have been shown to be epigenetically controlled. Information regarding association between genetic and/or epigenetic factors and vitamin D status is inconclusive and warrants further study [116].

Population Based Approaches to Improve Vitamin D Status in India: Supplementation, Food Fortification and Educational Programs
There is protracted debate ongoing on issues pertaining optimal levels of intake of vitamin D, preferred form of vitamin D for human use and extraskeletal benefits of vitamin D. However, one thing is clear-Indians need more vitamin D. Vitamin D can be obtained from three sources: sun exposure (limitations of which has been discussed earlier), vitamin D supplements and vitamin D fortified foods. There is urgent need to prioritize development of national level programs to make available, quality-regulated and affordable vitamin D supplements and vitamin D fortified foods to the Indian populace. Very importantly, the government needs to implement measures to educate the Indian populace about the current status of vitamin D in India and also the modes to attain vitamin D sufficiency.

Vitamin D Supplements Available in India
Information was collected from 10 pharmacists, from an upper middleclass locality of Delhi. Supplements commonly available are-D 3 (cholecalciferol), 1,25(OH) 2 D 3 and 1 alpha hydroxy vitamin D 3 (alfacalcidol). Some formulations have calcium too. Multivitamin formulations are also available and contain about 400 IU of D 3 . None of the pharmacists had heard of D 2 supplements. D 3 supplement of 60,000 IU is the highest selling one and is available in powder form in sachets or as oil-based capsules. Recommended dose on the label is once per week. The sachets indicate that half a sachet per week may also be taken. According to some pharmacists, many clinicians recommended 1 sachet daily for 10 days, followed by 1 sachet/week for 5-6 weeks to 1 sachet/week forever. The other vitamin D supplements mentioned here are present in lower doses (0.25 µg or 500 IU) and daily intake (1-4 times/day) may be recommended by the clinicians. Calcium supplementation is generally recommended with vitamin D intake.
The cost of a single dose of 60,000 IU of vitamin D 3 is about INR 30. Intake of 60,000 IU of vitamin D 3 per week may be advisable for a short duration, for patients with severe vitamin D deficiency, but a regular weekly dose may be lead to toxicity problems. A lower dose of vitamin D not exceeding the limit of 4000 IU per day would be advisable for otherwise healthy individuals. This will also reduce the cost of the supplement and become more affordable to the common people of India.
Purchase of most drugs in India does not require a prescription. Additionally, more often than not pharmacists (commonly called "Chemists" in India) often claim to have all the information needed to prescribe medicines. Other than for acute health problems most socioeconomically backward people go directly to the pharmacist, more often than not, in order to save consultation fee of a licensed clinician. Pharmacists boldly recommended and sell medications to patients and often recommend a longer duration of medications to boost their sales. It is not uncommon for active vitamin D analogs such as calcitriol or 1-alpha D to be wrongfully prescribed by physicians and pharmacists in lieu of nutritional vitamin D supplements, thus putting unsuspecting patients at grave risk of hypercalcemia and if taken long-term possibly vascular calcification and kidney stones. In this context, it is very important that the along with the clinicians, pharmacists also be educated about toxicity issued related with vitamin D.

Vitamin D Supplementation Studies in Ostensibly Healthy Indians
Vitamin D supplementation studies in ostensibly healthy were compiled (Table 3). Supplementation resulted in significant improvement in vitamin D status, but a large proportion of the population had still did not attain sufficiency. The following study is noteworthy. In India, physicians often prescribe D 3 60,000 IU per week for 8 weeks for vitamin D deficiency. Twenty two healthy Indians with subnormal serum 25(OH)D levels were supplemented with oral D 3 60,000 IU/week and calcium 1 gm/day for 8 weeks. At 8 weeks the mean 25(OH)D levels increased from 10.16 (3.96) ng/mL to 22.4 (6.8) ng/mL and serum PTH normalized in all. Twenty two of the 23 subjects had 25(OH)D levels > 20 ng/mL. At the end of 12 months however, all the subjects were vitamin D deficient, once again. To sustain optimal 25(OH)D levels vitamin D supplementation would need to be ongoing after the initial loading [117].
Some supplementation studies, in ostensibly healthy adolescents and adult subjects, resulted in improved bone health. These are tabulated separately (Table 4).
More frequent and lower doses, not exceeding 4000 IU/day of vitamin D supplementation may be better for maintenance of serum 25(OH)D level. Most of the studies from India mention vitamin D status in terms serum 25(OH)D levels as below or above 20 ng/mL (or 50 nmol/L). However, one must not lose sight of the fact that the aim of all interventions in terms of vitamin D status should be ≥ 30 ng/mL or above to derive both skeletal and extraskeletal benefits of this D-lightful nutrient [118], but with a precautionary stance to not exceed 100 ng/mL.

Vitamin D Fortification in USA and Canada
Despite predominantly non-vegetarian dietary pattern, approximately 60% of the intake of vitamin D from food comes from fortified foods in USA [119] and Canada [120]. In USA, vitamin D fortification of foods is voluntary, but it is strictly regulated pertaining categories of foods, functional use and level of use, thus limiting over-fortification. Vitamin D fortified milk has been available in USA since the 1930s. Vitamin D is added to most milk sold in the United States, although it is not added to all milk products like cheese and ice cream. Some manufacturers also add it to cereal, soy milk, rice milk, and orange juice, usually along with calcium. In USA either form, D 2 or D 3 , may be used for fortification, but commonly D 3 is used. In Canada, the law mandates fortification of milk, milk alternatives and margarine. Similar to USA, for other permitted foods, vitamin D fortification D is voluntary, but fortification level is limited [121].

Need for Vitamin D Fortified Food Products in India
Vitamin D sufficiency via sun exposure is untenable for most Indians, as discussed earlier. Vitamin D (relatively) rich dietary sources are unaffordable and mostly limited, especially for vegetarians. Most Indians are vegetarians. Vitamin D supplements are unaffordable and not feasible as a population based approach. Fortification of widely consumed staple foods with vitamin D is the only viable solution towards attaining vitamin D deficiency in India. Unlike supplementation strategies, fortification of food with vitamin D poses a negligible risk of toxicity.

Feasibility of Fortification of Foods with Vitamin D in India
Food fortification is a much more economically viable approach compared to vitamin D supplementation. While the cost of fortified food items will be more than unfortified foods, it will be lower than supplementation.
1. Adaptability to fortified food by the consumers is much better than to supplementation. Food fortification requires relatively less change in food habits and preferences, leading to better efficacy of fortification programs, lowered cost to the consumer and a larger profit to the food manufacturers. Clearly a win-win partnership for all. 2. Food fortification may be a better choice compared to supplementation strategies, especially when targeting those who need it the most-women (including non-pregnant, pregnant and lactating), infants, children (especially girls, who are sidelined, more often than not, in India) and senior citizens. 3. Use of staple foods such as chapati flour, rice, etc., for fortification may have certain advantages over other fortification matrices. Indian government offers cereals, chapati flour, rice, lentils, etc., at subsidized rates to the socioeconomically underprivileged citizens. Additionally, cost of these products is generally tightly regulated by the government. Thus, no large fluctuations are observed in the cost of these food items in the open market also. This will ensure continued consumption of these foods fortified with vitamin D, by those who avail of them and result in better and sustained economical feasibility of the fortification programs in the long run. 4. Two vitamin D fortification studies in ostensibly healthy subjects were reported in the literature (see Table 5). Underprivileged toddlers, fed with fortified laddoos, resulted in significant increase in serum calcium and vitamin D levels and also in total body less head (TBLH) bone mineral content (BMC) [122]. The cost of fortified laddoo was INR 20 per laddoo, which may be prohibitive in itself. More cost effective food items could be fortified with vitamin D.
In another study, 776 subjects (boys and girls) were given fortified milk, which resulted in significant improvement in their vitamin D status [123]. These results support the strategy of fortification of foods in India for redressing malnutrition problems in India. Table 3. Vitamin D supplementation studies in ostensibly healthy Indians. All 25(OH)D values have been shown in ng/mL. To convert from nM to ng/mL, nM values were divided by (2.5). Vitamin D deficiency is defined as 25(OH)D < 20 ng/mL, insufficiency as 20-29 ng/mL and sufficiency as ≥30 ng/mL. ‡ Information available from the abstract of the article. D 3 is cholecalciferol. Calcium amount mentioned is of elemental calcium. Age of the subjects is in mean age (SD) years, unless otherwise indicated.      Table 4. Vitamin D supplementation studies reporting improved bone health post-intervention, in ostensibly healthy Indians (adolescents and adults). All 25(OH)D values have been shown in ng/mL. To convert from nM to ng/mL, nM values were divided by (2.5). Vitamin D deficiency is defined as 25(OH)D < 20 ng/mL, insufficiency as 20-29 ng/mL and sufficiency as ≥30 ng/mL. D 3 is cholecalciferol and D 2 is ergocalciferol. Calcium amount mentioned is of elemental calcium. Age of the subjects is in mean age (SD) years, unless otherwise indicated. Mean increase in 25(OH)D was 19%, mean decrease in PTH was 9%. BMD showed no change. N = 25, Study group: 300,000 IU D 2 once every 3 months and 250 mg calcium/day for 1 year. Study group was divided into sub groups: (1) girls who had menarche within 2 years and (2) girls who had menarche for over 2 years, at the start of the study. Overall, 25(OH)D increased by 68% and PTH decreased by 27%. No significant changes were observed in subgroup (2). However, in subgroup (1) total bone mineral content (TB BMC) and total bone area (TB BA) increased and lumbar spine BMC was higher.

Locale Study Subjects and Supplementation
Pune (18.5°N) Urban, premenarchal schoolgirls, age 9.8 (1) years. All the girls were shorter and lighter compared to Indian norms. All subjects received 300,000 IU D 3 once every 3 months, for 1 year. 65  and whole dried Bengal gram (Cicer arietinum) 7.5 g each, sesame seeds (Sesamum indicum) and poppy seeds (Papaner somniferum) 5 g each, 5 g of clarified butter (Ghee) and 15 gm of refined palm sugar.

Food Items Which Could Be Fortified with Vitamin D in India
1. Milk: The whole array of different grades of milk available could be fortified-whole milk, toned, double toned and skim milk. 2. Milk curd and yogurt. 3. Infant formulas. 4. Butter, ghee (clarified butter) and oils, to use as spreads or to spike already cooked food. 5. Soy milk, soy curd (tofu), orange juice and mango juice may be fortified to cater to the needs of the lactose intolerant individuals and those who are allergic to milk proteins. Processed cheese also has very low lactose content and is rich in calcium and may be fortified for the benefit of the lactose intolerant. Due to high prevalence of dyslipidemia, metabolic syndrome and cardiovascular diseases in India, these fortified items will also offer healthier choices to the general population. 6. Widely consumed and affordable staple food items such as chapati flour, maida (all purpose wheat flour, used to make bread and other bakery products), rice and rice flour may be suitable vehicles for fortification strategies in the Indian scenario.

Foods Fortified with Vitamin D Available in the Indian Market
Vitamin D fortified milk from Amul ® (an Indian dairy cooperative, located in Anand, Gujarat, India) is the only fortified milk product found in the general market. It is 4.5% fat, homogenized milk fortified with calcium 150 mg, vitamin A 75 μg and vitamin D 0.5 μg (20 IU), etc., per 100 mL. The expiry date of this milk is 120 days if the carton is unopened. Incidentally, with a 10% or more loss per month at 4 °C, there is not much vitamin D left by 120 days. It may be hoped that storage temperatures are always adhered to. But in India this is a remote possibility due to economical and technical limitations. In a brief survey, most retailers reported that the Amul ® milk cartons supplied to them were generally one month past expiry date already at the time of delivery and that the demand for this product was very low. Cost per liter is INR 48 (as on 12 January 2013) as opposed to the cost of unfortified milk (INR 30).
Kellogg's breakfast cereals fortified with vitamin D along with other micronutrients are also available. However, the exorbitant prices of these products are essentially prohibitive for consumption by the common people of India.

Estimated Burden of Bone Diseases on Indian Healthcare System
There is no "national body" instituted by the government of India, to study and document the prevalence of bone diseases in India. The following figures pertaining bone health were perforce taken from research articles. In India, bone diseases such as rickets, osteomalacia and osteoporosis have been [67,[135][136][137] and still are widely prevalent and formidable problems of our nation. As per 2001 Census Report about 163 million people were above the age of 50 years. This figure will be much bigger from the 2011 Census Report and may exceed 200 million. About 15%-20% of persons above the age of 50 years would be developing osteoporosis [136]. As presented in this review, BMD studies of ostensibly healthy Indians show that a significant proportion of younger Indians too are suffering from this silent disease. As the early signs of osteoporosis are diagnosed with accuracy, BMD data will add to these already astounding figures. Some staggering figures and estimates pertaining rickets, osteomalacia and osteoporosis are mentioned in some reviews [136,137].
Vitamin D status in India is grim not only in the lower and but also in the upper socioeconomic classes. For the sake of simplicity and argument, let us consider only the skeletal benefits of vitamin D. Vitamin D sufficiency in women of reproductive age would at the very least result in -improved women's health, improved outcome of childbirth and birth of infants who may have a better chance of a healthy existence from the beginning of their lives. Vitamin D sufficiency in growing children would mean allowing for their full growth potential-physically, mentally and psychologically. In children, rickets translates into life-long deformity, osteomalacia-a painful and subpar existence. Osteoporosis is a silent disease tethered to a constant threat of fractures to the unbeknownst afflicted. In elderly patients, especially hip fractures result in the end of an independent existence. Notably, most people in India do not have health insurance. Hospitalization of patients with hip fractures is much longer than for those being treated for cancers. For those who cannot afford hospitalization for treatment, it is a long, agonizing and often an unending wait for resurrection. This fact indicates the heavy load on the healthcare system and the economy of the nation due to bone diseases alone.

Government's Intervention Required
Vitamin D sufficiency status may not be treated as a "feel good status" for the affluent who can afford medical expenses and expensive vitamin D supplements. Vitamin D is prevalent across all socioeconomic strata. It is imperative that policymakers understand the gravity of the situation pertaining vitamin D status and as a consequence-the untold burden on the healthcare system in India. The information presented in this article ought to persuade policymakers to take substantive measures towards attaining vitamin D sufficiency. Actions needed to be taken by the government of India are as follows: Political and administration's will and support should be available from the development stage of the fortification program and equally importantly sustained. 4.1 Involvement of the food industry by encouraging private enterprises operating at the national and local level is required. Support in terms of technical expertise pertaining production of fortified food items, availability of standardized vitamin D formulation(s) and information on the marketing potential of the fortified items should be made available. 4.2 Effective legislation to ensure good quality and regulated vitamin D fortified foods at minimal cost to the end consumer is required. That said, both the administration and legislature should very importantly be facilitative and not be restrictive or punitive to those who are striving towards attaining better bone and mineral health of the masses. 5 School going children could benefit from the following: 5.1 Educators should emphatically teach the need for vitamin D sufficiency and benefits of a healthy lifestyle. Inclusion of the benefits of vitamin D in the ken of the kids may perchance spread this information to their (unaware) kin too. 5.2 Mandatory distribution of vitamin D fortified foods at midday meals in schools. 5.3 Daily physical exercise should be made compulsory in schools. 6 Affordable and widely accessible testing facilities for vitamin D levels should be made available to individuals who are at high risk of clinical vitamin D deficiency. 7 Reliable and sensitive technology such as DEXA should be made available at minimal cost for screening bone mineral density in individuals at high risk, with easy accessibility, throughout India. 8 Last, but not the least, government should extend support to research groups, so that the impact of supplementation programs and fortification strategies in actual practice may be studied and monitored and more efficacious ways developed. Continued research and epidemiological studies are required, to clearly state the enormity of the vitamin D deficiency status and its implications on general health of Indians, countrywide. Vitamin D status from western, eastern, northeastern India and the Himalayan regions and are still either few or lacking. Also, the very poor and the marginalized citizens have not been included in such studies.

A Lagniappe for the Readers: Other Countries of the Indian Subcontinent Present a Similar Scenario Pertaining Vitamin D Status
Other countries of the Indian subcontinent: Pakistan, Bangladesh, Nepal, Sri Lanka, Myanmar and Bhutan share the same geographic locale and socioeconomic culture with India. Data were compiled from these countries too. Vitamin D deficiency is highly prevalent in these countries (Table 6). One report was available from Pakistan pertaining bone health of ostensibly healthy subjects. In a cohort of 140 rural postmenopausal women from Khazana (34.7° N) and Nahaqi (34.2° N), age 52(SD 2) years, 42% had osteopenia and 28% had osteoporosis. 25(OH)D levels correlated with BMD [138]. No reports were available from other countries of the Indian subcontinent pertaining vitamin D status and its correlation with BMD. One supplementation study from Bangladesh showed significant improvement in the vitamin D status (Table 7). One supplementation study from Pakistan showed significant improvement in the vitamin D status and improved bone health (Table 8). No food fortification studies were available from any of these countries. From the available data, it is clear that vitamin D scenario in these countries is similar to that in India. The data from other countries of the Indian subcontinent also show that though India may be economically more advanced that some of its neighbors, the vitamin D scenario is similar all over the subcontinent.

Conclusions
Widespread prevalence of vitamin D deficiency in India is undeniable. Factually, sun exposure is an untenable solution, for most individuals in India, towards attaining vitamin D sufficiency. Low calcium intake in conjunction with vitamin D deficiency makes matters worse. The need for improvement in vitamin status of the Indian population is both important and urgent. The Indian government needs to take substantive measures in this direction. Revision of RDA for calcium and vitamin D is required. Better facilities and technologies should be made available countrywide to enable timely diagnosis of clinical manifestations of vitamin D deficiency in individuals who need attention by the clinicians. Population-based programs at the national level must be developed to increase awareness of the problem at hand, to provide affordable vitamin D supplements and also to provide vitamin D fortified foods to the Indian populace at large. Research in this field needs continued support to provide a comprehensive picture of the ongoing vitamin D problem and also to study and monitor the effect(s) of a partnership between the government, healthcare system, industry and consumers, aimed at improving the vitamin D status in India. Table 6. Vitamin D status of ostensibly healthy subjects from other countries of the Indian subcontinent. All 25(OH)D values have been shown in ng/mL. To convert from nM to ng/mL, nM values were divided by (2.5). Vitamin D deficiency is defined as 25(OH)D < 20 ng/mL, insufficiency as 20-29 ng/mL and sufficiency as ≥30 ng/mL. Age of the subjects is in mean age (SD) years, unless otherwise indicated.    Table 8. Vitamin D supplementation studies reporting improved bone health post-intervention, in ostensibly healthy subjects from other countries of the Indian subcontinent: All 25(OH)D values have been shown in ng/mL. To convert from nM to ng/mL, nM values were divided by (2.5). Vitamin D deficiency is defined as 25(OH)D < 20 ng/mL, insufficiency as 20-29 ng/mL and sufficiency as ≥30 ng/mL. D3 is cholecalciferol. Calcium amount mentioned is that of elemental calcium. Ali 2013 [155] No pertinent reports with information required were available from Bangladesh, Nepal, Sri Lanka, Myanmar and Bhutan.