Osteoporosis is a systemic skeletal disease portrayed by low bone mass and structural weakening of the bone material that leads to reduced bone strength and increased susceptibility to fracture. Although all bones can be affected, the hip, vertebra and wrist bones are at high risk. Osteoporosis is commonly referred to as a “silent disease” as there are no symptoms until the fracture occurs [1].

Osteoporosis is a debilitating chronic disease that is a public health problem. It is estimated that 10 million individuals have osteoporosis while another 34 million suffer from low bone density. An estimated 61 million individuals will develop osteoporosis or low bone density by 2020 [1]. In 2002 annual direct care expenditures for osteoporotic fractures reached almost 18 billion dollars [2,3]. Beyond costs, there is the physical burden of living with osteoporosis and its impact on daily living, including restrictions in daily activities, loss of confidence (due to fear of falling and fracture) and loss of independence [4].

With people living longer, fracture risk is expected to increase. Each year an estimated 1.5 million individuals suffer a fracture due to bone disease. For those over 50 who suffer a hip fracture, approximately 4% will die in the hospital and 24% will die within the year. The risk of a fracture increases with age and is greatest in women. Approximately one in two women and one in four men aged 50 or older in the United States will experience an osteoporotic-related fracture sometime during the remainder of their lives. As people live longer, the lifetime risk of fractures will increase for all ethnic groups [2]. With the high costs of treating osteoporosis fractures [5], effective preventive interventions are needed.

Osteoporosis is primarily viewed as a woman’s disease. However, after age 50, 6% of all men will experience a hip fracture and 5% will have a vertebral fracture as a result of osteoporosis [1,2]. Bone loss occurs rapidly in women at menopause; for men the loss still occurs but later (in their late 60s and in their 70s). The topic of bone health and osteoporosis in men is not well studied, but it is believed to often occur due to secondary causes, such as corticosteroid therapy [6].

Risk factors for low bone density, osteoporosis and fractures, include both unchangeable and modifiable types of factors. Conditions increasing the chance for developing osteoporosis include: fracture history after age 50, family history, female gender, small bone frame, advanced age, estrogen deficiency, amenorrhea, low testosterone levels, some medications, certain chronic diseases, long-term low intake of calcium, vitamin D deficiency, inactivity, cigarette smoking and excessive alcohol [7]. Fortunately, there are many modifiable lifestyle factors (diet and activity) along with drug treatment which can prevent or slow the loss of bone.

The National Osteoporosis Foundation developed five steps to optimize bone health [1]. These include:

Clinical studies have reported increases in calcium intake as a result of calcium supplementation and physical activity and intense supervision [2,8,9]. There is an inverse relationship between physical activity and future hip fracture risk for both women and men [10,11]. Resistance exercise combined with aerobic weight-bearing activity has been shown to improve bone mineral density (BMD) in postmenopausal women without a history of fractures. Calcium and vitamin D supplementation have been shown to increase BMD, but even within clinical trials adherence to taking supplements is not optimal. In fact, one large trial found no change in BMD in women enrolled in the supplement arm of the trial. However, when only those who actually took the supplements on most days were analyzed a significant improvement in hip BMD was found [12]. Clearly, exercise and diet can have a positive impact on bone health.

These research studies could be placed into one of four groups: calcium and vitamin D from food (Table 1), calcium and vitamin D from supplements (Table 2), other bone health-related nutrients (Table 3) and portfolio diets (Table 4).

More than a decade ago the Food and Drug Administration approved the label health claim that calcium-rich products can lower the risk for osteoporosis [42]. Since that time, the relative importance of calcium in bone health and fracture prevention has been an issue of many investigations. A primary function of vitamin D is to maintain serum calcium and phosphorus levels within a constant range, and to enhance calcium availability by intestinal uptake and osteoclast activation. In the last five years, scientific interest in vitamin D has blossomed, both in regards to bone and other medical conditions. Clearly both calcium and vitamin D contribute to healthy bone maintenance during aging, although the relative contribution may still be unclear. Nevertheless, all osteoporosis medication recommends adequate intake of calcium and vitamin D to ensure optimal effectiveness of the drug.

As such, the results of this review are not initially surprising. One finding of this review is that most studies found that vitamin D supplementation would increase serum vitamin D levels [21,22] and an improvement in serum markers of bone health and/or PTH was reported [21,22,23,27]. In addition, BMD was improved with supplementation [23,24,25,26,29] and number of falls were reduced in some [29,30] but not all studies [28]. Our results concerning supplements are similar to other recently published reviews. A meta-analysis of vitamin D alone or vitamin D with calcium supplementation found that vitamin D with calcium was effective in reducing overall fracture risk and hip fracture risk [43]. Indeed this was also reported in a meta-analysis of calcium supplementation on hip fracture. Reid et al. reported that hip fracture risk was significantly increased with calcium supplementation alone, but decreased with both calcium and vitamin D supplementation [44]. This is in contrast to the meta‑analysis reported by Tang et al. in [45] in which calcium supplementation decreased fracture risk, and little was added to the reduction when vitamin D was added. However a Cochran review concluded that vitamin D alone was ineffective in preventing hip fracture in older people, and although vitamin D with calcium did appear to reduce hip fracture incidence, hypercalcaemia was more common in older persons taking vitamin D with or without calcium, with some increases in gastrointestinal symptoms and renal disease [46].

One interesting result of this analysis was that few reviews and no meta-analyses have evaluated food as the source of calcium and/or vitamin D, which are far less likely to produce side effects. Our review found that studies providing calcium as food sources increased calcium and vitamin D intake [15]. When calcium and vitamin D intake was increased, an effect was seen on BMD, bone turnover markers, and PTH [13,14,15]. It is more difficult to quantify calcium or vitamin D intake when these nutrients are eaten as foods rather than as supplements. While there are several validated instruments published for assessing calcium intake in various groups [47,48,49,50,51,52,53,54], very few include calcium-fortified foods [55]. A significant gap in the research includes not only a vitamin D instrument for intake documentation, but a database containing the expanding list of vitamin D-fortified foods.

Of interest is those educational interventions without a food or supplement also increase calcium intake [9,15,19]. Decades of research on nutrition education have found that education would be more effective if focused on specific behaviors and if appropriate theory was used for designing the intervention [56]. A study of older adults (n = 162) found that attitudes and perceived control were important predictors of dairy product intake, whereas subjective norms were not (those significant people who influence our behavior) [57]. Not surprisingly in our review, when the education lacked depth and theory, e.g., mailings to participants, no improvement in calcium intake was found [17]. More importantly, studies examining mediators of bone-related dietary change in older adults are lacking. Similar to demonstrating a physiological mechanism for how nutrients affect health, investigations into educational strategies must investigate how behavioral theories mediate dietary change [58].

Concerning protein, both high and low protein intakes have been shown to have negative effects on bone, with negative effects more pronounced with inadequate calcium intake than with adequate intake [59,60,61]. The study supported a positive effect of protein on bone health. Other studies distinguish between animal and vegetable protein [62], or the acid load of protein and its effects on bone health. A review of all the studies related to bone and protein intake is beyond the scope of this paper. However, an educational interventional approach to adequate calcium, vitamin D, and protein intake with older persons is clearly lacking in the literature. One study did show that protein supplementation offered no additional increase in muscle mass in middle age and older men involved in a resistance exercise randomized control trial [63]. This is mentioned to highlight the other pertinent aspects of bone health, namely muscle mass and exercise.

Other nutritional issues highlighted in our review included vitamin K, soy, and portfolio diets. The latter presents the most holistic approach to investigating the optimal diet for bone health in aging, and may also include exercise and fall prevention training. The studies highlighted in this review demonstrate that key lifestyle habits can be utilized to strengthen bone health and reduce fracture risk. As previously mentioned, the National Osteoporosis Foundation [1] developed five steps to optimize bone health, the first of which is to improve calcium and vitamin D intake. As shown in the present review, this can be accomplished with either food or supplements in older adults. Medications certainly have a role for treating osteoporosis. However, with the number of medications that the older person is prescribed continuing to rise, there is a need to consider less aggressive measures when possible.

While most intervention studies and reviews concerning bone health have included medication as the primary intervention, relatively few have concentrated on diet or supplements alone. Pharmacological approaches will have a significantly higher effect on BMD, and possibly on falls and fractures, but at the same time pose a higher risk for medication-associated side effects, especially if continued for decades.

Many nutrients play a role in optimizing skeletal mass. In addition to vitamin D and calcium, deficiency, and in some cases excesses, of other nutrients can impact bone mineral density. These nutrients are commonly obtained by following the U.S. Dietary Guidelines [54]. Interventions, including foods or supplements, or targeting behaviors, have shown positive results. Additional research is needed to examine the impact of educational strategies that combine all nutritional factors into one randomized controlled intervention; then further to examine the impact of education plus supplemental foods. The results of these trials will perhaps provide an effective strategy for bone health in aging adults who prefer not to take supplements or medication. Future research may also combine these proposed projects with balance, flexibility, and impact exercise, to determine their additional effects on bone density, fracture rates, and markers of bone health. With the economic factors of supplements and medication, as well as quality of life issues, additional research is needed to examine the potential role of education strategies concerning bone health in aging.

An inherent limitation in evaluating impact of interventions is publication bias. Significant changes are commonly needed in order to be published. If an intervention produced no change, this may not be published and consequently data were not available for review.

With the focus of the review being nutritional interventions, the review excluded studies that focused on drug treatment. These studies may have provided additional nutritional information but the diet variable is often held constant in these studies.