Fat-soluble vitamins are indispensable to ascertain optimum health in all life stages [1
]. Except for vitamin D, which is mainly produced under the influence of ultraviolet B (UVB) radiation on the skin, dietary intake is the main source for all vitamins. A well-balanced and healthy diet is therefore essential to prevent disease and reduce the burden of disease [2
Over the last few decades, diets in high income countries have shifted to more energy-dense and nutrient-poor diets, resulting in increasing prevalence of inadequate intake and suboptimal status of micronutrients [3
]. Inadequate intakes of vitamins A and D are a general concern in different populations and population subgroups in Europe [4
]. The reduction of the prevalence of micronutrient inadequacies should therefore be a priority in food and nutrition policies in Europe [6
]. Adequate intake of micronutrients can be achieved through health promotion, as well as through fortification and supplementation practices [1
]. In the USA, fortified foods and/or supplements contribute largely to the intake of fat-soluble vitamins and help achieve the recommended intakes for vitamins A, D and E for some part, but not all of the population [8
]. However, while fortified foods are well adopted in the USA, Europeans are more skeptical of fortification [10
]. In Europe, non-fortified foods are the main source for most vitamins. Despite a uniform regularization within the EU, fortification and supplementation practices differ substantially between countries [1
It has been repeatedly reported in European studies that voluntarily-fortified foods can have a significant impact on reducing the proportion of inadequate intakes within a population [1
]. Supplements generally have a more important contribution to total vitamin intake than voluntarily-fortified foods, but are often less effective at reducing the proportion of suboptimal intakes due to insufficient adherence [3
]. In response to very low intakes (e.g., vitamin D), national encouraged fortification can play an important role in the reduction of inadequacies. In Finland, vitamin D fortification of dairy products and fats was successfully introduced as a strategy to improve vitamin D status in the entire population [13
Despite the positive effects of fortified foods and supplements, excessive intake of fat-soluble vitamins can lead to adverse health effects [14
]. In general, however, only a small proportion of the population, mainly children, exceeds the upper intake level (UL) [1
]. A general concern of excessive intakes remains when for certain nutrients, both fortification and supplementation practices are common [1
]. Vitamins with a relative low UL in comparison to the recommended intakes, like vitamins A, D and E, need special attention [3
In Belgium, fortified foods and supplements require notification, and the level of vitamins added is governed by the Belgian Royal Decree (Koninklijk besluit (KB) 3/3/1992). Fortification in Belgium is mandatory for margarines (fat content (FC) > 80%) and spreadable fats (39% < FC < 41%) (KB 02/10/1980) and officially encouraged for spreadable fats with other fat contents. Nutritive fortification values of margarines and spreadable fats however are currently based on nutritive values of butter (Table 1
Similar to other countries, the Belgian Superior Health Council advises a vitamin D supplement for the entire population in the case of minimal exposure to sunlight [15
]. Independently of their intake from food, a supplementation of 10 μg/day for children and 15 μg/day for adolescents and adults is recommended. This supplementation advice however is currently based on the population reference intake. Dietary intake data are needed to fine-tune these recommendations in correspondence with Belgian dietary habits, as well as with intake from fortified foods and supplements [17
When designing strategies to combat inadequate or excessive intakes, it is important to evaluate the efficacy of the actual fortification and supplementation programs. Knowledge of the intake distribution of fat-soluble vitamins and the contribution of all sources is therefore required [1
]. In Belgium, those studies are scarce. One study evaluated the intake of micronutrients in Flemish preschool children (2.5–6.5 years). Unfortunately analyses of fat-soluble vitamins were confined to vitamin D, and dietary supplements were hereby not taken into account [18
]. Nevertheless, in the review study of Mensink et al., raw data from eight countries were uniformly re-analyzed to evaluate inadequacies of micronutrients in Europe. This study included results for vitamin A, D and E from the Flemish children study [4
The current study aims to evaluate the contribution of mandatorily fortified foods, voluntarily fortified foods and supplements to the intake of fat-soluble vitamins in the general Belgian population (3–64 years) and to compare usual intake to dietary reference values. As food consumption varies by age and gender, the intake distributions were stratified by age and gender.
To our knowledge, the current study is the first evaluation of the risk of inadequate and excessive intakes of vitamins A, D, E and K in the general Belgian population taking account all sources, i.e., foods, fortified foods and supplements. Additionally, this study differentiates between mandatorily and voluntarily fortified foods as such, providing better insights in the current Belgian fortification and supplementation practices.
Our study revealed considerable inadequate intakes for vitamin A, from all sources, in the entire Belgian population. Median vitamin D intake from all sources was less than one third of the AI in all subgroups. The lowest intake values for vitamin A and D were found in adolescents. The risk for inadequate intake from vitamin E and K was low.
In Belgium, mandatory fortification of margarines and spreadable fats slightly decreased vitamin A inadequacies, but did not improve suboptimal intakes of vitamin D. Voluntarily fortified foods and supplements made a substantial contribution to the usual intake of vitamins D and E. Nonetheless, the effect on inadequacy risk for vitamin D was minor while inadequacies of vitamin E were substantially reduced. A small proportion of young children were at risk of exceeding the upper intake level of vitamin A, which was mainly related to higher intakes from the base diet. A minor proportion of adult woman and young children exceeded the UL for vitamin D when including supplements.
5.1. Intake and Inadequacies
Except for vitamin D, which is mainly produced under the influence of UVB-radiation, a well-balanced and healthy diet should provide the required amount of vitamins [2
]. Inadequate vitamin A intake in the Belgium population could consequently be related to the unbalanced consumption of vegetables and dairy products, which are important food sources for vitamin A [35
]. The consumption of vegetables and dairy products in 2014 was far below the reference values for the entire Belgian population, in particular in adolescents [41
Because of the magnitude of the difference between median intake and the AI, we presume inadequate intake of vitamin D in all sex-age groups of the Belgian population. It should be kept in mind that these findings are valid under minimal sun exposure. Although, since Belgian life style is characterized by longer working days indoors and less outdoor activities, limited vitamin D body reserves from sun exposure might be more frequently occurring in Belgium than expected. Especially in winter-time when we rely on those body reserves, this might lead to inadequate status of vitamin D [5
]. To our knowledge, no representative country data are available on vitamin D status in Belgium. The available studies are restricted to subgroups of the population and not always related to seasonal variability. However, an indication of the prevalence of low vitamin D status in Belgium is given by the studies of Sioen et al., Hoge et al. and Mac Farlane et al. that described high prevalence of vitamin D deficiency (25(OH)D <50 nmol/l) among Belgian children and adults [42
Comparing dietary intake data with other European studies is hampered by the heterogeneity in assessment methods and by the difference in age classifications and in dietary reference values used to evaluate adequacy. Nevertheless, the present results are in line with European review studies when comparing intake levels. Higher intakes of vitamin A from foods are found in countries (Germany, Poland, Italy) with high consumption of sausages, liver and vegetables [3
]. Higher vitamin D intake levels from food are found in Scandinavian countries were oil-rich fish and milk are more frequently consumed [4
]. Our results for vitamin D intake from foods and fortified foods in young children (3–6 years) were somewhat higher, but in the same order as the results of the Flemish preschoolers [18
Comparable to our study, notable discrepancies between mean intake and dietary recommendations for vitamins A and D are common in different European populations and in all sex-age groups. However, the proportion of inadequate vitamin A intakes in the Flemish preschoolers (4–10) were almost twice as high as in our study [18
]. This can be explained by the higher reference values used in the latter study.
In contradiction to our results, Mensink et al. reported substantial proportions of inadequacies for vitamin E in all sex-age groups. However, intake data of fortified foods were generally lacking in this study [4
]. Vitamin K intake data should be evaluated with caution due to uncertainties and limitation of food composition tables. Belgian intake data for vitamin K fell within the ranges reported in other European studies [36
5.2. Fortified Foods and Supplements
The market of fortified foods and supplements in Europe is known to be a challenging market environment [10
]. Despite a uniform European regulation on the addition of vitamins and minerals to foods (1925/2006), additional national legislations are adopted defining limited amounts of the added nutrients or national policies are set on mandatory fortification. As a result, fortification practices and consumption of fortified foods differ greatly between European countries [1
]. In Belgium, children and adolescents generally consume more fortified foods than adults [40
]. This reflects the substantial amount of foods designed for children and adolescents found in our inventory. The age-related decline of fortified food consumption is also substantiated by different European studies [1
Although studies including the intake from fortified foods are limited, the available evidence indicates that voluntarily fortified foods can make a substantial contribution to dietary intakes and can reduce the risk of sub-optimal intakes at the population level of a range of micronutrients, among which are vitamins D and E [1
]. Our results for vitamin E are in line with German results reporting fortified foods to be effective in raising low intake values of vitamin E closer to the reference values [1
]. For vitamin D, however, we did not observe the same effect. Indeed, inclusion of fortified foods barely increased median vitamin D levels in the Belgian population.
In Europe, large differences exist in supplement consumption. Important contributions of supplements to total intake were frequently reported for vitamin D. Nevertheless, due to low uptake, supplements are often not effective as a public health strategy [12
]. Our results are in line with these findings.
5.3. Excessive Intakes
In Europe, the risk for excessive intake of micronutrients taking into account all sources is low. Excessive intakes are mainly found in children, but the UL is exceeded by only a small proportion of children [1
]. Concerning fat-soluble vitamins, excessive intakes were reported for retinol. Excessive intakes for retinol were mainly related to higher intakes from the base diet (Poland) or from supplements (Ireland). Fortified foods had little effect on the higher intakes (P95) due to the limited amounts of foods fortified with retinol. These results are in line with our findings.
The review studies of Hennessey and Flynn concluded that the risk of adverse health effects in individuals exceeding the UL was minor due to the safety margins used in establishing the UL and given the fact that the UL is exceeded by a modest amount [1
]. In our study, the risk for high exposure of retinol is also limited in time, as it was only observed among the youngest age group.
In Europe, the risk for exceeding the UL of vitamin D is low, even in countries with a wide use of supplements [3
]. In our study, high supplement intakes were generated from highly-dosed substances. In Belgium, vitamins with daily doses higher than 50 μg/day are considered as drugs. These drugs however are available at the pharmacist without prescription and therefore also taken into account in the usual intake estimations.
5.4. Strengths and Limitations
The importance of the evaluation of fortification and supplementation practices has been repeatedly stressed in previous works. The need to adapt survey methodologies to include intake data from all sources was hereby highlighted. Studies evaluating intake from all sources in Europe are scarce. These studies have been hampered by the complex research task required. Food and supplement composition tables need to be in line with the supply and nutritive values of fortified products on the market today [1
]. To facilitate this, automatic adaptation of food composition tables with labelled values of fortified nutrient contents through bar-codes (e.g., Global standard one (GS1)) would encompass a serious reduction of the comprehensive task required.
An important strength of this study is that the contribution of fortified foods and supplements to total vitamin intake was evaluated. The survey methodology comprised a market inventory to assure that computation of vitamin intake was based on the most recent nutritive values. Furthermore, data were collected through the combination of two 24-h recalls and a supplementary FFQ, which is recommended by EFSA as a dietary assessment method [20
]. Finally, vitamin intake was modelled with SPADE, a statistical program coping with multimodal distributions and heterogeneous variances between sources, typical for intake estimations from different sources [15
This study however was confined to subjects aged 3–64 years. Besides the fortified foods presented in Table 1
, our market investigation revealed a considerable amount of foods designed for infants and toddlers, like infant milk, follow-up milk, growing-up milk, milk cereals and dairy desserts for babies. The contribution of fortified foods and supplements might consequently differ greatly in these youngest age groups. This will have an impact on the risk of inadequate and excessive intake in those population subgroups and consequently on the national recommendations to be made in nutrition policy. It would therefore be advisable to additionally conduct ad hoc surveys in specific target populations like infants and toddlers.
A limitation of the study is that no biological samples were collected. For vitamin D, for which cutaneous synthesis excited by sun exposure is the main source, serum 25(OH)D levels would be required to give a picture on vitamin D status in the Belgian population and stress the magnitude of the evaluated vitamin D deficiency.
Another limitation of the study was that subjects with missing data of FFQ on supplements were all treated as non-users when they did not consume supplements on both the 24-h recalls. This conservative approach implies a possible underestimation of the intakes from supplements.
At last, the study did not include frequency questions on the consumption of dietary supplements. As a consequence, the intake values of subjects taking higher doses of supplements on a weekly or monthly basis had to be treated as users with missing data on the 24-h recall to enable modelling. This implies also a bias in the estimation of supplement intakes.
It is clear that fortification and supplementation practices in Belgium are insufficient to overcome inadequacies of vitamins A and D in the Belgium population. There is a need for dietary strategies to increase vitamin A and D intakes in the entire Belgian population. Intake data of the Belgian population provide an ideal starting point for modelling of fortification and supplementation scenarios. These scenario analyses will be very useful from a policy point of view. They should allow identifying which measures will ensure effective and safe increases in vitamin A and D intake. Fortification of margarines and fats in Belgium with vitamins A and D is currently based on nutritive values of butter. These scenario studies might give an insight into how a potential change in policy may affect intake levels of vitamins A and D at a population level [15
]. However, it should be stressed that there is a need for nationally-representative data on vitamin D status in the Belgian population prior to setting out the final recommendations on vitamin D intake.