© 2006 American Society for Nutrition
J. Nutr. 136:1130-1134, April 2006
Symposium: Optimizing Vitamin D Intake for Populations with Special Needs: Barriers to Effective Food Fortification and Supplementation
Strategies to Improve Vitamin D Status in Northern European Children: Exploring the Merits of Vitamin D Fortification and Supplementation1
Frances A. Tylavsky*,2,
Sulin Cheng
,
Arja Lyytikäinen,
Heli Viljakainen** and
Christel Lamberg-Allardt**
* Department of Preventive Medicine, University of Tennessee Health Science Center, Memphis, TN; Department of Health Sciences, University of Jyväskylä, Jyväskylä, Finland; and ** University of Helsinki, Helsinki, Finland
2 To whom correspondence should be addressed. E-mail: ftylavsky{at}utmem.edu.
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ABSTRACT
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Adequacy of vitamin D in children in Europe has been the focus of a number of investigations. The results of measuring serum levels of 25-hydroxyvitamin D show high prevalence of vitamin D deficiency during the winter with lower prevalence during the summer. National policies on food fortification or individual supplementation with vitamin D have been recently revisited by the individual countries and the European Union as a whole. Optiford is a project managed by a coalition of scientists formed to optimize vitamin D fortification in the northern European Countries, was given the task to decide if food fortification with vitamin D is feasible and to provide a scientific basis for setting the vitamin D fortification level in Europe. This article presents the results of these investigations to date, with particular attention to potential corrective strategies to allow children and adolescents living in countries at high latitudes to maintain healthy circulating 25-hydroxyvitamin D levels year around, even in the absence of adequate sun exposure during a significant part of the year.
KEY WORDS: • vitamin D • adolescents • nutrition • dietary supplementation • food fortification • serum 25(OH)D
Overview of Optiford.
Optiford, a coalition of scientists representing various countries in Europe, was convened and funded by the European Union Commission in 2000. Funding was provided for 4 y to decide if food fortification with vitamin D is feasible and to determine the level for fortification in an effort to provide a scientific basis for vitamin D supplementation policies in Europe. The group identified 5 specific aims for the focus of their efforts with particular concentration on high-risk populations (Table 1). Work packages were funded by the European Commission to conduct targeted research. This article will report on the Optiford experience to date. In order to compare food-fortification approaches to the individual use of dietary supplements, we also provide a review of pertinent studies conducted in northern Europe that have examined the efficacy of vitamin D-containing, dietary-supplement use in children and adolescents.
Initial assessment of vitamin D status in children across European countries.
An accurate, unconfounded assessment of the current vitamin D status in children residing in the Optiford countries was needed before any decisions concerning levels of fortification or need of dietary supplementation could be evaluated. There have been several reports detailing the prevalence and risk factors for vitamin D deficiency across European countries (1–8); however, there are difficulties in comparing the outcomes of these studies due to differences in study design, variability in assays measuring circulating levels of 25-hydroxyvitamin D [25(OH)D]3 (9), geographic latitude of the population under study, and the age range, ethnicity, and gender of the samples. The Optiford group designed a study to recruit a random sample of adolescent girls and elderly women in 4 countries: Ireland, Finland, Poland, and Denmark (Fig. 1). The sample included 199 girls and 221 older women, all living between 51 and 60 degrees N latitude. At these latitudes, UV light capable of producing vitamin D from sun exposure is absent from September through March (10). Serum 25(OH)D levels from all participants were measured between February and March of 2002. The participants were randomly selected from national registries in Denmark and Poland. In Finland, the older women were randomly selected from the national registry and the girls were recruited from schools via letters to parents. In Ireland, the sample was a convenience sample from volunteer organizations and schools. Overall, the sample represents girls who would be considered to have normal weight. The prevalence of serum 25(OH)D deficiency measured <10 ng/L (<25 nmol/L) and suboptimal serum 25(OH)D levels were in the range of 10–19 ng /L (25–47.5 nmol/L) (Fig. 2). The prevalence of serum 25(OH)D deficiency in the adolescent population ranged from 26 to 51% (Fig. 2). At the cutoff point for suboptimal levels, i.e., <19 ng/L (<47.5 nmol/L), >90% of the adolescents were suboptimal in vitamin D, while <50% of the elderly had suboptimal 25(OH)D levels. This suggests that either the adolescents are at a higher risk of deficiency or their dietary habits and exposure to the sun are different from that of the elderly women.
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FIGURE 1 Circles identify the countries providing samples of young (y) and old females (o) for baseline assessment of serum 25(OH)D status for Optiford's fifth aim: to determine the contribution of sun exposure and diet to serum 25(OH)D during a 1-y period. The numbers indicate the sample size for each age group per circled country.
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FIGURE 2 Percent of young (12.5 ± 0.5 y, n = 199); and old (71.8 ± 1.4y, n = 221) with serum 25(OH)D considered to be deficient (<25 mmol/L) or suboptimal (25–47.5 mmol/L) graphed from data presented in Andersen et al. (11).
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Vitamin D and calcium intake from diet was assessed using a standardized food frequency questionnaire with a common food composition database (11). In all cases, the adolescents had lower vitamin D intake than the elderly, but not sufficient enough to account for the great disparity in the prevalence of suboptimal or deficient circulating levels of 25(OH)D observed between the adolescents and the elderly (Fig. 3). A second measurement of serum 25(OH)D was taken in June through August of 2002, and a third was drawn in the winter of 2003 from all participants in the study. Preliminary findings confirm those from an earlier research report (6) that the prevalence of suboptimal serum 25(OH)D levels is below 5% in summer due to adequate sun exposure (data not shown). In addition, at the end of winter in 2003, serum 25(OH)D levels were similar to baseline.
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FIGURE 3 Mean dietary intake of vitamin D and calcium, for young (12.5 ± 0.5 y, n = 199); and old (71.8 ± 1.4y, n = 221) females from each country graphed from data presented in Andersen et al. (11). Nordic countries recommended levels: calcium, 900 mg/d; vitamin D, 5 µg/d.
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History of vitamin D food fortification and dietary supplementation policy in Finland.
Vitamin D food fortification and dietary supplementation policies in Finland are regulated by separate government agencies. Approval for the addition of vitamin D to food must be obtained by the National Food Agency (Ministry for Trade and Industry); recommendations for vitamin D supplement use by adults and children are issued by the Ministry for Health and Social Affairs. Vitamin D is considered to be a pharmacologic agent for children when the dose is higher than the Nordic countries' recommended levels of 5 µg/d (200 IU/d) (12). Individuals are required to secure a prescription from a physician in order to obtain a vitamin D preparation that contains >5µg.
The vitamin D policy in Finland prior to 2002 recommended that exclusively breast-fed infants receive 10 µg (400 IU) of vitamin D3. The level of supplementation of D3 for other infants and children up to age 3 varied and depended on the use of breast-milk substitutes and the use of vitamin D fortification of children's foods, such as cooked cereals. Although there were recommendations that older children and the elderly should receive extra vitamin D, there was no formal policy in place. Thus, parents of infants and children up to age 3 were able to obtain vitamin D supplements from the Health Service without a specific prescription from a physician. Consequently, there was no program in place that provided vitamin D3 supplements to older children or adolescents. However, in 2002, the margarine in Finland was fortified at the level of 7.5 µg/100 g or the equivalent of 0.4 µg of vitamin D3 for each teaspoon of margarine. This is lower than the maximal 8.27 µg/100 g of vitamin D2 or D3 allowed in the U.S. or the 13.2 µg/100 g required in all Canadian margarine (13).
Screening data from a study of pre- and early-pubertal children showed low vitamin D intake in children of <2.9 µg/d (110 IU/d) (14). This report, in combination with numerous reports of high prevalence of 25(OH)D deficiency during wintertime (2) and the link between suboptimal 25(OH)D and lower bone density (1,4,15), stimulated the reassessment of the vitamin D policy in Finland. An expert meeting was convened in 2002 to discuss vitamin D status in the Finnish population. The evidence for suboptimal vitamin D intake and serum levels of 25(OH)D was reviewed. Calculations were made on how different fortification approaches would affect vitamin D intake in the population. The estimated projected increase in vitamin D intake by fortifying milk, margarine, spreads, or breads was presented to the expert committee (Table 2; Fig. 4). The committee decided to fortify milk and margarine at the level of 5 µg /100 g for milk, sour milk, and yogurt, and at 10 µg/100 g for margarine or spreads. Projected increases in vitamin D intake were then calculated for specific age and gender groups based on these levels of vitamin D fortification of 2 commonly consumed food staples. Three-day food records from 322 adolescents (14–16 y) participating in ongoing research studies were used to make these calculations. The mean, median, 10th, and 90th percentile of vitamin D intake provided by the diet under the pre-2002 fortification policy and how vitamin D fortification of milk and margarine or spreads affect the vitamin D intake of adolescents is shown in Table 2. With this modest level of fortification, it was estimated that >50% of the adolescent population would meet or exceed the Nordic countries' reference dietary intake for vitamin D from diet alone.
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FIGURE 4 Frequency of reported vitamin D intake (µg/d) based on food records of 200 12–17 y olds who have participated in research studies in various locations in Finland.
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The histogram in Figure 4 shows the frequency of the levels of total dietary vitamin D intake under the pre-2002 policy and the frequency distribution if bread were fortified with 2 µg/100 g (80 IU/100 g) of vitamin D3. As would be expected, the fortification of wheat and rye bread would shift the frequency of vitamin D consumption to the right. Based on these calculations, the majority of adolescents would consume between 4 and 9 µg/d (160–360 IU/d) of vitamin D each day.
At the conclusion of the conference, the recommendation was made to fortify milk, sour milk, and yogurt with 0.5 µg/100 g (20 IU/100 g) and increase the fortification of margarine and spreads for individual consumption from 7.5 µg to 10 µg/100 g (400 IU/100 g). At these levels of fortification, a cup of milk would contain 1 µg of vitamin D3 (40 IU) compared with 2.5 µg per cup (100 IU) that is currently available in the US/Canadian market. One teaspoon of margarine would yield 0.5 µg in Finland (16). The regulations governing the fortification of milk, yogurt, margarine, and spreads with vitamin D3 were initiated in Finland in February of 2003. Although the Finnish vitamin D fortification policy was not made mandatory, as in other countries, most companies complied with the option to fortify.
Efficacy assessment of vitamin D food fortification policy in Finland.
To evaluate the impact of the new vitamin D fortification policy in Finland, children and adults were recruited from 6 cities in Finland (Rovaniemi, Kuopio, Tampere, Turku, Jyväskylä, and Helsinki). Individuals were recruited based on participation in various research studies already established. Some of the participants were randomly recruited (Rovaniemi, Kupio, Tampere, and Turku) and others represented convenience samples (Jyväskylä and Helsinki). Blood samples and dietary data (3-d food records or food frequency questionnaires) were collected from all subjects in mid-to-late winter in 2002 and 2004. The sample contains even numbers of males and females in all age groups. The actual increase in vitamin D consumption exceeded the projected increase in vitamin D intake for 12–14 y olds but fell short for the 15–17 y olds (Table 3). The pertinent question that needs to be addressed is whether these increases in vitamin D intake are enough to maintain serum levels during the long winter when UV rays are insufficient to produce adequate circulating 25(OH)D.
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TABLE 3 Projected and actual increase of vitamin D intake before and after fortification of milk, milk products, margarine, and other spreads in Finland
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Evaluation of the potential efficacy of dietary vitamin D supplement use.
The results of the vitamin D fortification study are not yet available; thus, we are unable to evaluate the merits of food fortification relative to the systematic use of vitamin D-containing dietary supplements in this article. However, we can make some general comparisons using 3 published studies (2,3,14) that provide information with which to estimate the effect of vitamin D supplementation on serum 25(OH)D in adolescents of these northern European countries. In the first study, pre- and peripubertal girls residing in Jyväskylä, Finland were randomized to receive 5 µg/d (200 IU/d) of vitamin D3 plus 1000 mg of calcium as a dietary supplement for 2 years. Serum 25(OH)D levels were higher at 12 mo and 24 mo (Fig. 5) (17). The blood samples were obtained in mid winter: therefore, these girls had been exposed to insufficient sunlight for at least 4 months and experienced little or no cutaneous synthesis of vitamin D (10). In another Finnish dietary supplement intervention study conducted by Lehtonen et al. (2), adolescent girls residing in Finland were measured in the wintertime to determine baseline serum 25(OH)D. Six months later (end of summer), their serum 25(OH)D levels increased due to sun exposure. Those individuals in the lowest tertile of serum 25(OH)D had the greatest gain in their serum values compared with those in the highest tertile of serum 25(OH)D. The prevalence of suboptimal serum 25(OH)D levels (<20 mmol/L) decreased from 14 to 0% due to sun exposure and from 75 to 2% for those considered to have suboptimal serum 25(OH)D levels (>20 mmol/L and <37.5 mmol/L). Serum 25(OH)D were not different from baseline in girls who received dietary supplements of 10 µg (400 IU) of vitamin D2 daily from October to February for 2 years. During the third year, a subgroup of girls were given 20 µg (800 IU) of D2 daily from October to February, which increased serum circulating concentrations of 25(OH)D slightly higher than baseline, but did not reach the levels that were attained during summer sun exposure.
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FIGURE 5 Serum 25(OH)D levels of Caucasian females randomized to 5 µg of vitamin D3 + 1000 mg of calcium (n = 46) at baseline, 12 mo, and 24 mo follow-up visits, modified from Cheng et al. (17).
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The third dietary supplement study was conducted at a lower, southern latitude in France. Guillement et al. (3) supplemented white adolescent boys during the winter months with 2.5 mg (10,000 IU) of vitamin D3 at the end of September, November, and January. Serum vitamin D levels were the same in September and March for those receiving the supplements, whereas for those who were not supplemented, serum 25(OH) levels fell by 40 nmol/L. Together, the results of these smaller studies suggest that serum 25(OH)D levels can be increased via dietary vitamin D supplementation, but the magnitude of this increase may vary depending on the amount of vitamin D synthesized over the summer months, the dosage used, the form of the supplement (D2 versus D3), and the length of time supplemented (winter vs. all year).
In summary, scientific evidences shows a high prevalence of wintertime deficiency and of suboptimal 25(OH)D levels in adolescents who live above the 51.9° N latitude. At these northern latitudes, a long day length and extended sun exposure during summer months reduces 25(OH)D deficiency to nearly zero. Modest fortification of milk and margarine does increase vitamin D intake in adolescents close to the Nordic countries' reference dietary intake; however, it is not clear if diet alone is sufficient to maintain adequate circulating 25(OH)D levels during the winter months. While dietary supplement use increases serum levels of 25(OH)D, the optimal dose, the optimal time required to supplement (winter months vs. whole year) and the most cost effective form of vitamin D to use (D2 or D3) remain to be determined. Clearly, there is still considerable research to be done before there can be a clear consensus as to which strategy is the most effective approach to maintain adequate circulating 25(OH)D.
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FOOTNOTES
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1 Presented as part of the symposium "Optimizing Vitamin D Intake for Populations with Special Needs: Barriers to Effective Mechanisms of Food Fortification and Supplementation" given at the 2005 Experimental Biology meeting on April 4, 2005, San Diego, CA. The symposium was sponsored by the American Society for Nutrition and supported, in part, by educational grants from the Centrum Foundation of Canada, the Coca-Cola Company, and the Natural Ovens Bakery, Inc. The proceedings are published as a supplement to The Journal of Nutrition. This supplement is the responsibility of the guest editors to whom the Editor of The Journal of Nutrition has delegated supervision of both technical conformity to the published regulations of The Journal of Nutrition and general oversight of the scientific merit of each article. The opinions expressed in this publication are those of the authors and are not attributable to the sponsors or the publishers, editor, or editorial board of The Journal of Nutrition, and do not necessarily reflect those of the Food and Drug Administration. The guest editors for this symposium publication are Susan J. Whiting, College of Pharmacy and Nutrition, University of Saskatchewan, SK, Canada and Mona S. Calvo, Center for Food Safety and Applied Nutrition, U.S. Food and Drug Administration, Laurel, MD, USA. 
3 Abbreviation used: 25(OH)D, 25-hydroxyvitamin D.
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LITERATURE CITED
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2. Lehtonen-Veromaa M, Mottonen T, Nuotio I, Irjala K, Viikari J. The effect of conventional vitamin D(2) supplementation on serum 25(OH)D concentration is weak among peripubertal Finnish girls: a 3-y prospective study. Eur J Clin Nutr. 2002;56:431–7.[Medline]
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11. Andersen R, Molgaard C, Skovgaard LT, Brot C, Cashman KD, Chabros E, Charzewska J, Flynn A, Jakobsen J, et al. Teenage girls and elderly women living in northern Europe have low winter vitamin D status. Eur J Clin Nutr. 2005;59:533–41.[Medline]
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13. Calvo, MS, Whiting, SJ, Barton, CN. Vitamin D fortification in the United States and Canada: current status and data needs. Am J Clin Nutr. 2004;80:1710S–16S.[Abstract/Free Full Text]
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15. Cheng S, Tylavsky F, Kroger H, Karkkainen M, Lyytikainen A, Koistinen A, Mahonen A, Alen M, Halleen J, et al. Association of low 25-hydroxyvitamin D concentrations with elevated parathyroid hormone concentrations and low cortical bone density in early pubertal and prepubertal Finnish girls. Am J Clin Nutr. 2003;78:485–92.[Abstract/Free Full Text]
16. Lamberg-Allardt C, Kärkkäinen M, Outila T, Natri A. Suomalaisten D-vitamiinitilanteen kohentaminen-auringosta, ruoasta vai purkista. [Improving vitamin D status in Finland – sun, food, or pills?] Suom Laakaril. Finnish Medical Journal 2003;58:1055–6.
17. Cheng S, Lyytikäinen A, Tylavsky F, Lamberg-Allardt C, Wang Q, Suuriniemi M, Alen M, Suominen H, Mahonen A, et al. Effects of calcium, dairy product, and vitamin D supplementation on bone mass accrual and body composition in 10-12-y-old girls: a 2-y randomized trial. Amer J of Clin Nutr. 2005:82;1147–8.
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