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College of Pharmacy and Nutrition, University of Saskatchewan, Saskatoon, Saskatchewan, Canada S7N 5C9 and * Office of Applied Research and Safety Assessment, Center for Food Safety and Applied Nutrition, U.S. Food and Drug Administration, Laurel, MD 20708
2 To whom correspondence should be addressed. E-mail: susan.whiting{at}usask.ca.
The symposium "Optimizing Vitamin D Intake for Populations with Special Needs: Barriers to Effective Food Fortification and Supplementation," presented at the Experimental Biology meeting in 2005, examined the reasons why, with so much evidence indicating a greater need for dietary intake of vitamin D (1–4), there remain many barriers to providing enough vitamin D in foods to meet newly emerging, higher recommendations (1,3–6). One reason for concern about vitamin D nutrition is its relatively low tolerable upper intake level (UL) (7); therefore, we wanted to examine the reasons for the current UL as well as determine what higher value would be safe (8). Further, most of the recent attention concerning vitamin D nutrition has concentrated on young and middle-aged Caucasian adults whose vitamin D requirements would be less than those of other population groups. Therefore, this symposium focused on the needs of youth in areas with no winter cutaneous synthesis of vitamin D and on older adults, and also examined the special concerns for those with darkly pigmented skin that impedes cutaneous vitamin D synthesis. In addition, we wished to view the situation in the US and Canada, where there is some degree of vitamin D fortification (9), and to contrast it with countries where vitamin D fortification has only recently been implemented. Finally, we wanted to begin to address strategies for improving vitamin D intake.
In 2004, the Experimental Biology symposium entitled "Vitamin D Insufficiency: A Significant Risk Factor in Chronic Diseases and Potential Disease-Specific Biomarkers of Vitamin D Sufficiency" raised issues related to vitamin D requirements (1,2,4,10–12). Several speakers specifically addressed the need to increase vitamin D intake to meet a new standard of adequacy (1,2,4). Two speakers addressed how vitamin D was involved in diseases not related to calcium metabolism (10,11), highlighting the need for further research into requirements based on all the biological actions of vitamin D (4,6). The 2004 symposium could not address many issues related to special needs and barriers to meeting these needs. Hence, a second symposium, in 2005, addressed special needs and provided ways to identify and overcome barriers for adequate vitamin D nutriture; the papers from this symposium are published in this issue of the Journal of Nutrition.
An important consensus in the area of vitamin D research is that the measure of vitamin D adequacy has shifted from one representing absence of deficiency to one representing absence of insufficiency (3–6). Circulating 25-hydroxyvitamin D [25(OH)D], the transport and storage form of vitamin D, is the major indicator of status. It originates from cutaneous synthesis upon exposure to appropriate UVB radiation, but it is also influenced by vitamin D intake. As illustrated in Figure 1, when the dietary reference intakes were set in 1997 (7), a cutoff of 30 nmol/L of 25(OH)D was chosen as the criterion of adequacy. In 2005, the cutoff for adequacy is 
80 nmol/L (1–6).
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A second group with special needs includes persons with darkly pigmented skin, whose cutaneous vitamin D synthesis is very low, especially when living at higher latitudes. In the US, African Americans are at risk for vitamin D insufficiency despite having much greater skeletal mass than the non-African American population. Dr. Susan Harris (14) outlines the reasons why this group deserves special consideration. For example, the circulating levels of 25(OH)D and dietary intake of vitamin D are low, and the risk for chronic diseases related to immunity, such as diabetes and certain cancers, is greater. Together, these factors suggest that action is needed to improve vitamin D status and consideration should be given to the specific food vehicles that are fortified with vitamin D as an important strategy for improving vitamin D status in this population. Information concerning the consumption of the two chief fortified food sources in the US shows similar patterns of intake over the last two decades (15), with African Americans consuming significantly less vitamin D from milk and milk products and from ready-to-eat breakfast cereals (Table 1).
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Barriers to providing vitamin D. Symposium speakers identified barriers to achieving adequate vitamin D status. Whereas vitamin D status is determined from both sun exposure and dietary intake, the discussion was limited to improving status through dietary intake. In particular, fortification and supplementation are considered (16,17) because natural food sources rich in vitamin D, such as oily fish, are relatively uncommon in most countries (12).
Before effective strategies to raise population intake of vitamin D can be implemented, concern regarding vitamin D toxicity must be addressed. Although adverse effects of vitamin D can lead to disability and death, these occur only at very high intake. The UL for vitamin D should represent the lowest safe level of intake that has been established using published evidence. The current UL has been criticized for being too conservative, thus impeding research into requirement levels that may be above the current UL. Dr. Reinhold Vieth (8) describes how the current UL was set and provides evidence for an upward change. He indicates that the value for which there has been no observed adverse effect (i.e., the NOAEL) is 265 µg, in contrast to the current UL, which is 60 µg (Fig. 1). The UL has taken on implications beyond its originally intended purpose of dietary planning, but possibly none is as important or as far-reaching as its regulatory application in establishing safe limits to the amount of vitamin D that can be added to foods or the maximal amount that can be contained in over-the-counter dietary supplements or meal replacement products (18).
In Figure 1, we provide an overall summary of the three critical shifts to the right that have taken place in considering vitamin D: a shift to a higher value of circulating 25(OH)D for measuring status; a shift to a higher value for setting the nutrient recommendation; and a shift upward to the highest intake level that causes no adverse effects, which also implies a shift upward in the UL. To accommodate increased need for dietary sources of vitamin D, one can consider promoting increased intake of natural sources of vitamin D, of foods fortified with vitamin D, and of supplements containing vitamin D. As shown in Figure 2, Americans are very reliant on fortified foods, which provide between 65%–87% of vitamin D intake. As intake itself is rather low (means for these age groups range from 3.7–6.0 µg/d), strategies are needed to improve intake. Fortification is currently being promoted as a viable strategy (19).
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FOOTNOTES |
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LITERATURE CITED |
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 TOP LITERATURE CITED |
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1. Hollis BW. Circulating 25-hydroxyvitamin D levels indicative of vitamin D sufficiency: Implications for establishing new effective dietary intake recommendations for vitamin D. J Nutr. 2005;135:317–22.
2. Hanley D, Davison KS. Vitamin D "insufficiency" in North America. J Nutr. 2005;135:332–7.
3. Dawson-Hughes B, Heaney RP, Holick MF, Lips P, Meunier PJ, Vieth R. Estimates of optimal vitamin D status. Osteoporos Int. 2005;16:713–6.[Medline]
4. Whiting SJ, Calvo MS. Dietary recommendations for vitamin D: a critical need for functional end points to establish an estimated average requirement. J Nutr. 2005;135:304–9.
5. Heaney RP. Long latency deficiency disease: insights from calcium and vitamin D. Am J Clin Nutr. 2003;78:912–19.
6. Holick MF. The vitamin D epidemic and its health consequences. J Nutr. 2005;135:2739–48.
7. Institute of Medicine. Dietary reference intakes for calcium, phosphorus, magnesium, vitamin D and fluoride. Washington, DC: National Academy Press; 1997. p. 250–87.
8. Vieth R. Critique of the considerations for establishing the tolerable upper intake level for vitamin D: critical need for change upwards. J Nutr. 2006;136:1117–22.
9. Calvo MS, Whiting SJ, Barton CN. Vitamin D fortification in the US and Canada: current status and data needs. Am J Clin Nutr. 2004;80:1710S–6S.
10. Harris S. Vitamin D in type 1 diabetes prevention. J Nutr. 2005;135:323–5.
11. Gross MD. Vitamin D and calcium in the prevention of prostate and colon cancer: new approaches for the identification of needs. J Nutr. 2005;135:326–31.
12. Calvo MS, Whiting SJ, Barton CN. Vitamin D intake: a global perspective of current status. J Nutr. 2005;135:310–6.
13. Heaney RP. Barriers to optimizing vitamin D3 intake for the elderly. J Nutr. 2006;136:1123–5.
14. Harris S. Vitamin D and African Americans. J Nutr. 2006;136:1126–9.
15. Moore CE, Murphy MM, Holick MF. Vitamin D intakes by children and adults in the United States differ among ethnic groups. J Nutr. 2005;135:2478–85.
16. Tylavsky FA, Cheng S, Lyytikäinen A, Viljakainen H, Lamberg-Allardt C. Strategies to improve vitamin D status in northern European children: exploring the merits of vitamin D fortification and supplementation. J Nutr. 2006;136:1130–4.
17. Calvo MS, Whiting SJ. Strategies to overcome barriers to optimal vitamin D status in populations with special needs. J Nutr. 2006;136:1135–9.
18. Institute of Medicine. Dietary reference intakes: guiding principles for nutrition labeling and fortification. Washington, DC: National Academy Press; 2004. p. 124–44
19. Newmark HL, Heaney RP, Lachance PA. Should calcium and vitamin D be added to the current enrichment program for cereal-grain products? Am J Clin Nutr. 2004;80:264–70.
20. Calvo MS, Barton CN pp.124–44 Racial differences in vitamin D intake, dietary supplement use and vitamin D status among black and white men and women in the NHANES III Survey. Proceedings of the Vitamin D Workshop Meeting on Vitamin D and Cancer, NIH, Bethesda, MD, 17–19 November, 2004 (abstract).
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  M. S. Calvo and S. J. Whiting Public Health Strategies to Overcome Barriers to Optimal Vitamin D Status in Populations with Special Needs J. Nutr., April 1, 2006; 136(4): 1135 - 1139. [Abstract] [Full Text] [PDF]
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