Expert Summary: Vitamin D Requirements
Professor and Head, Division of Nutrition and Dietetics, College of Pharmacy & Nutrition, University of Saskatchewan
Although Canadians rely on diet and/or supplements to help maintain proper vitamin D status, our intake of vitamin D does not meet current recommendations. Theoretically, vitamin D needs could be met by skin synthesis. However, environmental factors during winter and sunscreen use in summer prevent Canadians from attaining adequate UVB exposure.
Although there still exists some debate about what constitutes adequate vitamin D status, a circulating level of 75 nmol/L of 25-hydroxyvitamin D [25(OH)D] is currently accepted as the cutoff for vitamin D sufficiency.1 At this level, calcium absorption is maximal, PTH is suppressed, muscle strength is improved and risk of falls is minimized, and there is a lower risk of osteoporotic fractures.2,3 Evidence from nonskeletal conditions, such as cancer and immune diseases, suggests risk reduction occurs at 25(OH)D levels above 75 nmol/L.1,3
Current vitamin D dietary recommendations were made in 1997,4 when a new paradigm of dietary recommendations called Dietary Reference Intakes (DRIs) was initiated. DRIs for vitamin D were set to maintain 25(OH)D at 30 nmol/L, thereby preventing rickets and osteomalacia. Since that time, research has shown new roles for vitamin D beyond rickets and osteomalacia prevention.1-3 This has led to discrepancies between the recommendations made by Health Canada (the 1997 DRIs) and various health organizations (see graph).5,6,7
Average daily intake levels of vitamin D and recommended levels
Average = intake of Canadians ≥1 year of age;
Ideal = intake according to Canada’s Food Guide;
Ideal + Supplement of 400 IU (per Canada’s Food Guide) for persons over 50 years;
DRI for >70 years = recommendation by Institute of Medicine in 1997;
OC = Osteoporosis Canada guidelines (2002) for persons >50 years;
CCS = Canadian Cancer Society recommendation (2007) for adults;
CPS = Canadian Pediatric Society;
UL = upper level set as highest intake considered safe (1997). 1 µg = 40 IU.
Canadians’ average intake of vitamin D is 5.8 µg.8 The “ideal” intake recommended by Canada’s Food Guide (CFG) - two servings/day milk, two servings/week fatty fish and moderate use of margarine -provides only 7.6 µg. Adding a 400 IU supplement is recommended for individuals over 50 years9 and would bring the ideal intake level to 17.6 µg, but only a fraction of our population takes them.10
None of these “new” recommendations (shown in the graph) exceed the current upper level (UL) for vitamin D of 50 µg (2000 IU) for individuals over one year of age. By definition, the UL is actually a safe intake with negligible risk for adverse effects.4 In fact, vitamin D may be ingested to levels of 250 µg (10,000 IU) by adults with no evidence of harm.11 However, until DRI values are revised, it is prudent to advise that intake not exceed 50 µg (2000 IU) without monitoring by a health professional.
Highlights
- The average Canadian diet does not provide enough vitamin D to achieve risk reduction for skeletal and nonskeletal diseases.
- Vitamin D fortification of foods is necessary as are strategies to promote the regular use of supplements in adults over 50 years.
- Optimum foods for fortification include cheese and yogourt since they are known sources of calcium and are often presumed also to contain vitamin D.
References
- Holick MF. 2007. Vitamin D deficiency. N Engl J Med 357:266-281.
- Bischoff-Ferrari H et al. 2006. Estimation of optimal serum concentrations of 25-hydroxyvitamin D for multiple health outcomes. Am J Clin Nutr 84:18-28.
- Heaney, RP. 2007. The case for improving vitamin D status. J Steroid Biochem Mol Biol 103:635-641.
- Institute of Medicine. 1997. Dietary Reference Intakes for calcium phosphorus, magnesium, vitamin D and fluoride. National Academy Press, Washington DC.
- Brown JP, Josse RG. 2002. Clinical practice guidelines for the diagnosis and management of osteoporosis in Canada. CMAJ 167(10 Suppl):S1-34.
- Canadian Cancer Society. http://www.cancer.ca/ccs/internet/standard/0,3182,3172_1176359459_langId-en,00.html. Accessed 10/10/2007.
- Canadian Pediatric Society. 2007. Vitamin D supplementation: recommendations for Canadian mothers and infants. Paediatr Child Health 12:583-589.
- Vatanparast H, Whiting, SJ (unpublished). Data from Canadian Community Health Survey (CCHS) Cycle 2.2, 2004.
- Health Canada. 2007. Vitamin D for people over 50: Background. http://www.hc-sc.gc.ca/fn-an/food-guide-aliment/context/evid-fond/vita_d_e.html. Accessed 10/10/2007.
- Troppmann L et al. 2002. Natural health product use in Canada. Can J Publ Hlth 93:426-430.
- Hathcock JN et al. 2007. Risk assessment for vitamin D. Am J Clin Nutr 85:6-18.
Keywords: vitamin D
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