Vitamin D, as well as calcium, is essential to preventing osteoporosis and may reduce other health risks such as diabetes and immune system disorders. While exposure to sunlight provides vitamin D, Canadians are at risk of seasonal vitamin D deficiency because winter sunlight in northern latitudes above 35š does not contain enough ultraviolet B for vitamin D production. Supplementation is necessary to obtain adequate levels as dietary intake has minimal impact.
Current Canadian recommendations for "adequate intake" and "tolerable upper level" of vitamin D are more than 10 years old and were not based on properly conducted dose-finding studies.
The new guidelines recommend daily supplements of 400 to 1000 IU for adults under age 50 without osteoporosis or conditions affecting vitamin D absorption. For adults over 50, supplements of between 800 and 2000 IU are recommended. For people who need added supplementation to reach optimal vitamin D levels, doses up to the current "tolerable upper intake level" (2000 IU) are safely taken without medical supervision.
"A daily supplement of 25 mg (800 IU) should now be regarded as a minimum dose for adults with osteoporosis," writes Dr. David A. Hanley, University of Calgary Health Sciences Centre, Calgary, Alberta with coauthors. "Canadians can safely take daily vitamin D supplements up to the current definition of tolerable upper intake level (50 micrograms [2000 IU], but doses above that require medical supervision."
The authors conclude with a call for research into optimal doses and safe upper limits for vitamin D intake. "Despite a great deal of new research in the past decade, these major clinical questions have still not been addressed to the satisfaction of most experts in the vitamin D field."