Vitamin D: Sunshine and So Much More
(Page 5 of 6)
February/March 2008
By Linda B. White, M.D.
If you’re pregnant or nursing, you’ll also need more. Hollis and colleagues are currently researching the effects of different vitamin D doses in pregnant women of various races. Until the results of that trial are finalized, he can’t recommend more than 2,000 IU per day.
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When asked how much vitamin D they normally take, Hollis says he takes 4,000 IU a day, while Holick says each member of his family takes 1,000 IU of D3 a day. Holick also spends reasonable amounts of time outdoors.
Be aware that many supplements provide vitamin D as ergocalciferol (vitamin D2), rather than cholecalciferol (vitamin D3). D3 is the form naturally occurring in our bodies and is more effective.
No one really knows how much vitamin D might be too much; however, toxicity is exceedingly rare. The Food and Nutrition Board sets the upper level for daily dietary intake at 2,000 IU, though Hollis thinks that’s not enough to maintain health at northern latitudes. Accumulated research demonstrates 10,000 IU of vitamin D3 to be a more realistic upper limit.
Who’s at Risk?
The only way to measure vitamin D blood levels is to check a form of vitamin D called 25-hydroxyvitamin D. Doctors don’t routinely perform this test, and Holick thinks universal screening would be too expensive. If you’re at risk for, or already have symptoms of, deficiency, then you might want the blood test.
Just who’s at risk? Research shows the following populations face greater risk of vitamin D deficiency:
Dark-skinned people. Melanin darkens skin and absorbs UV light, which protects against sun damage and limits vitamin D production. Holick’s research shows that 80 percent of African-Americans studied in Boston over age 65 were vitamin D deficient — at the end of summer!
Northerners. People who live at higher latitudes where winters are long and dark run a higher risk of vitamin D deficiency. Holick notes that even fair-skinned people living above 37 degrees latitude make little vitamin D during the winter.
Older adults. The skin production of vitamin D and its activation in the kidneys declines with age. Further, the elderly typically spend more time indoors. Vitamin D deficiency in this age group contributes to osteoporosis and falls.
Breast-fed infants. Research in Iowa by Hollis and colleagues found that vitamin D deficiency, including severe deficiency, was common among breast-fed infants without vitamin D supplementation. Vitamin D deficiency in nursing mothers is the reason breast milk is D deficient. Unfortunately, early deficiency can have lifelong consequences.
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