GUEST POST BY DAVID MARK
The Washington Post recently published an article asserting that vitamin D is shaping up to be the nutrient of the year, if not the decade. The article started factually strong but weakened at the end when it made specific recommendations.
The Post references an article in Consumer Reports titled “Most people get insufficient Vitamin D, but extra supplements may not be needed.” That article correctly notes that vitamin D blood levels in U.S. residents are on average below what is now thought by some experts to be what is needed for optimal health; the magazine perhaps overstates the case by writing that “…77% of Americans have insufficient amounts.”
In an article published last year in the American Journal of Clinical Nutrition, Elizabeth Yetley uses NHANES data to show approximately 6 percent of adults are below the traditional cut-off defining vitamin D deficiency and 77 percent are below what some nutritionists now opine to be the preferred target of 80 nmol/L.
The Consumer Reports article also points out what is putting the U.S. population at risk, primarily increases in obesity (fat sequesters some of the vitamin D synthesized in the skin) and less skin exposure to sunlight’s ultraviolet radiation.
The Institute of Medicine is currently reviewing the Dietary Reference Intake value for vitamin D, which was last updated in 1997. A final report is expected this May. Currently, people 19 to 50 years of age are advised to consume at least 200 International Units per day, those 51 to 70 at least 400 units, and those over 70 at least 600 units. Estimates are that adults get 100 to 150 units daily from food.
Consumer Reports goes astray when it writes: that people don’t need a special supplement; that overdosing is unlikely; and who should be advised to have their blood levels tested. Although makers of nutritional supplements are planning reformulations of their multivitamin products pending the institute’s report, most of what is on the shelves now is still at only 400 units.
What defines overdosing is up in the air. Officially, the Tolerable Upper Intake Level is 2,000 International Units per day. While bets are that the Institute will raise the adequate intake to 1,000 units per day, it is less clear whether the upper limit will also be increased. Writing in the American Journal of Clinical Nutrition, John Hathcock and his colleagues make a case for 10,000 units as a safe limit. The Institute has a conservative approach to upper limits.
Finally, people should not wait to get a blood test until they are diagnosed with weak bones or an absorption problem, contrary to what Consumer Reports says. Better advice would be for all adults to start taking 1,000 units per day from supplements. If you are in a higher-risk group for low vitamin D levels (obese, female, older, bypass surgery, Hispanic, African-American), get tested a few months later.
David A. Mark, Ph.D., is president of dmark consulting LLC, a science consulting company serving the dietary supplement and functional food industry. Contact him at firstname.lastname@example.org or 978-897-0890.