Report: A bit more vitamin D is good, not too muchWASHINGTON — New U.S. dietary guidelines recommend more doses of vitamin D than under the current standards, but caution that there’s no proof that megadoses prevent cancer or other ailments.
By: Lauran Neergaard, Associated Press
WASHINGTON — New U.S. dietary guidelines recommend more doses of vitamin D than under the current standards, but caution that there’s no proof that megadoses prevent cancer or other ailments.
The decision by the prestigious Institute of Medicine, the health arm of the National Academy of Sciences, could put some brakes on the current vitamin D craze in the U.S., warning that super-high levels could be risky.
“More is not necessarily better,” cautioned Dr. Joann Manson of Harvard Medical School, who co-authored the Institute of Medicine’s report being released Tuesday.
Most people in the U.S. and Canada — from age 1 to age 70 — need to consume no more than 600 international units of vitamin D a day to maintain health, the report found. People in their 70s and older need as much as 800 IUs. The report set those levels as the “recommended dietary allowance” for vitamin D.
That’s a bit higher than the target of 400 IUs set by today’s U.S. government-mandated food labels, and higher than 1997 recommendations by the Institute of Medicine that ranged from 200 to 600 IUs, depending on age.
But it’s far below the 2,000 IUs a day that some scientists recommend, pointing to studies that suggest people with low levels of vitamin D are at increased risk of certain cancers or heart disease.
“This is a stunning disappointment,” said Dr. Cedric Garland of the University of California, San Diego, who wasn’t part of the institute’s study and says the risk of colon cancer in particular could be slashed if people consumed enough vitamin D.
“Have they gone far enough? In my opinion probably not, but it’s a step in the right direction,” added prominent vitamin D researcher Dr. Michael Holick of Boston University Medical Center, who said the new levels draw needed attention to the vitamin D debate and encourage more food fortification.
Vitamin D and calcium go hand in hand, and you need a lifetime of both to build and maintain strong bones. But the two-year study by the Institute of Medicine’s panel of experts concluded research into vitamin’s D possible roles in other diseases is conflicting. Some studies show no effect, or even signs of harm.
A National Cancer Institute study last summer was the latest to report no cancer protection from vitamin D and the possibility of an increased risk of pancreatic cancer in people with the very highest D levels. Super-high doses — above 10,000 IUs a day — are known to cause kidney damage, and Tuesday’s report sets 4,000 IUs as an upper daily limit — but not the amount people should strive for.
And Manson pointed to history’s cautionary tales: A list of other supplements — vitamins C and E and beta carotene — plus menopause hormone pills that once were believed to prevent cancer or heart disease didn’t pan out, and sometimes caused harm, when put to rigorous testing.
To help settle the issue, Manson is heading a government-funded study that’s recruiting 20,000 healthy older Americans to test whether taking 2,000 IUs of vitamin D really will lower their risk for heart disease, a stroke or certain cancers.
In the meantime, it’s hard to consume 600 IUs of vitamin D from food alone. A cup of D-fortified milk or orange juice has about 100 IUs. The best sources may be fatty fish — some servings of salmon can provide about a day’s supply. Other good sources are D-fortified cereals.
But here’s the report’s big surprise: While some people truly are seriously deficient in vitamin D, the average person in fact already has enough circulating in his or her blood — because we also make vitamin D from sun exposure, and because many people already take multivitamins or other D-containing dietary supplements.
EDITOR’S NOTE — Lauran Neergaard covers health and medical issues for The Associated Press in Washington.