New vitamin D guidelines warn against megadoses

By Lauran Neergaard

WASHINGTON — Got milk? You may need a couple of cups more than today's food labels say to get enough vitamin D for strong bones. But don't go overboard: Long-awaited new dietary guidelines say there's no proof that megadoses prevent cancer or other ailments.

The decision by the Institute of Medicine, the health arm of the National Academies, could put the brakes on the nation's vitamin D craze.

"More is not necessarily better," cautioned Dr. Joann Manson of Harvard Medical School, who co-authored the report, being released today.

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 units. The report sets those levels as the "recommended dietary allowance" for vitamin D.

That's a bit higher than the target of 400 units set by today's government-mandated food labels, and higher than 1997 institute recommendations that ranged from 200 to 600 units, depending on age.

But it's far below the 2,000 units 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 study and who 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 that research into vitamin D's 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 highest D levels.

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 units 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 units of vitamin D from food alone. A cup of D-fortified milk or orange juice has about 100 units. The best source may be fatty fish — some servings of salmon can provide about a day's supply. Another good source is D-fortified cereals.

And here's the report's big surprise: While some people truly are seriously deficient in vitamin D, the average American 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 supplements.

source: http://www.statesman.com