WASHINGTON — You may need a couple of extra cups of milk 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 — sure to frustrate backers of the so-called sunshine vitamin.
The decision by the prestigious Institute of Medicine, the health arm of the National Academy of Sciences, could slow the nation's vitamin D craze, warning that super-high levels could be risky.
"More is not necessarily better," cautioned Joann Manson of Harvard Medical School, a doctor who co-authored the Institute of Medicine's 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 IUs. The report set those levels as the "recommended dietary allowance" for vitamin D.
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That's a bit higher than the target of 400 IUs set by today'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.
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.