Report: A bit more vitamin D is good, not too much

Tempering the cure du jour madness.

Got milk? You may need a couple 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 — 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 put some brakes on the nation's vitamin D craze, 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...

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.

Yep.