Do we really know how much of vitamin D to take?

Call it a dose of reality for doctors who have been pushing high doses of vitamin D.
A new report from the prestigious Institute of Medicine recommends higher doses of vitamin D, but says there's no proof that megadoses of the vitamin prevent cancer or heart disease. In fact, the report says, high levels of the "sunshine vitamin" could be hazardous.

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