Harvard’s Willet on the IOM vitamin D study and then some

Walter Willet, Harvard nutrition researcher and epidemiologist famous for promoting the Mediterranean diet, offers his take down of the IOM vitamin D report today.

The Institute of Medicine report, which reset minimum Vitamin D requirements, concluded that most people get enough through a combination of diet, supplements and sunshine. The report also said there is little evidence of benefit from megadoses.

Willet told the Globe when the finding were “flawed” when they were  announced two weeks ago. Today,  Harvard School of Public Health  tweets notice of his fuller response. In it, states that lack of randomized clinical trial results about higher intakes does not mean lack of benefit. This comment is likely to stir up a debate between those who insist on RCT results and those who say evidence short of that can be strong enough to suggest benefit.

Although benefits of serum concentrations of 25(OH)D higher than 50 nmol/l (20 ng/ml) on endpoints other than bone health have not been documented by randomized trials, the evidence for benefit is quite strong for some, especially colorectal cancer. (6) The IOM conclusion that intakes of vitamin D are adequate for most of the US population assumes that lack of randomized trials means lack of benefit, which seems illogical. 

While the comment clears up Willet’s position, they do little to explain what seem to be conflicting reports on the original study.For example, try sorting out the difference between the Globe and NYTimes stories. Here’s a shot:

The Globe reported:

A long-awaited report from a panel of independent scientists recommends tripling the amount of vitamin D most Americans should take and small increases in calcium levels for children to build and maintain strong bones…

Previous guidelines did recommend 200 units of Vitamin D day for people up to age 50. The new report recommends 600.Whether you need to take Vitamin D supplements to reach that point is the question.  Maybe the word “need” should replace the term “should take.”

For more imprecision, note the second paragraph in the Times story:

The group said most people have adequate amounts of vitamin D in their blood supplied by their diets and natural sources like sunshine, the committee says in a report that is to be released on Tuesday.

Here’s what the report says: While on average, people in North America don’t get enough Vitamin D in their diets, they seem to have enough in their systems. That suggests sun exposure is playing a role. Click here for a PDF summary.

While the average total intake of vitamin D is below the median requirement, national surveys show that average blood levels of vitamin D are above the 20 nanograms per milliliter that the IOM committee found to be the level that is needed for good bone health for practically all individuals. These seem­ingly inconsistent data suggest that sun exposure currently contributes meaningful amounts of vitamin D to North Americans and indicates that a majority of the population is meeting its needs for vitamin D.

In response to a  BHN query, the committee chair and a professor of nutrition at Pennsylvania State University Catherine Ross said, “The blood measurements integrate exposure from diet, supplements and Sunshine, but cannot tell how much from each source.”

So, it seems the Time story should have added “supplements” to that line.


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