Spilled Milk: New Data Casts Doubt on Vitamin D
The pendulum of medicine has swung again toward reversing some "exciting" research associations that have been generally embraced over the past several years. Now, the sweeping claims of benefit for vitamin D are on the chopping block. I can't say I'm surprised.
I've been through it with other vitamins in my decade and a half long medical career. First was vitamin C. Megadoses were going to prevent illness and cancer with their antioxidant properties. This never panned out. Next, vitamin E was going to prevent Alzheimer's and various cancers. This never panned out. Now, it's D's turn.
The Basis for Prior Claims
In research, the ultimate way to prove something true is the randomized placebo-controlled study. This research pits a therapy against a placebo with a large number of subjects. Does the therapy work better than the placebo? If so, to what degree? The answer to these two questions are as close to a gold standard as it gets.
The trouble with claims on vitamin D lie in the fact that they were not tested in this way, but instead based on observational epidemiology. Associations were seen, claims were made. This was, in hindsight, a bit premature. Following these claims have been some more thorough and rigid tests.
Two separate studies were published last week in the British Medical Journal. Both studies illustrate that random clinical trials do not substantiate the benefits seen in observational vitamin D studies. The most important claims to be challenged regarding vitamin D are reduction of fractures, reduction of falls in the elderly, cancer benefits, and reduction of several diseases including diabetes. According to the researchers, these claims cannot be firmly made based on more rigorous clinical trials.
One claim was proven though - the reduction in tooth cavities in children. But even with this, researchers cautioned that better testing is needed to draw a more definitive conclusion. Nothing was mentioned in these studies about the use of vitamin D in treating mood in the face of seasonal affective disorder and depression.
The Take-Home Message?
It's easy to be once bitten and twice shy about general vitamin claims that getting more than a reasonable daily dose with diet can improve our health. Such claims have been many over the past several years but nearly everything has not held up to more rigid scientific scrutiny. In maintaining strong bones and preventing chronic disease, a healthy diet with enough vitamin D are probably the best. And get a reasonable amount of sun when it is available (even 15 minutes) to help metabolize the vitamin D.
On a final note, I still am taken by the number of people who have told me that they just feel better in mood and energy when they start supplementing vitamin D. Is this placebo or are we missing something here?
British Medical Journal online publication April 1, 2014