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Despite the hype, hard evidence for vitamin D health claims remains lacking

Vitamin D is definitely the celebrity nutrient of the 21st century, but hard evidence to back up the vitamin’s benefits is lacking.
Vitamin D is definitely the celebrity nutrient of the 21st century, but hard evidence to back up the vitamin’s benefits is lacking.

As I’ve noted here before, vitamin D is definitely the celebrity nutrient of the 21st century — the one that keeps popping up in headlines because yet another study reports it may lower the risk for this or that ailment, from the common cold to cancer.

In fact, earlier this month, several yet-to-be-published studies suggesting a positive association between vitamin D and a lower risk of heart disease were presented at an American Heart Association scientific meeting — and dutifully reported by the media.

But, as reporter Michael Smith points out in an article for Medpage Today, there’s a big problem with all this good press: “Hard evidence to back up the vitamin’s benefits is lacking.”

“There’s no data,” Dr. Clifford Rosen, the director of clinical and translational research and a senior scientist at Maine Medical Center’s Research Institute in Scarborough, Me., told Smith. “It’s all weak association studies.”

When it comes to heart disease, for example, there have been no randomized clinical trials (the gold standard of research studies) that show vitamin D reduces heart-disease risk.

One such study — the Vitamin D and Omega-3 (VITAL) trial — is under way, but it’s still recruiting participants, so any findings won’t be known for quite some time.

Right now, promoting strong bones is the only proven health claim that can be made for vitamin D. But as the Institute of Medicine (IOM) pointed out when it issued new vitamin D recommendations last fall (200 to 600 international units daily for most Americans under the age of 70), very few individuals need to take supplements for this purpose.

Most of us (yes, including those of us who live in Minnesota’s northern latitudes) get plenty of vitamin D from our food and from natural sunlight, the IOM stressed.

Some randomized trials have revealed evidence that vitamin D may have beneficial health effects not associated with bone strength, but, as Smith notes, that evidence was produced “mostly as an afterthought”:

“Many of the randomized trials people have heard about were trials designed to look at the effect of vitamin D on fractures and falls,” [said Dr. JoAnn Manson, the lead investigator for the VITAL study and a professor of epidemiology and women’s health at Harvard University], with other effects as secondary outcomes.
It’s in the nature of statistics, she pointed out, that if researchers look at enough outcomes, some will be significant just on the basis of chance.
The vast mass of the evidence for any kind of nonskeletal benefit is observational, and therefore suspect until confirmed by a properly designed, randomized trial, Manson said.
Among other things, a host of confounding factors — obesity, poor nutrition, lack of exercise — might play a role. No matter how carefully an observational study is done, she said, confounding is always possible. “Correlation does not prove causation,” Manson reminded.
She noted that randomized trials have demolished observational evidence many times in the past, notably in the cases of such former fads as beta-carotene and selenium.
According to Rosen, there is reasonable evidence that improved vitamin D status leads to better bone health and some evidence that supplements reduce all-cause mortality in elderly women.
For almost everything else, he said, hard evidence is missing.

You can read Smith’s article on the MedPage Today website.

Comments (6)

  1. Submitted by Bill Schletzer on 11/28/2011 - 10:45 am.

    My eleven-year old daughter’s doctor recommended vitamin D supplements to her based on no evidence of a deficiency. The same doctor on the same day did not make this recommendation for my ten-year old son. The kids were at an annual appointment with their mom, my ex.

    My daughter, an extremely conscientious person, is now worried about it and taking supplements everyday. (I bought her the pills even though I disagree just for the sake of her emotional wellbeing.)

    After some web research, including an AMA article saying that vitamin D supplements were not recommended without a tested-for deficiency, I called the clinic to have the doctor explain this recommendation to me. They refused to let me speak to the doctor without a $50 appointment. The untrained person who spoke to me trotted out various urban myths that she believes about vitamin D and defended the doctor on the theory that doctors are always right.

  2. Submitted by Rachel Kahler on 11/28/2011 - 12:10 pm.

    One of the problems with observational science, particularly in medicine, is the positive selection that’s built into the observation. Until a randomized study is done, none of the claims can be substantiated. Why? Who takes vitamin D? On average, people who take vitamins in addition to what they get from their food and/or (in the case of vit. D), sunlight, are those concerned with their health. Those people are also more likely to take additional steps to keep healthy. Those additional steps confound accurate observation of health benefits from any one thing those people do. It’s not that they’re simply taking vitamin D–they’re probably taking a multi-vitamin, too. And maybe exercising more. Or drinking more water. Or sleeping more. Or all of the above and more. All of those things may individually be beneficial to health or they may provide an observable benefit together.

  3. Submitted by Paul Brandon on 11/28/2011 - 03:18 pm.

    The problem is that while there is good evidence that vitamin supplements effectively cure specific vitamin deficiency disorders, it’s much less clear in the literature that they can cure anything else.
    So, if you have any doubts that your diet contains all necessary nutrients by all means take multivitamins. Beyond that you’re probably making someone else rich.

    And note that ‘nutritional supplements do not need FDA approval, so (unlike drugs) there is no legal requirement that they be proven to be safe and effective.

  4. Submitted by Bernice Vetsch on 11/28/2011 - 03:55 pm.

    I’d guess the reason Vitamin D is good for older women is that it makes it possible for them to utilize the extra calcium they take for bone strength.

    One of the sillier studies I’ve read about is the one that studied the incidence of heart disease between people who took calcium and those who did not. The scientists did not, however, include people in the study who took Vitamin D, without which the calcium (or at least much of it) would be secreted or would end up in their blood.

  5. Submitted by Henry Lahore on 11/28/2011 - 07:34 pm.

    The have been scores of excellent random controlled trials and meta-analysis of studies with vitamin D.
    And currently there are over 100 studies of vitamin D intervention and cardiovascular disease, for example

  6. Submitted by Joel Gingery on 11/28/2011 - 09:05 pm.

    Criticize vitamins and other supplements all you want, but vitamin D saved my marriage! My wife was diagnosed with seasonal affective disorder (SAD) many years ago. At the time, the only treatment was use of a light box every morning, which was suppose to simulate summer sunlight. It didn’t work, and every fall she would talk about dreading the approaching darkness of winter. By mid-February she was deeply depressed. The depression lifted dramatically on trips to sunny locales, but it returned as soon as the plane descended onto the MPLS-SP airport.

    After decades of living this way, she found a psychologist who recommended trying vitamin D. My wife had her blood level checked, which confirmed a severe deficiency. She began taking 2,000 IU in the fall and felt somewhat better. Then she doubled the dose and experienced a dramatic improvement–the depression completely lifted. My kids had their mother back, and I had my wife back. She continues to take vitamin D every fall and winter. Her blood level remains in an optimal range.

    Relocating to Florida was not an option. Taking a supplement proved to be an easier and less expensive solution. I don’t need scientific studies to confirm our personal experience.

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