Like hemlines, nutrients are subject to the whims of fashion. Lately, Vitamin D has taken center stage.

In excerpting a piece originally posted on The Scientist, Health News Review recently noted that U.S. consumer sales of vitamin D increased fivefold from 2005 to 2010. Caregivers are embracing doses higher than the 400 to 600 International Units (IU) the government recommends for maintaining healthy bones.

Readers of MedPage Today are largely medical professionals and people interested in their affairs—health media, the pharmaceutical and medical device industries, health-care administrators and insurers, as well as interested medical consumers. A recent poll of those readers confirmed the vitamin’s popularity. Most respondents were certain that supplementing one’s diet with vitamin D and calcium was a good idea.

Given the sketchy evidence, you have to wonder why.

As The Scientist article noted, hype is a constant companion to nutrient/supplement claims. Vitamin E’s anti-cancer properties were undermined by a 35,000-person clinical trial that was terminated prematurely after people taking the supplements showed a slightly higher risk of developing prostate cancer than the control group. Large clinical trials studying beta-carotene and its conversion into vitamin A found an increased risk of lung cancer and heart disease.

Said one Harvard Medical School epidemiologist, “You have to look at these previous randomized trials as cautionary tales because they show that time and time again, everyone jumped on the bandwagon and then the randomized trials did not have favorable results, and in fact, the risks outweighed the benefits.”

We broached this topic a while ago.

Under some circumstances, according to a new study, high doses of vitamin D do seem to prevent bone fractures among the elderly. (That study, however, was unable to determine the role of calcium, which its participants also took, and which could be a critical component of the benefit.) And last month, the U.S. Preventive Services Task Force said that, contrary to popular belief, low doses of vitamin D and calcium do not reduce the risk of bone fractures for older women. It also found insufficient evidence that higher doses protect the bones of postmenopausal or premenopausal women, or reduce the risk of cancer, which are among the reasons people give for taking them.

More than half of the 1,686 MedPage Today survey respondents said they would advise patients to take both supplements, although nearly 1 in 3 said no vitamin or mineral supplementation was necessary if patients ate a balanced diet.

Comments among respondents included advice to eat calcium-rich foods, and take small doses of calcium supplements as well as vitamin D; that eating sufficient amounts of vitamin- and mineral-rich food is difficult because their nutritional value has declined substantially before food is served; that only a particular form of vitamin D is beneficial.

It all speaks to the notion that people are routinely vitamin D deficient, because of poor diet, insufficient sunlight, winter, sunscreen … take your choice.

People with certain disorders do need nutritional supplementation, and some people are vitamin deficient. But it’s not a blank-check situation. The nutrient to be supplemented and the amount necessary depend on the disorder, the patient’s diet and other medications taken.

But as noted in a story on NPR, vitamin D deficiency is hardly a scientifically proven problem in the U.S., and the task force’s recommendations reflect reality more than fear.

The task force didn’t rule out that higher doses might confer some benefits, but there’s no question that they present certain risks. Kidney stones is one. The risk is small, but is that excruciating pain worth it for an otherwise healthy person who downs a couple supplements as poor-diet insurance?

At high doses, vitamin D can be toxic, and prompt nausea, vomiting, muscle weakness, dehydration and constipation.

Many of the MedPage survey respondents dismiss most vitamin D studies because, they claim, the doses were too low. They say the higher levels that would confer benefits are similar to what the human body would make from sun exposure.

Maybe. But we’re circling back to the original concern: Are doctors and patients misled into thinking there’s an epidemic of vitamin D deficiency whose putative solution potentially disposes healthy people to risk?

No one can draw solid conclusions about whether to take vitamin D, and how much, as noted on Health News Review, until studies address the factors related to prevention trials of nutrient supplements:

• Doses are too small.
• Doses are too risky.
• Outcomes are too uncertain (an increased risk of disease, rather than the disease itself).
• The study period is too short.
• There are too few participants.
• The treatment regimen is incorrect.
• Participants are not random, but cherry-picked. participants.
• There’s poor participant compliance.