This is a solid piece on TheScientist online.
Subhead: “Prevention trials for vitamins and supplements are notoriously difficult, but some researchers aren’t giving up on finding proof that vitamin D helps ward off disease.”
And it seems the public isn’t waiting for clinical trial data. Spurred by headlines about its potential benefits, US consumer sales of vitamin D supplements rocketed from $50 million in 2005 to $550 million in 2010, according to estimates from the Nutrition Business Journal. Enthusiasm for the vitamin echoes among doctors and natural-food advocates, who are pushing for doses higher than the 400 to 600 International Units (IU) that the government currently recommends for maintaining healthy bones.
However, (epidemiologist JoAnn Manson at Harvard Medical School), a refined woman of measured words, is acutely aware of the disappointment that has trailed the hyping of vitamins over the decades. Vitamin E, a fat-soluble antioxidant, gained a reputation for fighting cancer in the 1990s, when observational studies found that people who took supplements had lower rates of the disease. But the buzz died out in 2008 when a 35,000-person clinical trial on vitamin E and selenium was terminated prematurely after people taking the supplements showed a slightly higher risk of developing prostate cancer than the control group. Similarly, in 1996 two large clinical trials dumbfounded fans of beta-carotene, a substance that humans convert into vitamin A after consuming it in fruits and vegetables. One trial found that it raised the risk of lung cancer and heart disease, and the other ended anticlimactically after 12 years with the conclusion that beta-carotene supplements performed no differently than placebo. “You have to look at these previous randomized trials as cautionary tales,” Manson says, “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.”
Towards the end of a wonderfully-detailed piece, there is this chart that could be a reminder for many journalists on the pitfalls of many studies.
Potential trial pitfalls
Critics of vitamin D trials worry about the following drawbacks common to prevention trials of nutrient supplements.
- Dose too small
- Dose too risky
- Outcomes too uncertain (an increased risk of disease, rather than the disease itself)
- Too little time
- Too few participants
- Incorrect treatment regimen
- Poor compliance
- Cherry-picked participants