The controversy over vitamin D will never end, because the "gold standard" of two double-blind placebo-controlled studies for each of its myriad indications will never be carried out. It's impractical or, depending on where you live, impossible to get enough but not too much vitamin D from sun exposure; so you probably need to take this particular supplement. Get a vitamin D test if you can, but whether or not you do, it's a good idea to supplement with D on those days you're not getting at least 20 minutes of sun exposure over 80% of your body (i.e., in shorts and a tank top outdoors under a sunny sky between 10 a.m. and 2 p.m. at most latitudes). That's my spiel, the one I reel out to all comers. Of course I run into skeptics. Behind my chin music there’s a ton of scientific evidence, but you’ve got to respect doubt. After all, this industry—the whole health and wellness shebang—runs mostly on fumes of hope and clouds of hype, which are wont to dissipate. For years, eggs, margarine, wine, the list goes on, are “bad for you”, and then one fine morning you wake up to find that they’re “really” good for you, or is it the opposite? Isn’t it better to wait for the dust to settle as scientists duke it out? It depends on your point of view.
In the late 1950s, doctors saw high rates of birth defects in babies of mothers who’d taken a morning-sickness drug recently launched by a German company. In 1962 it was withdrawn from the market (and later reintroduced as a cancer treatment), but the thalidomide crisis caused an enduring shift in risk-benefit calculations. The risk of approving a drug that could cause harm came to be seen as more serious than the risk of preventing a potentially beneficial treatment from reaching patients. Notice the lopsided “risk landscape”: approving a potentially harmful drug could harm patients, as well as derail the approver’s career; but disapproving a potentially beneficial drug could also harm patients (by withholding a cure), but won’t derail the disapprover’s career. A “no” might even make you a hero: in 1962 Dr. Kesley, the FDA pharmacologist who had blocked thalidomide from the U.S., received a President's Award for Distinguished Federal Civilian Service from President Kennedy; in 1995 a German astronomer named an asteroid after her; and in 2010, after she retired at age 90, the FDA named a medal after her—not bad for a Canadian from Cobble Hill, British Columbia. The problem is that since Dr. Kesley’s honorable “no”, there has been more political pressure to disapprove than to approve drugs; and around the world, this “it depends”, “more research is needed” pressure is drawing dietary supplements into the government’s paternalistic purview.
For drugs, this lopsided balance of power was rectified somewhat in the 1990s by AIDS activists. Patients basically told the government, “I’m going to die, I’ll take my chances with this experimental drug, thanks. I don’t need your approval” which approval might take years as drug companies carry out clinical trials and FDA reviews the results. With regards to vitamin D and its purported anti-cancer effects, the problem is that there is no end to this “it depends” , no way to move from “purported” to “proven.” More research is always needed. A UN advisory council, tasked with studying vitamin D and cancer, prevention called for—wait for it—“more research”: a pivotal clinical trial that would cost upwards of $100 million, take decades to carry out—and almost certainly will never happen. If you’re a government regulator, it might be your job to say “it depends”, “more research is needed” when faced with claims that dietary supplements can help reduce the risk of disease. If you’re a private citizen, it’s up to you to decide. At least it still is, most places.
If you hop on to the vitamin D bandwagon at 2,000 to 10,000 IUs a day (depending how much sun you get), you’re risking wasting money if all this is later shown to be horse hockey. If you’re low in magnesium, you might have higher risk of kidney stones or leg cramps. The smart thing is to make sure you’re getting enough magnesium—eat sunflower seeds or take a supplement. The risks of taking “high-dose” vitamin D (higher than the IOM’s recommended 600 IU/day, but no higher than the Council for Responsible Nutrition’s Upper Limit for Supplements for vitamin D of 10,000 IU/day) are minimal or nil. Yet in its recent review of vitamin D, the Institute of Medicine not only failed to substantially raise the recommended daily amounts, it actually lowered the threshold for deficiency. At one stroke of a bureaucrat’s pen, millions of people no longer needed to supplement with vitamin D, because they were no longer deficient.
I say nuts to that.
Against the risk of supplementing, you have to weigh the risk of not supplementing, which, population studies suggest, would expose you to a higher risk of cancer. Population studies aren’t as definitive as controlled clinical trials. But if you wait for definitive answers in this field you’ll die with your questions still unanswered, with or without cancer. “No great deed is done by falterers who demand certainty,” said the novelist George Eliot. Popping a vitamin D pill is not a great deed, it’s a simple, small, individual decision of a free person. Whether doing so is worthwhile depends on your point of view, and your weighing of the pros and cons on either side of the question.