Sorting out the vitamin D story needs better data, not religious fervor

If even a tenth of what's being said about vitamin D these days is true, those of us astute enough to supplement what we get from the sun are destined for a ripe old age.  Or, if we're already old, and female, taking vitamin D might extend our lives even further.

The idea that vitamin D promotes bone density is based on solid evidence, but beyond that it's effectiveness is not entirely clear.  Advocates say that vitamin D prevents prostate, breast and other cancers, multiple sclerosis, diabetes, heart disease, osteoporosis, allergies, inflammation, fights the common cold and the flu, and boosts fertility, just to name a few of the benefits being touted.  And, limited sun exposure for mothers during pregnancy could be condemning children to a lifetime of illnesses.  According to a new study,

We have known for some time that mums-to-be with low vitamin D levels during pregnancy run the risk of having ­a child that may develop diabetes.

This latest study concluded that other conditions like asthma, autism, multiple sclerosis (MS) and Alzheimer’s could be related to low levels of maternal vitamin D.

Yes, Vitamin D is "Summer's Superhero"!

“Vitamin D deficiencies are rampant amidst our nation and could possibly lead to an increase in the most troubling diseases of our time,” said Steven Hotze, M.D., founder and CEO of PPVS [Physicians Preference, vitamins and supplements].

Indeed, Mozart may have died of vitamin D deficiency!  Think what music the world is missing because he slept during the day when he should have been sitting in the sun, and composed and caroused all night.

Well, how much of this hype is actually true?   And how would we know?  A Nature News Feature published online on July 6 details an ongoing debate on this question.  Recent recommendations have been that we are all vitamin D deficient, and should be boosting our vitamin D with sometimes megadoses of D3 supplements.  Naturally, many scientists who've been researching this subject now have vested interests in plugging supplements, and, as always, this makes it harder to separate the wheat from the chaff.

In response to all the hype, an 'expert panel' was convened by the Institute of Medicine (a non-profit affiliated with the US National Academy of Sciences) to soberly assess the evidence and make recommendations about healthy vitamin D levels, and who should be taking supplements.  They issued their report last November saying that vitamin D levels recommended by current conventional wisdom were too high, and in fact could even be harmful.  But the report has not gone down easily; panel members have been sent abusive and threatening emails, and so on.  As Nature says,

Much is at stake. By 2009, the amount spent on vitamin-D supplements in the United States had risen tenfold in ten years (see 'Raising the stakes'). Medical practitioners and public-health officials worldwide look to the IOM for guidance on how to interpret the conflicting claims about vitamin D. Yet several vitamin-D proponents say that the IOM's methods, which involved a systematic review of the literature, were flawed. They have accused the panel of misinterpreting data and over-emphasizing the danger of heavy supplementation. Just last month, the Endocrine Society, a professional association of 14,000 researchers and clinicians based in Chevy Chase, Maryland, released guidelines that recommend higher doses than the IOM did.

Why, instead of clearing confusion as was the IOM's goal, has the report sown division and unrest? "The IOM was too definitive in its recommendations," says Michael Holick, an endocrinologist at Boston University School of Medicine in Massachusetts, and an outspoken critic of the IOM panel's conclusions. "Basically, the vitamin-D recommendations are based on low-quality evidence," says Gordon Guyatt, a clinician researcher at McMaster University in Hamilton, Ontario, who has been a consultant on various guidelines. "I think admitting that would have made some of the angst disappear."

(For the record, Holick is not only an outspoken critic of the IOM recommendations, but he has been one of the leading drivers of the vitamin-D-cures-all train for some time, and has a lot to lose if it turns out he has been wrong.)

Indeed, many observers, interested and disinterested alike, recognize that there's a lot of questionable science in the vitamin D field.  It's hard to figure out how recommended levels have been set, there have been few if any prospective studies starting with a cohort of healthy people and following them forward, and many that look at vitamin D in people who are already ill.  Such studies are confounded by the fact that people who are ill tend to stay indoors, out of the sun and thus not synthesizing vitamin D, so it's not possible to know whether the vitamin D deficiency (deficiency according to current standards, however they were determined) preceded and thus led to the illness, or was a result.  Many studies have too few subjects for results to be robust, and so on.

Members of the now disbanded IOM panel are calling for large, multi-year prospective studies, in recognition of the fact that much of the data are from studies that are less credible than they should be.  But this too has generated heated dissent.  As the Nature piece says,

Perhaps IOM panel members underestimated the passion present in the vitamin-D field. Physicians who recommend high doses of vitamin D might not want to believe that the evidence they have trusted isn't quite up to par. "One thing I wasn't aware of before, is the tremendous pressure from industry and investigators who are tied to their religious belief in vitamin D," says Rosen.

So given all of this, why would one ever think of pouring more research funding down this sink-hole, to identify the obviously minor if not trivial effects over which these debates are centered?  Clear vitamin D deficiencies are not at issue.

Several years ago, we did an extensive review of the vitamin D literature and we, too, were unassailably convinced that most conclusions, from recommended blood levels to the diseases caused by deficiencies, were based on questionable to poor data.  As far as we could tell, basic questions are still unanswered, including almost everything about mechanisms of action.  This is another instance of correlations being assumed to be causation without biological justification.

To put it bluntly, the idea that we are all vitamin D deficient is manifest, blatant biological, and evolutionary clap-trap.  It is at the very least extremely naive and superficial thinking.  We live hugely longer and in better health than our ancestors did, when natural selection--to the extent that it cared--established the required levels for successful survival and reproduction.  So the assertion of pandemic deficiency really can mean no more than that we might be somewhat better off, or live even longer, if we doped up on the advocates' dietary supplements.  Such panacea talk is not new to human society, but in an age of science should be roundly stamped out, because it is misleading.