D in Science

Google searches for Hypovitaminosis D
Google searches for Vitamin D
My astute friend Lia asked me what is up with Vitamin D. And indeed, sales are up (by about 1000% over the course of the 2000s), and Google searches are up (by a factor of about 4 since 2004 on both Vitamin D and Vitamin D Deficiency). In the last 10 years or so, physicians have been increasingly telling people they are vitamin-D-deficient and recommending Vitamin D supplements. Lia wanted to know if vitamin D deficiency is a real problem or a fake one.
To cut to the chase, it’s a fake one: another giant detour into the dark alley of pseudo science, another example of Ben Goldacre’s dictum, “Without anybody’s noticing it, bullshit has become an extremely important public health issue.”
An article published in 2009 found that from 1994 to 2004 the proportion of Americans who had adequate Vitamin D fell by half. Scientific American reported the news, along with a skeptical view from a disinterested government expert, who pointed out that over half of the change was due to a change in testing methodology. The New York Times’ Jane Brody also reported the news, along with an over-the-top endorsement of an expert who has taken money from the tanning industry and —coincidentally?— also posed on a tanning bed in a USA Today interview to promote Vitamin D intake.
If you look to the internet you’ll find plenty of serious-sounding people who have mastered vocabulary words like metabolites and calcifediol. Usually these doctors — inevitably they are doctors — have a side business selling supplements, and they are convinced that daily intake of vitamin D should be three times as large as that recommended by the Institute of Medicine. One site, whose motto is “Call Toll Free”, features a doctor who advocates a daily dose 10 times higher than that recommended by the IOM.
So much for internet quacks, but what about your own doctor? These harried folks don’t have the time or energy to follow the curvaceous lines of science as it wends its leisurely way to the truth. They send out to labs, who test your blood, and provide answers couched in terms of “normal” or “deficient.” But there is no standard for what counts as deficient, and different labs choose different cut-offs. If your doctor says your blood is vitamin-D deficient, most likely it isn’t your doctor speaking: it’s the lab.
A comprehensive review by the Institute of Medicine in 2010 concluded that Vitamin D is important for bone health, but not for any other health conditions. The report concluded that levels above 20 nanograms per milliliter are adequate “for practically all individuals,” but that many labs telling people they are deficient at 30 nanograms per milliliter. That’s a big difference, especially because the report says that levels above 50 nanograms per milliliter can be toxic.
A systematic review published in 2014 found that vitamin-D supplementation resulted in no improvement in health outcomes for most people. The study concluded by noting that illness causes low vitamin D status, which accounts for the association between low vitamin D and illness that is driving Jane Brody and your lab into paroxysms.  An accompanying editorial pointed out:
Supplementing at high doses could cause harm in people with already high concentrations of serum vitamin D, particularly in those with liver, kidney, or vascular problems. This is a concern, given the large number of people taking vitamin D supplements (up to 50% of adults in the USA).
As the evidence against Vitamin D supplementation continues to build, sales continue to rise. The Council for Responsible Nutrition—a deceptively named trade group of the supplement industry—disagrees with the expert analyses of the Institute of Medicine and the US Preventive Services Task Force. But unless you’ve got stock in supplement-manufacturers, you don’t need to.
The bigger lesson is that just because the doctor says you’re Vitamin D deficient doesn’t mean it’s true. Physicians know a great deal about illness and very little about health.
I’ve said it before, and I’ll say it again: the most important public health question is: What to Believe?

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