Earlier this year, the U.S. Institute of Medicine upped their official vitamin D recommendation for most adults from 200 to 600 IU a day. Where did they get the original number, why did they triple it, and why are there those who recommend people take thousands a day rather than hundreds?
Though the IOM report has been considered "the most comprehensive document on vitamin D nutrition to date," it raised intense controversy in the scientific community, culminating with the publication of conflicting guidelines recommending 1,500-2,000 IU a day from the American Endocrine Society, the world's oldest, largest, and most active organization devoted to hormone research ("vitamin" D is a misnomer; it's actually a hormone).
When even the consensus committee expert panels disagree, where can you turn? Ideally, the answer is the primary source literature, but this is no small task given that more than 3,000 new journal articles were published on vitamin D in the last year alone. This last week of NutritionFacts.org videos has been my attempt to provide justification for my own vitamin D recommendation based on my understanding of the best available science.
In Vitamin D Recommendations Changed, I start out by explaining the rationale behind the Institute of Medicine's change of heart. In Evolutionary Argument For Optimal Vitamin D Level the IOM's target blood level of vitamin D is questioned (given the fact that we evolved running around naked in equatorial Africa). The Institute of Medicine's conservative position on vitamin D is understandable, though, given the history of hyped vitamin supplements that turned out worthless or worse, as I review in Is Vitamin D the New Vitamin E?
The official vitamin D recommendation is based on bone health, as the IOM considers the extraskeletal benefits unproven. Others cite evidence that taking 2,000 IU a day may reduce "risk for autoimmune diseases; deadly cancers including prostate, colon, and breast cancer; type II diabetes; heart disease; cognitive dysfunction; and infectious disease." I jump straight to overall mortality in Vitamin D and Mortality May Be a U-Shaped Curve, suggesting that both too little and too much may adversely affect longevity.
Why not just rely on the sun? Vitamin D Supplements May Be Necessary sheds light on the fact that even under optimal sun exposure, many people will not reach circulating D levels associated with the lowest overall mortality. Everyone responds differently to supplements, though, making it challenging to formulate one-size-fits-all guidelines, as shown in The Difficulty of Arriving at a Vitamin D Recommendation.
How the Institute of Medicine Arrived at Their Vitamin D Recommendation shows how they used the body's own reaction to protect bone health to come up with their guidelines, whereas yesterday's video-of-the-day, Resolving the Vitamin D-bate, extends that logic to tap into the entire body's innate wisdom. This morning, the series concludes with Take Vitamin D Supplements With Meals, suggesting a cost-effective strategy to achieve optimum levels.
I realize that I may have gone into more background detail than was necessary for many viewers, but I just don't feel comfortable handing down some decree. Particularly given the contentious nature of the issue, I wanted to systematically lay out the reasoning behind my current advice.
-Michael Greger, M.D.