by Robert P. Heaney, M. D., The John A. Creighton University Professor and an internationally known expert on vitamin D, osteoporosis, and human calcium physiology.
The U.S. Preventive Services Task Force (USPSTF) last week made recommendations that have rained on the parade of those of us trying to optimize our health with vitamin D supplements. Or so it would seem. The recommendations said most of us shouldnít take vitamin D supplements toward preventing cancer or bone fractures. I disagree.
Remember the Task Force is a very conservative group Ė by design Ė and is mostly concerned not with nutrients, but with medical interventions, particularly diagnostic tests such as mammograms and prostate cancer screening. Itís relatively straightforward to evaluate the effectiveness of medical tests. You look at the outcome in individuals who have had the tests and compare them with those who havenít (the control group). But with nutrients like vitamin D, itís another question entirely, since there is no true control group. Everybody gets some of every nutrient, and so the question is not whether a particular nutrient is efficacious, but how much must we have to ensure optimal health.
In its current set of recommendations the Task Force stated that they couldnít find enough evidence to evaluate the balance of possible risks and benefits from vitamin D supplementation for two outcomes: cancer and fractures. I believe our studies at Creighton University indicate there is enough evidence to say that vitamin D supplementation does help prevent factures and protects against some cancers. Whether or not such evidence exists, itís important to note that USPSTF had previously recommended vitamin D supplementation for the prevention of falls in older adults, and they restated that recommendation in this most recent release. The new recommendations on cancer and fractures are moot, because individuals already taking the vitamin D needed for the prevention of falls will automatically get whatever cancer and fracture benefit there may be.
So itís important to understand that USPSTF is not really recommending against our taking vitamin D supplements. Theyíre saying, instead, that they canít be sure how far reaching the benefits might be.
Another note of caution. The Task Force work assumes that weíre all the same. A study that failed to find an average effect greater than one would expect from random chance alone, is deemed ďnegativeĒ. But the samples studied may well have contained, for example, a small group of individuals who responded strongly to the intervention, while the majority didnít respond at all. The Task Force doesnít look at whether it works in some individuals; but instead what may be the balance of risks and benefits for the whole U.S. population. With mammograms or prostate cancer screenings, for example, there is the downside risk of radiation and surgical damage, affecting everybody, even those who didnít have a cancer and would have done perfectly well without the screening test. Weíre all grateful for the power of medical technology, but we have come to recognize that its use carries dangers as well as benefits.
Fortunately thatís not much of an issue with nutrients. So, if only one-fourth of the population benefits from extra vitamin D (but we donít know which fourth that is), the real question is does the extra vitamin D hurt the other three-fourths who get no benefit?
The Task Force said it didnít know.
Unfortunately, none of the 17 members of the Task Force is an expert in vitamin D biology and perhaps they can be excused for being unaware of the fact that the levels of vitamin D commonly being used today barely reproduce what our grandparents got from greater time outdoors (let alone what would have been the vitamin D intake of early humans living in East Africa, where one got vitamin D mainly from the sun, year round). The safety profile of vitamin D is actually very good, so long as one does not exceed the tolerable upper intake levels promulgated recently by the Institute of Medicine (4,000 IU/d) or the Endocrine Society of the United States (10,000 IU/d).
Should we all stop taking vitamin D? My family and I donít plan to.