A raft of laboratory and clinical data gathered over the last ten years has suggested that Vitamin D has a protective effect against our getting cancer. Clinicians have made the measurement of Vitamin D levels part of the extended annual physical. Women and some men are place on Vitamin D supplementation with the goal of improving bone health and, more recently, preventing cancer. So what are we to make of a recent study that suggests that giving Vitamin D to prevent cancer is a waste of time?
In the Journal of the American Medical Association is a study by Lappe and colleagues from Creighton University in Omaha, home of Dr. Henry Lynch, discoverer of the eponymous Lynch Syndrome, or hereditary non-polyposis colon cancer. Click here for the abstract. Dr. Stark can send you the full article. Just request it by going to the box to the right. Anything from Creighton on cancer epidemiology therefore is taken seriously. What the authors did was take over 2300 healthy postmenopausal women and give half of them calcium and Vitamin D supplementation. They measured Vitamin D levels serially and looked at the incidence of new cancers in the two groups. They found a 30% reduction in incidence of new cancers in the group that took Vitamin D over the four years of observation but this difference was not statistically significant. There was no particular type of cancers where the prevention was more robust. The authors concluded that Vitamin D and calcium supplementation does not prevent cancer.
Dr. Stark weighs in: Shame on JAMA for publishing this article. First of all, mean Vitamin D levels in the controls was high normal, not reflective of the state of the average post-menopausal woman in the non-tropical US. Why? The authors don’t state or don’t know. Any preventive measure like this should have a deficiency in the control group. Second, there was a 30% reduction in incidence. Had the authors done a larger study, it is likely that this magnitude of difference, if maintained, would have reached the magic p < 0.05. Third: the period of observation is four years, arguably much too short for cancer prevention. Finally the authors don’t state when Vitamin D levels were measured. There is a huge difference in levels measured at the end of winter vs. the end of summer, as reported by Tangpricha et al So from my perspective this paper, reported in a very widely read and well respected journal, is a non-event.