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BLOG: June 2007

Vitamin D and cancer

Is your low vitamin D level you are not aware of increasing your risk of cancer? Even if vitamin D cancer preventing ability is steadily indicated over decades in a number of (mostly animal) studies, as well as by statistical data, the answer still sounds much like: "Yes, but...".

A recent 4-year study at Creighton University in Omaha, on nearly 1200 women from eastern Nebraska over the age of 55, found that those receiving regular calcium+vitaminD3 supplementation (1450mg and 1100I.U. daily, respectively), had

two and a half times lower cancer incidence rate than those
taking placebo.

The third group, taking calcium only, had nearly two times lower incidence of cancer than the placebo group (Lappe, American Journal of Clinical Nutrition).

While main focus was on the effect of supplementation on hip fracture incidence, cancer-related numbers were too good to ignore. The study conclusion is that "improving calcium and vitamin D nutritional status substantially reduces all-cancer risk in postmenopausal women".

 Media articles, however, seem to be putting main accent on vitamin D and its cancer-preventing ability. What the study numbers imply is just the opposite: it is calcium supplementation that resulted in most of the beneficial effect, with the addition of vitamin D only somewhat improving upon it.

What makes it harder to draw specific conclusions is another recent study, at Harvard, published just week earlier (Lin, journal Archives of Internal Medicine), in which the beneficial effect of high calcium and vitamin D supplementation in a 10-year period benefited only a group of 10,578 premenopausal women in reducing the risk of developing breast cancer by 39% and 35%, respectively. There was no benefit of supplementation for the 20,909 postmenopausal women, which is in direct contrast with the Omaha study.

While the latter study  is more reliable in that the supplemental intake was directly controlled (instead of being reported in the larger, Harvard study), the discrepancy makes either result doubtful. It also reminds that no study result, even when coming from those conducted to high professional standards and in good fate, are not necessarily correct.

What we do know is that vitamin D is, among other functions, necessary for proper functioning of the immune system - particularly the part in charge of warding off infections - and that is needed for proper cell formation and proliferation. That alone makes it an anti-cancer factor; we just can't put reliable numbers on it yet.