Summarized by Robert W. Griffith, MD
In a prospective randomized study, calcium-plus-vitamin D capsules significantly reduced the risk of cancers of different types in postmenopausal women.
It’s been known for more than 50 years that exposure to the sun’s rays protects against some cancers – breast, rectum, ovary, prostate, stomach, bladder, esophagus, kidney, lung, pancreas, and uterus, as well as non-Hodgkin lymphoma and multiple myeloma. Researchers first proposed that vitamin D was responsible 25 years ago. Since then, associations have been found between colorectal and prostate cancer and low blood levels of vitamin D. All these findings are based on what are called “observational studies”. Now a double-blind, placebo-controlled trial of calcium and vitamin D supplementation has been done, in which the occurrence of cancer was an important outcome. Its findings have been published in the American Journal of Clinical Nutrition, and are summarized below.
What was done
Rural areas in eastern Nebraska, USA, supplied the participants for this study, who were women recruited by random telephone dialing. They had to be over 55, have no known cancers, and be healthy. The prime purpose of the study was to establish the benefits of supplemental vitamin D and calcium on the incidence of bone fractures, but the secondary focus was on the occurrence of cancer.
The subjects were randomly assigned to one of three treatments: placebo (vitamin D placebo and calcium placebo), calcium (either calcium citrate 1400 mg/day or calcium carbonate 1500 mg/day, plus vitamin D placebo), or calcium (as above) plus vitamin D (1100 IU cholecalciferol).
Out of 1180 women enrolled, just over 1000 completed the 4-year study. Serum samples taken at baseline and then annually measured 25(OH)D (25-hydroxy-vitamin D). Health status was assessed every 6 months.
What was found
Fifty women developed a non-skin cancer during the 4 years of the study. For all cancers combined, both the calcium-alone and the calcium-plus-vitamin D groups had rates less than those taking just the placebo; the likelihoods of developing cancer were 40% (calcium) and 53% (calcium-plus-vitamin D) of the rate for the placebo group, respectively.
The analysis was repeated for the occurrence of cancer between years 1 and 4 (the theory being that cancers diagnosed early in the study would have been present, though unrecognized, on enrollment). The likelihoods of developing cancer were 59% (calcium) and 23% (calcium-plus-vitamin D) of the rate for the placebo group, respectively.
The specific cancers that all showed a reduced incidence with calcium-plus-vitamin D over the 4 year period were cancer of the breast, colon, and lung, and lymphoma, leukemia, and myeloma.
The serum 25(OH)D levels were significant independent predictors of cancer risk. Calculations showed a 35% reduction in cancer risk for every 10 ng/mL increase in serum 25(OH)D levels.
What these findings mean
This study showed a decreased all-cancer risk with vitamin D supplementation, i.e. sufficient additional vitamin D to raise serum 25(OH)D levels more than 10 ng/mL – about 1000 IU of cholecalciferol. The findings are consistent with data from studies demonstrating roles for solar exposure, vitamin D status, or both.
The results for the calcium-only supplementation were marginal, and may have been a chance occurrence, according to the authors of the study. It’s known that calcium supplementation can reduce the number of colon polyps and prostate cancer; however, in this study only 3 of the 50 cancers were colon cancer.
This study was confined to women, because of the planned primary outcome, osteoporotic fractures. But it’s reasonable to assume that the findings would apply to men, as well.
The link between too much sun and skin cancer is well established. But the benefit of sunshine in promoting synthesis of vitamin D should not be overlooked; indeed, some scientists recommend that 15 minutes in the sun twice a week should be sufficient to ward off vitamin D deficiency. Just don’t overdo it.
Vitamin D and calcium supplementation reduces cancer risk: results of a randomized trial. JM. Lappe, D. Travers-Gustafson, M. Davies, et al., Am J Clin Nutr, 2007, vol. 85, pp. 1586–1591