Evidence Mounts For Protective Effect Of Vitamin D And Calcium

Main Category: Cancer / Oncology
Also Included In: Women's Health / Gynecology
Article Date: 07 Aug 2007 - 1:00 PST

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Postmenopausal women who take supplements of calcium and vitamin D may have a reduced risk of developing cancer, according to the results of a randomised controlled trial published in the American Journal of Clinical Nutrition.

Although there is good evidence to suggest that exposure to sunlight is inversely related to cancer incidence, data supporting a link between vitamin D and cancer is derived largely from observational studies. To add trial data to this evidence base, researchers from Creighton University, Omaha, USA, enrolled 1179 women who were older than 55 years and had no history of cancer and randomly assigned them to supplements of calcium alone, calcium plus vitamin D, or placebo for 4 years. The primary outcome was fracture incidence, the results of which will be presented in another paper, and the principal secondary outcome was cancer incidence.

The researchers found that women who received both calcium (1400-1500 mg/day) and vitamin D (1100 IU vitamin D3/day) supplements had a lower incidence of cancer than women who received placebo (13 cases among 446 women compared with 20 cases among 288 women). 17 of the 445 women who took calcium alone developed cancer during the 4 year period.

When the researchers repeated the survival analysis for those women who were free of cancer at 1 year---on the basis that cancers diagnosed early in the study would have been present, although unrecognised, on entry---the total number of incident cancers fell to 37 and the relative risk for the calcium and vitamin D group fell from 0.402 to 0.232, compared with placebo.

"Our findings of decreased all-cancer risk with improved vitamin D status are consistent with a large and still growing body of epidemiologic and observational data showing that cancer risk, cancer mortality, or both are inversely associated with solar exposure, vitamin D status, or both," write the authors. "These findings highlight the importance of promoting optimum vitamin D status and underscore the value of achieving and maintaining a high serum 25(OH)D concentration."

In a separate study published in the Archives of Internal Medicine, researchers from Brigham and Women's Hospital and Harvard Medical School, USA, looked at the relation between total intakes of calcium and vitamin D from dietary and supplemental sources and breast cancer risk among women from a large cohort study.

They studied 31 487 women, 34% of whom were premenopausal, who took part in a randomised controlled trial evaluating low-dose aspirin and vitamin E therapy for the primary prevention of cancer and cardiovascular disease. The women were 45 years or older and were free of cancer and cardiovascular disease when they were enrolled in 1993 and 1995. As part of the trial, the women completed a self-administered questionnaire at baseline about their medical history and lifestyle factors, which included a 131-item food frequency questionnaire. Based on the results of the questionnaire, the researchers calculated what the participants' total intake of calcium and vitamin D was likely to be.

During an average of 10 years of follow-up, 276 premenopausal and 743 postmenopausal women had a confirmed diagnosis of incident invasive breast cancer. The researchers found that higher intakes of total calcium and vitamin D were moderately associated with a lower risk of premenopausal breast cancer. By contrast, intakes of both nutrients were not associated with the risk of breast cancer among postmenopausal women.

"Findings from this study suggest that higher intakes of calcium and vitamin D may be associated with a lower risk of developing premenopausal breast cancer. The likely apparent protection in premenopausal women may be more pronounced for more aggressive breast tumours," write the authors.

-- Vitamin D and calcium supplementation reduces cancer risk: results of a randomized trial
Lappe JM, Travers-Gustafson D, Davies KM, Recker RR, Heaney RP.
American Journal of Clinical Nutrition 2007;85:1586-91.

-- Intakes of calcium and vitamin D and breast cancer risk in women
J Lin, JE Manson, IM Lee, NR Cook, JE Buring, SM Zhang.
Archives of Internal Medicine 2007;167:1050-59.

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