In a population-based study, 1180 Caucasian women older than 55, were randomized to receive a calcium supplement , a calcium supplement plus 1100 IU of vitamin D (cholecalciferol), or a daily placebo. Health status and compliance to the regimen were assessed every 6 months over 4 years and serum vitamin D was measured at baseline and annually. 1024 women completed the study. The purpose of the analysis was to determine the efficacy of calcium by itself and calcium plus vitamin D in reducing the all-cancer risk in postmenopausal women.
Fifty women developed cancers other than skin cancer. The risk for cancer in the calcium-plus vitamin-D group was less than half that in the placebo group (RR 0.4; P=0.013). The calcium only group had no statistically significant risk reduction. Researchers adjusted for the possibility that cancers detected during the first year of the study, had been present but silent at baseline, and analyzed these separately. Relative risk for cancer in the calcium/vitamin D group was lower than in the placebo control subjects 0.2 (P< 0.005), and the risk reduction for the calcium only group was not statistically significant.
Women in the calcium plus vitamin D group had higher serum vitamin D levels that correlated with lower cancer risk, both at baseline and at one year. Adherence to the study doses was 86%.
Lappe JM, et al. Vitamin D and calcium supplementation reduces cancer risk: Results of a randomized trial. Am J Clin Nut 2007; Jun;85(6):1586-1591
Commentary: The only other randomized trial of vitamin D and cancer was the Women’s Health Initiative, which used a lower dose of vitamin D (400 IU) and women with a lower baseline vitamin D status. The WHI reported no significant effect of the vitamin D intervention on colorectal cancer incidence but did observe a significant inverse relation between baseline vitamin D levels and cancer risk, as in this study. It’s reassuring to see that the benefits of higher than recommended dosing of vitamin D is catching on. It is estimated that about 60% of women in the U.S. are vitamin D deficient, no what part of the country they live in. The current adult daily recommendations for vitamin D in women 51 to 70 is
400 IU -800 IU per day. Supplement doses up to 2000 IU are considered safe and to be without significant risk for adverse events. Many practitioners are advising even higher doses, but I would recommend this only after assessment for medical need, serum testing, and evaluation for risk of side effects.
Calcium and Vitamin D Intake and Risk for Breast Cancer
The relationship between vitamin D and breast cancer was prospectively assessed among 10,000 premenopausal and 20,000 postmenopausal women who were enrolled in the Women’s Health Study. Intake of calcium and vitamin D was determined from self-reported questionnaires about diet and vitamin use.
During an average follow-up of 10 years, the overall incidence of invasive breast cancer was 2.6% among premenopausal women and 3.6% among postmenopausal women. Among premenopausal women, the hazard ratio for developing breast cancer was 0.61 for women in the highest versus lowest quintiles of calcium use and 0.65 for vitamin D intake. No benefit was seen for these nutrient intakes and breast cancer risk in postmenopausal women.
Lin J et al. Intakes of calcium and vitamin D and breast cancer risk in women. Arch Intern Med 2007, May 28; 167(10):1050-1059.
Commentary: This is a very large, prospective study, which once again demonstrates important findings for vitamin D, at least for premenopausal women. A higher intake of calcium and vitamin D was associated with a lower risk for breast cancer among premenopausal women, but not for postmenopausal women. While the hazard ratio was large, the absolute reduction in risk was small. Being a population based study using only self-reported questionnaires, the usefulness of the findings in this study are limited, especially since the amount of vitamin D and calcium was recorded only once at baseline. In addition, there could easily be other variables that explain the findings. Nonetheless, it supports the trend to advise women about adequate intakes of calcium and vitamin D, both in the diet and in supplement form.
