Dairy consumption and calcium intake and risk of breast cancer in a prospective cohort: The Norwegian Women and Cancer study

To study the association between consumption of dairy products and calcium intake and risk of breast cancer risk according to menopausal status. In a population-based prospective cohort study of 64,904 Norwegian women followed from 1996/1999 through 2006, we examined total dairy consumption and consumption of various dairy products in relation to pre- and postmenopausal breast cancer risk. We also examined breast cancer in relation to calcium intake and to milk consumption during childhood and performed additional analyses corrected for measurement errors in the dietary data. In total, 218 premenopausal and 1,189 postmenopausal incident breast cancer cases were diagnosed during follow-up. Total dairy, adult, and childhood milk consumption was not associated with either pre- or postmenopausal breast cancer risk. Premenopausal women with the highest consumption of white cheese had half the risk of breast cancer compared to those with the lowest consumption (hazard rate ratio in the 4th quartile vs. the 1st quartile 0.50, 95% confidence interval 0.29-0.87). Total calcium intake tended to be inversely related to premenopausal (hazard rate ratio in the 4th quartile vs. the 1st quartile 0.65, 95% confidence interval 0.39-1.08) and postmenopausal breast cancer (hazard rate ratio in the 4th quartile vs. the 1st quartile 0.85, 95% confidence interval 0.70-1.04). Correcting for measurement errors did not alter the results substantially, nor did exclusion of early cancer cases. Dairy consumption is not strongly related to breast cancer risk in this prospective study. A non-significant negative association between calcium intake and breast cancer risk was seen, particularly among premenopausal women.