The role of dairy products in the development of breast cancer has been a controversial topic for many years, with many experts suggesting a link between increased dairy consumption and rates of breast cancer. Recently, findings from the Adventist Health Study-2 appeared to support a link between cow milk and breast cancer. This observational study evaluated long-term impact of diet on health among a cohort of 52,795 Seventh Day Adventists.
A total of 1057 women developed invasive breast cancer over the course of 7.9 years of follow-up, with consumption of cow’s milk significantly associated with risk of breast cancer. Those women who consumed the highest number of calories from dairy per day had a 22% increase in risk for breast cancer compared to those who consumed the fewest calories from dairy (HR 1.22, P = .008). However, further analysis showed that the risk of breast cancer was increased significantly among postmenopausal women only, and not among premenopausal women.
Risk of breast cancer varied by type of dairy consumed, with cow’s milk consumption associated with a significant increase in risk of breast cancer, while consumption of cheese and yogurt having no associated increase in risk of breast cancer. Women who drank the most cow’s milk had a 50% increase in risk of breast cancer compared to those who drank the least cow’s milk (HR 1.5, P<.001). Importantly, the study also evaluated the link between soy intake and breast cancer rates and found no significant association. Indeed, when soy milk was substituted for cow’s milk, there was a 32% drop in risk of breast cancer among postmenopausal women (HR 0.68, P = .002).
The investigators concluded that these data support a link between consumption of cow’s milk and increased rates of breast cancer, particularly among postmenopausal women. These results appear to support other studies identifying a link between dairy and breast cancer. However, there is a need for prospective trial data to confirm the results seen in this observational study.
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