Dairy Milk Associated with Increased Risk of Breast Cancer

Depending on the amount consumed, intake of dairy milk can increase the risk of breast cancer by up to 80%, according to new research from Loma Linda University Health.¹

"Consuming as little as [one-quarter] to [one-third] cup of dairy milk per day was associated with an increased risk of breast cancer of 30%," said Gary E. Fraser, MBChB, PhD, first author of the paper, in a statement. "By drinking up to 1 cup per day, the associated risk went up to 50%, and for those drinking 2 to 3 cups per day, the risk increased further to 70% to 80%."²

Although current US dietary guidelines recommend 3 cups of milk per day,¹ Fraser noted that the results suggest alternative options, such as almond milk, may be better options.²

The study is part of the Adventist Health Study (AHS)-2, a long-term study investigating the links between lifestyle, diet, and disease among members of the Seventh-day Adventist Church.²

The researchers evaluated the dietary intakes of nearly 53,000 women, all of whom were initially cancer-free. The intake levels were estimated from food frequency questionnaires, and a baseline questionnaire established demographics, family histories of breast cancer, physical activity levels, alcohol consumption habits, hormonal and other medication use, breast cancer screenings, and reproductive and gynecological history.¹ The participants were followed for 8 years.¹

During follow-up, there were 1057 new breast cancer cases. Notably, no clear association was found between soy products and breast cancer independent of dairy. However, when compared with low or no milk consumption, higher intake of dairy calories and dairy milk were associated with a greater risk of breast cancer independent of soy intake.¹

These findings are consistent with the recent AHS-2 report, which suggested that vegans experienced less breast cancer than non-vegetarians, but vegetarians who consume eggs and dairy products did not experience the same results.¹

Although the possible reasons for this association are not confirmed, Fraser said it may have something to do with the sex hormone content of dairy milk.² Breast cancer in women is a hormone-responsive cancer. Furthermore, intake of dairy and other animal proteins in some reports has also been associated with higher blood levels of a hormone, insulin-like growth factor-1, which is believed to promote certain cancers.¹

“Dairy milk does have some positive nutritional qualities,” Fraser said in a statement. “But these need to be balanced against other possible, less helpful effects. This work suggests the need for further research.”²

REFERENCES

• Fraser G, Jaceldo-Siegl K, Orlich M, Mashchak A, et al. Dairy, soy, and risk of breast cancer: those confounded milks. International Journal of Epidemiology; February 25, 2020. https://academic.oup.com/ije/advance-article-abstract/doi/10.1093/ije/dyaa007/5743492?redirectedFrom=fulltext. Accessed February 28, 2020.
• New study associates intake of dairy milk with greater risk of breast cancer [news release]. Loma Linda, CA; February 25, 2020. https://news.llu.edu/research/new-study-associates-intake-of-dairy-milk-with-greater-risk-of-breast-cancer. Accessed February 28, 2020.