Dairy milk may be a cause of breast cancer, new study finds

In a new study, researchers found that intake of dairy milk is linked to a greater risk of breast cancer in women.

They found that even relatively moderate amounts of dairy milk consumption can increase women’s risk of breast cancer—up to 80% depending on the amount consumed.

They say the findings provide fairly strong evidence that either dairy milk or some other factor closely related to drinking dairy milk is a cause of breast cancer in women.

The research was conducted by a team at Loma Linda University Health.

Current U.S. dietary guidelines recommend three cups of milk per day. But evidence from this study suggests that people should view that recommendation with caution.

Dietary intakes of nearly 53,000 North American women were evaluated for the study, all of whom were initially free of cancer and were followed for nearly eight years.

By the end of the study period, there were 1,057 new breast cancer cases during follow-up. No clear associations were found between soy products and breast cancer, independent of dairy.

But, when compared to low or no milk consumption, the team found higher intakes of dairy calories and dairy milk were linked to a greater risk of breast cancer, independent of soy intake.

Consuming as little as 1/4 to 1/3 cup of dairy milk per day was associated with an increased risk of breast cancer of 30%.

By drinking up to one cup per day, the associated risk went up to 50%, and for those drinking two to three cups per day, the risk increased further to 70% to 80%.

The results had minimal variation when comparing intake of full fat versus reduced or nonfat milk; there were no important associations noted with cheese and yogurt.

The team says dairy foods, especially milk, were linked to increased risk, and the data predicted a marked reduction in risk linked to substituting soy milk for dairy milk.

This raises the possibility that dairy-alternate milk may be an optimal choice.

The team says the possible reasons for these associations between breast cancer and dairy milk may be the sex hormone content of dairy milk, as the cows are of course lactating, and often about 75% of the dairy herd is pregnant.

Breast cancer in women is hormone-responsive cancer.

Further, intake of dairy and other animal proteins in some reports is also associated with higher blood levels of a hormone, insulin-like growth factor-1 (IGF-1), which is thought to promote certain cancers.

The lead author of the study is Gary E. Fraser, MBChB, Ph.D.

The study is published in the International Journal of Epidemiology.

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