Drinking Milk, or Some Related Factor?
Fraser, the lead author of the current study, said in a statement that the results 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.”
That ‘other’ factor is probably complicated, but may be related to what humans have done to cows. To increase milk production, humans have bred cows to have higher levels of insulin-like growth factor, which in turn has been linked to some cancers, including breast cancer.
Sex hormones in cow’s milk may also be involved. About 75% of a dairy herd is pregnant and the cows are by definition lactating. So the milk they produce may have higher levels of progestins and estrogens, which may play a role in hormone-responsive breast cancer.
Other factors that researchers did not measure in this study, such as poverty and the income of participants, may be at play.
But to know what’s really going on, all agree that more research is needed.
“The overall evidence so far has not shown a clear increase or decrease in risk of breast cancer with higher [cow’s] milk intake. Thus, this topic needs further examination,” Willett said.
The study was funded by the National Cancer Institute at the National Institutes of Health, and the World Cancer Research Fund in the UK. Three of the authors report following largely vegetarian diets. All authors report regular and free use of dairy products without religious or other restrictions. No authors report associations with the soy product or dairy industries. Willett reports being a consultant during the design and early years of the Adventist study, but has not been involved with it for at least 8 years. Dizon has disclosed no relevant financial relationships.
This article first appeared on Medscape.com.