Association between soy, dairy intakes and breast cancer risk has been inconsistent. Thus far, there have been no comprehensive studies to assess this fact conclusively. However, a new study, from Loma Linda University’s Adventist Health Sciences Center, has found that intake of dairy milk is associated with a greater risk of breast cancer in women.
The study, published in the International Journal of Epidemiology, evaluated the potential breast cancer risk associated drinking dairy milk and soy milk. Depending on how much milk is consumed, dairy was found to increase the risk of breast cancer by up to a massive 80%.
These astounding findings conflict with the present US dietary guidelines which advise people to drink three cups of milk daily. In complete contradiction, the study has found that as little as 1/4 or 1/3 cup of daily cow milk can increase breast cancer risk by 30%.
For the study, data from more than 52,000 women located in North America was analysed. None of the women at the time of the study's start was diagnosed with breast cancer. Over the course of nearly eight years, the participating women were tracked; 1,057 cases of breast cancer were reported among them.
No clear associations were found between soy products and breast cancer, independent of dairy. But, when compared to low or no milk consumption, higher intakes of dairy calories and dairy milk were associated with greater risk of breast cancer, independent of soy intake. The researchers have also noted that the results had minimal variation when comparing intake of full-fat versus reduced- or non-fat milk. There were also no important associations noted with cheese and yogurt.
Dr Gary E Fraser, lead author of the study, believes that the current guidelines of dairy milk consumption should be viewed with some caution. “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%,” he explained.
Dr Fraser further said, “Dairy food, especially milk, were (sic) associated with increased risk and the data predicted a marked reduction in risk associated with substituting soy milk for dairy milk. This raises the possibility that dairy alternate (to) milks may be an optimal choice.”
Researchers believe that 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 lactating and, often, about 75% of the dairy herd is pregnant. Breast cancer in women is a 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 research team believes that the conclusions drawn from this study are vital and further comprehensive research is required. “Dairy milk does have some positive nutritional qualities, but these need to be balanced against other possible, less helpful effects. This work suggests the urgent need for further research,” said Dr Fraser.
