One cup of milk per day associated with up to 50 per cent increase in breast cancer risk: study
TORONTO -- New evidence suggests that women who drink as little as one cup of dairy milk per day could increase their risk of developing breast cancer by up to 50 per cent.
Researchers from the Loma Linda University Adventist Health Sciences Center in California say the observational study gives "fairly strong evidence" that dairy milk or factors closely related to the consumption of dairy milk is linked to the development of breast cancer in women.
"Consuming as little as one-quarter to one-third of a cup of dairy milk per day was associated with an increased risk of breast cancer of 30 per cent," study author Dr. Gary Fraser said in a press release.
"By drinking up to one cup per day, the associated risk went up to 50 per cent, and for those drinking two to three cups per day, the risk increased further to 70 per cent to 80 per cent."
More alarmingly, Fraser points out that these figures correspond with the current U.S. dietary guidelines, which recommend three cups of milk per day for adults.
"Evidence from this study suggests that people should view that recommendation with caution," Fraser said.
For the study, which was conducted as part of the Adventist Health Study-2, a long-term health study examining the lifestyle of members of the Seventh-Day Adventist Church, researchers followed the dairy consumption of nearly 53,000 women across North America from 2002 to 2007.
The female participants were recruited from Adventist churches throughout the U.S., except for Maine, and in Ontario, Alberta, and British Columbia. The women were aged 30 years and older with a mean age of 57. Participants’ family history of breast cancer, physical activity, alcohol consumption, medication use, and reproductive and gynecological history were also taken into consideration.
By the end of the study, 1,057 new breast cancer cases had been diagnosed.
Although no clear associations were found between soy products and breast cancer, those who had higher intakes of dairy milk were at greater risk of developing breast cancer when compared to those who drank little to no milk.
"The data predicted a marked reduction in risk associated with substituting soymilk for dairy milk. This raises the possibility that dairy-alternate milks may be an optimal choice,” said Fraser.
Researchers noted that the consumption of full fat versus reduced or nonfat milks had little impact on the results.
The study notes that the association between breast cancer and dairy milk could be related to the sex hormone content of the milk, noting that often 75 per cent of the dairy herd is pregnant.
Researchers also note that intake of dairy and other animal proteins has previously been associated with higher blood levels of the growth factor-1 (IGF-1) hormone, which is thought to promote certain cancers.
In a statement to CTVNews.ca, Dairy Farmers of Canada expressed concern over the study, noting that the findings could be misleading.
“The authors themselves note a number of limitations of the study,” a spokesperson said, noting that the study was observational and did not control other risk factors in participants, making it hard to draw specific conclusions.
The study also notes that “causality specifically attributable to dairy products is not proven by this work.”
Dairy Farmers of Canada also points towards research from the World Cancer Research Fund, noting “evidence suggests that total dairy product consumption is either not associated with risk of breast cancer or may reduce the risk of breast cancer. Milk is specifically not associated with risk in both pre and post-menopausal women.”
A spokesperson noted that previous studies linking the association between dairy consumption and breast cancer in women have produced conflicting results.
Study authors note that although dairy milk does have “some positive nutritional qualities," additional research is required to understand the link between dairy consumption and certain cancers.
In January, Canada's Food Guide was updated for the first time in more than a decade and noticeably de-emphasized dairy consumption, suggesting instead that water should be Canadians’ "beverage of choice."
Lower-fat milk and plant-based beverages are listed as other options, though less preferred.
The study was funded by the National Cancer Institute at the National Institutes of Health in the U.S.