An 8-year study has found that drinking cow’s milk greatly increases the risk of developing breast cancer in women- up to a staggering 80%.

Published in the International Journal of Epidemiology, the observational study conducted by researchers at the Loma Linda University in California examined 53,000 women over eight years and found that the risk of developing breast cancer in the ones drinking just a third of a cup was 30 per cent,  a full cup a day it led to 50 percent increase and 2 cups increased the risk to up to 80%.

Lead author Gary Fraser, professor of cardiology and nutrition at Loma Linda said the study showed a “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.

“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 study’s findings come at a time when the NHS promotes cow’s milk as a healthy source of protein and calcium, and the current U.S. Dietary guidelines recommend three cups of milk per day.

However, Fraser said: “Evidence from this study suggests that people should view that recommendation with caution.”

Study

Researchers evaluated diets for nearly 53,000 North American women, all of who were free of cancer initially.

The group was followed for eight years and was made to record their dietary habits through food frequency questionnaires (FFQ) and 24-hour recalls.

The participants also answered questions about demographics, family history of breast cancer, physical activity, alcohol consumption, hormonal and other medication use, breast cancer screening, and reproductive and gynecological history.

By the end of the study and during follow-ups, 1,057 participants from the group developed breast cancer.

Increased sex hormone levels in milk

While the researchers found a strong association between the cancer and milk consumption irrespective of whether it was full fat, reduced or non-fat milks, they could not ascertain a clear link between breast cancer and dairy alternatives such as soy products.

Based on the findings, Fraser said: “Dairy foods, especially milk, were 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 milks may be an optimal choice.”

Breast cancer is a hormone-responsive cancer and scientists believe the most probable reasons for dairy being linked to cancer risk in women is the level of sex hormone present in dairy milk.

Studies have shown that dairy milk contains high levels of Insulin-like growth factor (IGF-1) because cows are lactating when their milk is extracted and often about 75% of the dairy herd is pregnant and the resulting higher blood levels of this hormone is believed to promote certain cancers.

Fraser concluded stating: “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.”

Other studies

While the present study could not ascertain any important associations with cheese and yogurt, a separate study on cancer survivors indicated that those who consumed one or more servings of high-fat dairy products (e.g., cheese, ice cream, whole milk) increased their risk by 49 percent, as compared to those consuming less than one-half serving daily.

Another 2017 study funded by the National Cancer Institute showed that those who consumed higher amounts of American, cheddar, and cream cheeses had a 53 percent increased risk for breast cancer.

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