Young women's chances of breast cancer are suggested to increase with more red meat intake. Researchers conducted a study with 88,000 women and found a 20% increased risk of obtaining the disease, though a biological cause was not established.
The Harvard study asked women ages 26 to 45 to self-report their food intake from previous years, starting from when they were teenagers. For 20 years the researchers followed the women. 2,830 women in the study developed breast cancer, and there was a significant association between higher red meat in the diet and higher risk of developing the disease. The study also found, however, that increased poultry intake was associated with a decreased risk of developing breast cancer.
Based on the study, which was published in the BMJ on June 10, 1.5 daily servings of red meat could increase the risk of breast cancer by 22%, with each additional serving adding a 13% increase in risk. These statistics present a correlation rather than causation, and while the biological mechanisms are not understood, scientists present theories.
There is evidence that cooking red meat at high temperatures may cause carcinogens to be released, and giving hormone supplements to livestock may increase a person's hormone levels, which is linked to cancer. High-protein diets have also been associated with higher risks of cancer, but, according to the Harvard study, protein intake isn't the problem. Since researchers found a decreased risk of breast cancer in those that consumed poultry instead of red meat, as well as other sources of protein such as nuts, fish and legumes, it seems there is an alternative protein diet for fans of red meat.
Another study analyzed the number of moles on a woman's skin and found an association between this number and the risk of developing breast cancer. As per researcher Jiali Han, moles have never before been linked to breast cancer, only to melanoma. Han followed 75,000 women and asked them to self-report the number of moles on their left arm, taking into account already proven risk factors for breast cancer. Han and his fellow researchers found a 35% increased risk of breast cancer in women with 15 or more moles. Another study in France, published in PLOS medicine along with Han's research, found a 13% increase in the risk of developing breast cancer in women with "very many" moles.
The studies mentioned present many variables, such as onset of menopause in the subjects, which may affect the results of the study. The theory behind the link between moles and breast cancer is primarily based on evidence correlating the number of moles to sex hormone levels (estrogen and testosterone). However, further researcher is necessary before conclusions are drawn, according to Han.