A new study has found a link between beef consumption, obesity and breast cancer. The study was designed to investigate the impact of zeranol, an anabolic growth promoter used by the U.S. beef industry to stimulate cattle growth, on hormone receptor positive human breast cancer cells. In obesity, the production of leptin, a hormone secreted primarily by fat cells, is enhanced. Leptin has also been shown to promote breast cancer cell growth. The study compared the effects of leptin, zeranol, and a polyphenol with known anti-cancer activities, on the growth of human breast cancer cells. Leptin was found to enhance the sensitivity of breast cancer cells to zeranol; the combination increased cancer cell growth. The findings suggest that exposure to zeranol may lead to initiation of transformation of normal breast cells to breast precancerous cells. The authors conclude that obese individuals may be at greater risk of developing zeranol-induced breast cancer.

Previous studies have also reported beef-breast cancer connection

Numerous previous studies have also reported an association between beef consumption and increased risk of breast cancer, but not all studies have found this association. The risk appears to be higher for hormone receptor positive (ER+/PR+) breast cancer, suggesting that women who have already been diagnosed with this form of the disease should avoid beef consumption. The current study elucidates a new mechanism by which beef consumption may promote breast cancer in overweight women, namely, an interaction between the fat hormone leptin and zeranol (Ralgro) used to stimulate the growth of beef cattle in the U.S.

Other factors have also been proposed to account for the apparent association between beef consumption and increased breast cancer risk. These include (1) the consumption of carcinogenic heterocyclic aromatic amines when beef is cooked very well done; (2) irradiation of beef, which has been found to result in the formation of mutagenic compounds; (3) heme iron contributed to the diet by regularly consuming beef, which has been found to be associated with an increased risk of breast cancer; and (4) the presence of bovine leukemia virus (estimated to infect at least 14% of U.S. beef herds), which is thought by some observers to be capable of contributing to human breast cancer.