Does eating meat increase risk for breast cancer?
Consumption of red and processed meat has been linked with colorectal, pancreatic and prostate cancer, but its association with breast cancer has been unclear due to conflicting findings from previous studies. A recent meta-analysis, published in the International Journal of Cancer, takes a closer look at the evidence regarding red meat and breast cancer.
For the analysis, the authors identified 466 relevant citations published up until January, 2018. Red meat was defined as unprocessed muscle meat including beef, veal, pork, lamb, mutton, horse, or goat meat. Processed meat refers to meat that has been transformed through salting, curing, fermentation, smoking or other processes to enhance flavor or improve preservation.
After screening, the authors whittled the studies down to 20 published articles on red meat, processed meat, or total red meat (red meat and processed meat) and breast cancer incidence. They included cohort studies, nested case-control studies, and clinical trials. Eight studies were from North America, nine studies were from North America, and one study was from Japan. For all but two studies, which used dietary records, diet was assessed through a food frequency questionnaire. The amount of meat consumed was recorded as gram/day or week, serving/day, or gram/1000 kcal.
The authors conducted three separate analyses for red meat, processed meat and total red meat. A total of 1,1 million women and 33,493 cases of breast cancer (13 studies), were included in the red meat and overall breast cancer meta-analysis. A total of 1.25 million women and 37,070 cases of breast cancer were included in 15 studies of processed meat as were more than a half million women and more than 21,000 cases of breast cancer in the seven studies of total red meat.
Across 13 studies that examined the association between red meat and overall breast cancer, red meat consumption was associated with a nonsignificant increased risk of breast cancer. The random-effects summary of relative risks (RR) comparing the highest vs. the lowest category of red meat was 1.06 (95% CI: 0.99, 1.14) with moderate inconsistency across the studies. Among 15 studies that examined the association between processed meat and overall breast cancer risk, the risk estimate comparing the highest vs. the lowest category was 1.09 (95% CI: 1.03, 1.16). Among seven studies that examined the association between total red meat and overall breast cancer, the risk estimate comparing the highest vs the lowest category was 1.09 (95% CI: 0.99, 1.21).
The authors also examined the association between red and processed meat and risk of premenopausal and postmenopausal breast cancer. Among six cohort studies examining red meat intake and premenopausal breast cancer, the risk estimate comparing the highest vs the lowest category was 1.07 (95% CI: 0.97, 1.18). Among nine studies that examined the association between red meat intake and postmenopausal breast cancer, the risk estimate comparing the highest vs the lowest category was 1.08 (95% CI: 0.99, 1.17). A higher intake of processed meat was not associated with an increased risk of premenopausal breast cancer, but it was associated with a higher risk of postmenopausal breast cancer (highest vs lowest category RR = 1.10, 95% CI: 1.03, 1.17).
The authors said their study had several strengths and limitations. Identified strengths include limiting their analysis to prospective cohort, nested case-control, and clinical trials. The included studies also had wide variations in study populations, but low to moderate heterogeneity across the studies themselves allowed the authors to feasibly pool the results from the different studies. The authors also had the ability to evaluate the association of red meat intake and breast cancer events in different populations with different diets. Identified limitations included publication bias, the possibility of residual confounding, and the fact that some of the included studies also included processed poultry in their definition of processed meat. However, the authors believe that their findings illustrate a significant risk of breast cancer with the intake of processed meat and physicians should counsel their patients about it and suggest diet changes as a preventative measure.