Obesity and oral contraceptives reduce the preventive benefit of breastfeeding against breast cancer in Mexican women

Breast Cancer (BC) is the leading cause of dead in women over 25 years in Mexico, there are reproductive risk factors associated with BC, these factors include obesity, menarche, number of pregnancies, age at the first childbirth, duration of breastfeeding, use of oral contraceptives (OC), menopause and hormonal therapy. Among risk factors, breastfeeding is particularly interest for BC prevention. Breastfeeding in Mexico has decreased dramatically in the last 20 years and obesity, and the use of OC have been on the rise. The objective of this study is to identify whether the protective factor of breastfeeding against breast cancer is affected by obesity and OC use. We conducted a case-control study in women aged 30-81 years from Oncology Service, UANL in Mexico. We included 336 BC cases, and 336 controls (matched by age). Information regarding of breastfeeding and reproductive factors was collected. Odd ratios and 95% confidence intervals (CI) were calculated using multiple logistic regressions, and a chi-square. We found that women who had at least one child, presented protective effect against BC (OR 0.034; 95% CI 0.008-0.140). The women who had taken a OC (OR 2.334; CI 95% 1.565-3.481) and whom who had obesity (OR 4.356; CI 95% 2.969-6.322) had higher risk of BC. BC cases that breastfeed more than 13 months were stratify by use of OC, we found an increased risk in patients that use OC vs non-OC consumers (p=0.004).OC consumers that breastfeed after 30 years has an increased risk compared with patients non-OC consumers (p=0.013). Obesity and OC decrease the protection effect of lactation on BC.