BRCA1 and obesity due to melanocortin 4 receptor deficiency: Therefore, we hypothesized that the rotating night work and such modifiable factors as cigarette smoking, alcohol drinking, physical activity, and obesity, may be associated with the methylation of the promoter regions within two tumor suppressor and DNA repair genes: BRCA1 and BRCA2. To examine this hypothesis, we investigated associations between the methylation status of the CpG island in the promoter of the BRCA1 and BRCA2 genes and the lifestyle factors, using data obtained from a cross-sectional study on nurses and midwives.