Steven Narod from the University of Toronto, Canada, and colleagues from universities in Canada, the USA and Poland studied two groups of women, all of whom had a mutation in one of the breast cancer susceptibility genes BRCA1 and BRCA2. The first group had been diagnosed with breast cancer while the second group had not. Each member of the first group was paired up, or 'matched', with a woman from the second group who was the same age, carried a mutation in the same gene and lived in the same country. This is the largest study of this kind to date, with 1073 women from five different countries in each group. By comparing the two groups, the researchers could identify the relationship between the incidence of breast cancer before the menopause in women at risk, and weight at 18, 30 and 40 years of age.
Their results show that, for women who have a mutation in BRCA1, "weight loss of at least 10 pounds was associated with a 65% reduction in cancer risk between ages 30 and 40." The study also shows that BRCA1 mutation carriers who gained 10 pounds or more between 18 and 30 years of age are 44% more at risk of developing breast cancer if they have 2 children or more. No association between weight loss and breast cancer risk was shown in BRCA2 mutation carriers.
Changes in Body Weight and the Risk of Breast Cancer in BRCA1 and BRCA2 Mutation Carriers
Joanne Kotsopoulos, Olufunmilayo I. Olopado, Parviz Ghadirian, Jan Lubinski, Henry T. Lynch, Claudine Isaacs, Barbara Weber, Charmaine Kim-Sing, Peter Ainsworth, William D. Foulkes, Andrea Eisen, Ping Sun, Steven A. Narod
Breast Cancer Research 2005, 7:R833-R843