A cross-sectional study from the United Kingdom (the Breakthrough Generations Study) found that self-described vegetarians were more likely to have an earlier age of natural menopause. In turn, a lower age of menopause has been associated with lower rates of breast cancer.

The authors wrote:

“Vegetarians reached menopause at a mean age of 50.1 years, which was significantly earlier than non-vegetarians (mean menopausal age = 50.7 years, HR = 1.12; P < 0.001). The effect was present regardless of whether the woman became vegetarian before 20 years of age or between the ages of 20 and 40 years (data not shown)." This confirms previous reports that vegetarians have a lower age of menopause. Reference

Morris DH, Jones ME, Schoemaker MJ, McFadden E, Ashworth A, Swerdlow AJ. Body mass index, exercise, and other lifestyle factors in relation to age at natural menopause: analyses from the breakthrough generations study. Am J Epidemiol. 2012 May 15;175(10):998-1005. | link