Why is age at menarche a risk factor for breast cancer?
Breast cancer is a disease that is thought to be related to high lifetime exposure to the hormone estrogen. Estrogen is needed for normal reproductive development and estrogen levels in the body rise at menarche. The earlier a girl starts menstruating, the more menstrual cycles she will have, and the greater will be her exposure to estrogen during her child-bearing years. Height, weight, diet, exercise, and family history have all been found to influence age at menarche. How do height, weight and body fat distribution affect the age at menarche? There is a trend towards an earlier age at menarche among girls living in industrialized countries. Taller, heavier girls generally start menstruating earlier than shorter, lighter girls. In addition, the distribution of fat on a girl’s body is related to the levels of hormones circulating in her body and may affect her age at menarche. Girls with fat localized around their hips (pear shaped), may have an earlier menarche than girls with abdomi
