http://www.niapublications.org/agepages/menopause.asp
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National Institute on Aging Information Center
Menopause is a normal part of life. It is one step in a long, slow process of reproductive aging. For most women this process begins silently somewhere around age 40 when periods may start to be less regular. Declining levels of the hormones estrogen and progesterone cause changes in your periods. These hormones are important for keeping the vagina and uterus healthy as well as for normal menstrual cycles and for successful pregnancy. Estrogen also helps to keep bones healthy. It helps women keep good cholesterol levels in their blood.