Final cessation of menstruation , ending female fertility .
It usually begins between ages 45 and 55. A gradual decline in function of the estrogen production. Ovulation becomes irregular and gradually ceases. The length of the menstrual cycle and periods may vary; flow may lessen or increase. Adjustment of the endocrine system to estrogen reduction causes hot flashes, often at night, with a warm sensation, flushing, and sweating; other symptoms, such as irritability and headaches, may be related more to reactions to aging. Removal or destruction of the ovaries to treat disease causes artificial menopause, with similar but more sudden effects. Changes in hormone balance usually cause no physical or mental disturbances. However, the protective effect of estrogen against osteoporosis and atherosclerosis is lost, and risks of fracture and coronary heart disease increase.