The hormonal transitions in a woman's life are like a long rollercoaster ride. During adolescence, your ovaries respond to signals from your brain and begin producing the hormones estrogen, progesterone, and testosterone. Soon after, monthly ovulation begins, followed by your menstrual periods if the eggs you produce are not fertilized.
For about 25 years, from ages 13–40, you are most fertile. After that, for 10 to 15 years, there's a gradual decline in ovarian function and the amount of hormones you produce. This time of declining ovarian function is called the climacteric.
Eventually, the amount of estrogen and progesterone your ovaries produce is no longer enough to bring on ovulation and keep your monthly periods going. The result: your periods become irregular; you may experience hot flashes; you may feel moody, less than happy. This 1- to 3-year period of hormonal flux before your periods stop completely is called perimenopause. When your periods finally stop completely (for at least a year) is you are officially in menopause.
How mild or severe your menopausal symptoms are depends on how fast you move from perimenopause to menopause, how much time your body has to adapt to its changing hormones, and how much estrogen your body has from other sources. After menopause, most of your estrogen comes from androgens manufactured by the adrenal glands above your kidneys. Your fat and muscle cells convert the androgens to estrogens. The more fat and muscle that you have, the higher the level of estrogen produced by sources other than your ovaries. The most common symptom during a relatively quick move from perimenopause to menopause is hot flashes.
You might go through natural menopause and very mild side effects because the transition is long, smooth, and gentle. Perhaps you have an excess of fat, muscle, or both that is making an alternate supply of estrogen. But a fair number of you reading this section have experienced a more abrupt move into menopause because of breast cancer diagnosis and treatment.