We mentioned a few pages back that men can have problems due to estrogen imbalances, so it stands to reason that estrogen and other hormones need to remain balanced in women as well. Of course, there's a wide range of normal depending on the person. The biggest culprit is estrogen; too little or too much can lead to serious health problems.
When estrogen levels get low, women lose bone density and have an increased risk of osteoporosis and bone fractures. They may also have a higher risk of heart disease due to raised cholesterol levels. While lowered estrogen is a normal part of menopause, some women experience imbalances due to premature ovarian failure (POF) -- menopause before the age of 40. Hormone replacement therapy (HRT) can help with this and other health issues associated with low estrogen, although in recent years HRT has gotten some criticism for other potential side effects, such as blood clots. On the other end of the spectrum, estrogen can also cause some forms of breast cancer to grow once established. This is known as a hormone-receptor-positive cancer, and patients may be prescribed anti-estrogen therapy.