Estrogen is the hormone that regulates sexual and reproductive development in women, including the changes that occur during puberty. At menopause, a women’s estrogen production declines dramatically, resulting in symptoms such as hot flashes and insomnia.

But other changes occur with falling estrogen as well. As the amount of female estrogen goes down, a woman’s cholesterol level shifts, with harmful LDL cholesterol going up, while the “good” HDL cholesterol declines. Muscle mass also declines and bones can become brittle because estrogen plays a key role in bone growth.

When a women goes into premature menopause due to surgical removal of the ovaries, replacement hormones are prescribed. But during menopause, estrogen levels decline gradually, and whether they should be replaced has been a controversial topic for decades.

There are two types of hormones included in hormone replacement therapy. When estrogen alone is given, the therapy is known as estrogen therapy. When a progesterone component is also included, it is referred to as hormone therapy.