Oestrogen and Progesterone

Oestrogen and progesterone are hormones produced in a woman’s ovaries before menopause. They play an important part in the menstrual cycle and pregnancy, but oestrogen also helps maintain bone strength and might prevent heart disease and protect memory before menopause.

For more than 60 years oestrogen has been used by millions of women to control the hot flashes and vaginal dryness that frequently occur with menopause. It is also used to prevent or treat osteoporosis, the loss of bone strength that often occurs after menopause. However, over time experts realized that oestrogen could cause a thickening of the lining of the uterus (endometrium) and an increased risk of endometrial cancer. Doctors then began giving progestin, a synthetic form of progesterone, to protect the lining of the uterus. Using oestrogen alone (in a woman whose uterus has been removed) or with a progestin (in women with a uterus) to treat the symptoms of menopause is called menopausal hormone therapy (MHT), formerly known as hormone replacement therapy.

Unlike other hormones described in this fact sheet, many large, reliable long-term studies of oestrogen and its effects on the body have been conducted. These studies suggested that using oestrogen after menopause could provide many important benefits.

But oestrogen also is a good example of why it is important to wait until researchers have discovered both the benefits and risks of a hormone before it becomes widely used. While some women are helped by oestrogen during and after menopause, others are placed at higher risk for certain diseases if they take it.

Early studies suggested menopausal hormone therapy could lower the risk for heart disease (the number-one killer of women in the United States) in postmenopausal women. But results from the Women’s Health Initiative (WHI), an important study of menopausal hormone therapy funded by the National Institutes of Health, now suggests that using oestrogen with or without a progestin after menopause does not protect postmenopausal women (ages 50 and older) from heart disease and may even increase their risk. In 2002, WHI scientists reported that using oestrogen plus progestin actually elevates some women’s chance of developing heart disease, stroke, blood clots, and breast cancer. But they also found health benefits—not as many hip fractures and fewer cases of colorectal cancer. In 2004, the same scientists reported that using oestrogen alone increased a woman’s risk of stroke and blood clots, but protected women from hip fractures.

Some studies suggest that oestrogen may protect against Alzheimer’s disease, but this has not yet been proven. In fact, in 2003, researchers in a WHI substudy, the WHI Memory Study (WHIMS) reported that women age 65 and older taking a combination of oestrogen plus progestin were at twice the risk of developing dementia as women not taking any hormones. Again in 2004, these WHIMS scientists reported that using oestrogen alone could increase the risk of developing dementia in women age 65 and older compared to women not taking any hormones.

As a result of these studies, experts have concluded that the health risks of using menopausal hormone therapy may be greater than the health benefits. These risks may differ between women who have menopausal symptoms and those who don’t. Nevertheless, the FDA has stated that women who want to use menopausal hormone therapy to control the symptoms of menopause should do so at the lowest effective dose for the shortest time needed.

But the question of these greater risks is still an important public health issue. Even small increases, when millions of women are using menopausal hormone therapy, could mean many more cases of heart disease, stroke, blood clots, and breast cancer.

So the decision whether to take oestrogen is now far more complex and difficult than ever before. Questions about menopausal hormone therapy remain: Would using a different oestrogen and/or progestin or another dose change the risks? Would the results be different if the hormones were given as a patch or cream, rather than a pill? Would taking the progestin less often be as effective and safe? Does starting menopausal hormone therapy around the time of menopause compared to beginning years later change the risks? Can we predict which women will benefit or be harmed by using menopausal hormone therapy? As answers to these and other questions are found, women and their doctors should frequently review the pros and cons of menopausal hormone therapy in order to make an informed choice based on a realistic assessment of personal risks and benefits.