Montgomery Medicine No. 761

Hot Flashes

Sometimes I get asked questions in unusual places. A few months ago I was pulled aside at a store and asked if I could write about hot flashes.

Women typically describe hot flashes as a feeling of intense heat, usually with sweating and a rapid heartbeat. They can last a few minutes up to a half hour or so. The feeling usually starts on the face or upper chest but can also be on the neck and even spread over the entire body. Many women experience flushing of the skin over the involved area, hence their alternate name of hot flushes.

There is no hard and fast rule when, or if, a woman will develop hot flashes. Some women never have them, some are fortunate enough to have them for only a few months, while up to 45 percent may suffer for up to five to ten years. Some may have infrequent episodes while others may have them numerous times a day.

Hot flashes are caused by a reduced level of estrogen, the hormone that is made primarily by a woman’s ovaries. The production of estrogen gradually tapers off as a woman ages. If a woman has undergone surgical removal of the ovaries, the estrogen level drops rapidly and she develops “surgical menopause.”

One of estrogen’s biochemical targets in the body is the hypothalamus, a collection of nerve cells found at the base of the brain. One of the jobs of the hypothalamus is to regulate body temperature via the autonomic nervous system. Autonomic nerves cause blood vessels in the skin to either expand (vasodilation) causing a release of heat from the body, or to constrict (vasoconstriction) which helps the body conserve heat.

Blood levels of estrogen are in constant flux in and around menopause. This gives the hypothalamus confusing signals, resulting in vasodilation at inappropriate times. This increases blood flow to the skin that causes the warmth, sweating, and flushing that is typical of a hot flash.

This also explains the problems many women have with night sweats. The level of circulating estrogen in the body is usually lowest during sleep. This, on top of the already low level of estrogen in menopause, triggers the hypothalamus to cause vasodilation. This can result in poor sleep, likely contributing to daytime irritability and cognitive difficulties such as poor memory and concentration that are described by many menopausal women.

Some herbal preparations may be somewhat helpful with hot flashes. The most popular one is black cohosh, a member of the buttercup family. There have not been many well designed studies to assess its effectiveness, but anecdotal evidence seems to indicate is may be helpful and probably not harmful. Recall that herbs are not regulated by the FDA. If a woman is interested in using it, I usually recommend Remifemin® which is a standardized preparation. The antidepressant venlafaxine or Effexor® can also be helpful.

Estrogen replacement remains the most effective treatment for hot flashes. Treating menopausal symptoms with estrogen fell out of favor about 20 years ago when the results of the Women’s Health Initiative (WHI), a very large study of 160,000 postmenopausal women between 50 and 79, were announced. Taking estrogen appeared to increase the risk of breast cancer, cardiovascular disease, stroke and blood clots in the lungs.

However, an analysis of long-term follow up data of women in the WHI study published this May in the journal JAMA (bit.ly/4ah1MDY) showed that most women less than 60 years of age are at low risk when taking estrogen. The original findings seem to be biased due to the data being skewed by older women in the study.

Researchers compared mortality rates in women using hormone therapy to those taking a placebo. They found no difference in overall deaths regardless of age. There was also no significant change in heart attack risk for hormone users compared to the control group. The 2002 report suggesting increased heart risk was not confirmed in this new study. Stroke risk among young hormone users was relatively low — less than one extra case per 1,000 women using estrogen-progestin therapy and no excess risk with estrogen alone.

The two main types of hormone therapy had opposing effects on breast cancer. Taking estrogen alone, only suitable for women who’ve had a hysterectomy, lowered breast cancer risk. However, combination therapy with estrogen and progestin slightly increased risk, similar to the effect of one or two daily alcoholic drinks. Importantly, bone fracture risk was reduced 33 percent lower across all age groups. These findings offer a clearer picture of hormone therapy’s risks and benefits, allowing women to make informed decisions about its use.