New research is shedding some light on heat, specifically the hot flashes—what doctors call vasomotor symptoms—many women experience, sometimes as often as several times a day, due to menopause or after a hysterectomy. Though these symptoms are known to be triggered by hormonal changes, the exact mechanism and purpose has long been a mystery.
Only humans experience menopause, though all female primates become less fertile with age. However, while other primates remain fertile for their entire lives, humans can live to see their youngest children reach age 30, age 35, or even older. The difference isn’t in length of reproductive life but overall lifespan—most primates see fertility decline around the same time, but women live longer, allowing them to be there for children and grandchildren.
The new study, at Wayne State University in Michigan, looks at hot flashes as a neurological phenomenon, in contrast to studies that had focused on the skin sensation. The researchers used neuroimaging techniques to look at what is happening in the brain during the experience. What they found is that the brain stem, which is responsible for thermal regulation, shows activity before the hot flash begins, while the areas of the brain that are involved in sensations of skin and body temperature only become active after onset. That is strong evidence that hot flashes originate in the brain. A likely hypothesis is that the sudden reduction in amounts of estrogen causes changes in the brain, to which it responds by raising the body’s temperature.
If this is the case, it would explain why hormone therapy is so effective. Hormone replacement therapy administers estrogen and progesterone to replace the natural production, which slows at menopause. Hormone replacement is not recommended as a first-line treatment, however, because it can increase the risk of serious health complications, such as heart disease, stroke, dementia, and breast and endometrial cancer. A class of antidepressants called selective serotonin reuptake inhibitors has been found effective against vasomotor symptoms. Compounds found in soy and legumes may also provide some relief.