Age-related changes in how the brain responds to the female sex hormone estrogen may be involved in a woman's transition through menopause says a new study. The study - published in the Journal of the American Medical Association - provides new insights about hormonal influences on symptoms such as hot flashes and night sweats experienced by some women in the menopause transition.
"Throughout a woman's reproductive life, there are not only age-related changes in estrogen levels, but also differences in how her body responds to given levels of estrogen. Researchers have been trying to understand how and why these changes take place," says project director Sherry Sherman. "Hormone patterns found in this study could mean that, with age, a part of a woman's brain which regulates reproductive hormone levels may become less sensitive to estrogen. Other study findings suggest that the decreases in sensitivity can lead to significantly increased hot flashes and night sweats."
The study followed more than 3,300 women, between the ages 42-52, as they experienced the changes associated with approaching menopause. Through this sampling, the study characterized the fluctuations in hormones such as estrogen, which is produced by the ovary, and fluctuations in other hormones such as luteinizing hormone (LH), which is produced by the pituitary, a gland at the base of the brain. These reproductive hormones are needed for normal menstrual cycles and to prepare the body for pregnancy.
In this study, the hormone levels in some of these middle-aged women reflected a likely insensitivity to estrogen in the brain. Three different patterns of hormone fluctuations were evident in women who did not ovulate: the first group of women had a surge of LH - what the researchers called an "appropriate" response to increases in estrogen. In a second group, the same increases in estrogen were not associated with a surge in LH. In the third group, estrogen levels early in the cycle were similar to those of groups 1 and 2, but, unlike those two groups, did not show further increases. The LH levels in this group did not show a surge and were higher for most of the cycle than in the other groups. The hormonal patterns in groups 2 and 3 suggest different kinds of reduced sensitivity to estrogen (or abnormal estrogen "feedback") in the brain.
The women in the third group had significantly more hot flashes and night sweats than women in the other two groups. These findings suggest that the hormonal pattern associated with increases in symptoms reflects alterations in the sensitivity to estrogen in the brain. Additional follow-up of the women as they experience their final menstrual period and become postmenopausal is needed to further clarify the hormonal changes underlying the menopause transition as well as those causing hot flashes.