My hot flashes feel like a heat wave sweeping over me, leaving me soaked in sweat and freezing. Why does this happen only in mid-life, and are there any risks if left untreated?

Your Question: My hot flashes feel like a heat wave sweeping over me, leaving me soaked in sweat and freezing. Why does this happen only in mid-life, and are there any risks if left untreated?

Our Response: As humans, our primary forms of body heat dissipation are convection and evaporation through sweating. Both of these responses are activated by sympathetic cholinergic nerve activity, which causes increased blood flow to our skin vessels. In warm climates, the body acclimates to these chronic responses in order to prevent dehydration (from sweating) or hypotension (from redistribution of blood from our core to our periphery). By contrast, hot flashes (called vasomotor symptoms or VMS) are an acute event, which, if untreated, may actually indicate early evidence of cardiovascular risk.

The current theory states that hot flashes originate in the hypothalamus and are suppressed by high levels of ovarian estradiol. During the reproductive years, women tolerate variations in environmental temperatures of about 0.4 degrees (called thermal tolerance) without activating their heat-cooling systems. During the menopause transition, the premise has been that decline in ovarian estradiol is associated with a loss of thermal tolerance. Newer studies, however, may explain why, despite loss of ovarian estradiol for all women, only certain women experience hot flashes. These studies of cardiovascular function during a hot flash suggest that women in the menopause transition who are likely to encounter hot flashes in the future may exhibit different responses of their autonomic nervous system, and those differences may actually exist before hot flashes are experienced clinically.

During the menopause transition, hot flashes are associated with an increased heart rate and, for some women, a reduced ability of the peripheral blood vessels to dilate, both of which reflect a withdrawal of sympathetic cholinergic control and placing an additional burden on their cardiac function.

These preliminary studies suggest that vasomotor symptoms are not simply loss of estradiol, but may be preceded by dysregulation of the autonomic nervous system for a certain population of women. It also suggests that these neurologic changes may begin early, even before menopause is reached or hot flashes appear. Because estradiol supplementation in menopause successfully reduces the sensations of hot flashes, its actions may be to counter the negative impact of the dysregulated autonomic nervous system.

James Woods | 2/28/2020

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