Figure 4.

Sex differences in thermoregulation have an impact on energy homeostasis. Red and blue represent women and men, respectively. (A) Core temperature (Tc) levels are higher in women than in men and vary across the ovarian cycle, associated to changes in progesterone:estrogens circulating concentrations. In the luteal phase there is an increase of ≈ 0.5 °C, when compared to the follicular phase. (B) A representation of the thermoneutral zone (TNZ) in both sexes. The increase of Tc levels in women is a regulated process, as shown by the shifts in thermoregulatory thresholds of effector mechanisms toward the defense of this higher temperature. Accordingly, cold output mechanisms will be activated at higher ambient temperatures in women than in men. (C) At mild temperatures a greater BAT and WAT browning thermogenesis will be observed in women compared to men, which will increase energy expenditure. Sexual hormones play a central role in these sex differences, with estrogens as principal stimulators of BAT activity and WAT browning and regulators of vasomotor control, and progesterone as a thermogenic signal acting at the set-point(s) in the hypothalamus.