Abstract
Retrospective studies suggest that women have more active brown adipose tissue (BAT) than men, but little is known of the effect of fluctuating sex steroids across the menstrual cycle on thermogenesis in women. To characterise the effects of sex and sex steroids on BAT activity we recruited healthy weight men (n = 14) and women at two stages of the menstrual cycle (luteal, n = 9; follicular, n = 11). Infrared thermography measured supraclavicular temperature to index BAT thermogenesis in response to both cold (immersion of one hand in water at 15°C) and meal (Ensure, 10 kcal/kg body weight) stimuli. Adaptive BAT temperature responses were greater (P < 0.05) in women than men, irrespective of stage of menstrual cycle. Whereas during cold exposure, the increase in BAT temperature was abrogated (P < 0.05) in women during follicular phase compared to men and women during luteal phase. Plasma concentrations of progesterone, 17β-estradiol, testosterone and cortisol were measured. Regression analyses demonstrated that baseline BAT temperature was positively correlated (P < 0.05) with progesterone levels, but was inversely associated (P < 0.05) with cortisol concentration. Both cold- and meal-induced changes in BAT temperature mildly correlated (P = 0.07; P < 0.05) with 17β-estradiol levels, but not with testosterone concentrations. Baseline supraclavicular temperature is elevated in women during the luteal phase of the menstrual cycle, which correlated with elevated progesterone concentrations. Women exhibited greater thermogenic responses than men, irrespective of the state of the menstrual cycle, which was associated with plasma levels of 17β-estradiol. We conclude that sex steroids may regulate BAT thermogenesis in healthy adults.
Highlights
Thermogenesis contributes to approximately 10% of total energy expenditure in lean individuals [1]
Retrospective studies indicate that women may possess more functional beige adipose tissue (BAT) than men [12, 24, 25], but no studies have heretofore determined whether BAT activity changes across the menstrual cycle in women
The present study employed infrared thermography to demonstrate that BAT heat production in response to both cold exposure and meal consumption was greater in women than in men
Summary
Thermogenesis contributes to approximately 10% of total energy expenditure in lean individuals [1]. Brown and beige adipose tissue (BAT) as well as skeletal muscle contribute to total thermogenic capacity [2]. BAT is located in the supraclavicular, neck, epicardial, peri-renal and para-spinal adipose depots [3]. In the neck and supraclavicular regions, adipose tissue contains a heterogeneous population of white, brown and beige adipocytes [4], with the latter two cell types being capable of thermogenesis. In humans chronic activation of BAT via repeated cold exposure increases energy expenditure and decreases adiposity [8]. Cold-induced BAT activation increases glucose and triglyceride clearance and improves insulin sensitivity in adults [9, 10]. It remains contentious as to the precise physiological role and importance of BAT in metabolism and energy expenditure in humans [11]
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