The Mediating Role of Brown Fat and Skeletal Muscle Measured by ¹⁸F‐Fluorodeoxyglucose in the Thermoregulatory System in Young Adults

Abstract

Objective This study aimed to examine whether brown adipose tissue (BAT) or skeletal muscle activity mediates the relationship between personal level of environmental temperature (Personal‐ET) and wrist skin temperature (WT). Moreover, we examined whether BAT and skeletal muscle have a mediating role between Personal‐ET and WT (as a proxy of peripheral vasoconstriction/vasodilation). Methods The levels of BAT were quantified by cold‐induced 18F‐fluorodeoxyglucose–positron emission tomography/computed tomography scan and measured the Personal‐ET and WT by using iButtons (Maxim Integrated, Dallas, Texas) in 75 participants (74.6% women). Results The study found that BAT volume and metabolic activity played a positive and significant role (up to 25.4%) in the association between Personal‐ET and WT. In addition, at the coldest temperatures, the participants with lower levels of WT (inducing higher peripheral vasoconstriction) had higher levels of BAT outcomes, whereas in warm temperatures, participants with higher levels of WT (inducing higher peripheral vasodilation) had lower levels of BAT outcomes. The study did not find any mediating role of skeletal muscle activity. Conclusions BAT volume and metabolic activity play a role in the relationship between Personal‐ET and WT. Moreover, the data suggest that there are two distinct phenotypes: individuals who respond better to the cold, both through nonshivering thermogenesis and peripheral vasoconstriction, and individuals who respond better to the heat.

Cold-Induced Thermogenesis Shows a Diurnal Variation That Unfolds Differently in Males and Females

“…The lower shivering temperature in females together with a stronger peripheral vasoconstriction (as estimated using the peripheral temperature gradient, that is, the forearm—fingertip temperature gradient) upon cold in the morning compared with the evening, suggests that women could tolerate cold temperatures better in the morning. Interestingly, increased peripheral vasoconstriction is associated with higher BAT activity in humans ( 36 ). Nevertheless, we did not observe differences in cold-induced EE between the morning and the evening in females.…”