The Supraclavicular Skin Temperature Response to Mild Cold Stimulation is Dependent on Ambient Temperature

Abstract

Purpose: This study investigated the basal activity, and cold-induced thermogenic response, of supraclavicular brown adipose tissue (BAT) under warm (23˚C) and cool (18˚C) ambient conditions using supraclavicular skin temperature as a measure of BAT activity. As a highly metabolic, heat-producing tissue, it has been hypothesised that under-active/dysfunctional BAT may underlie a pathological energy imbalance leading to obesity. Methods: Five lean, healthy participants underwent infrared thermography (IRT) of supraclavicular BAT before, and during, mild cold exposure (single-hand immersion in cool water at 20˚C), once at 18˚C and once at 23˚C. Energy expenditure (EE) was measured simultaneously using indirect calorimetry, and mean skin temperature (TMSK) was calculated at 1-minute intervals in parallel to IRT using wireless data loggers. Results: Following 30 minutes of hand cooling, supraclavicular skin temperature (TSCR) rose significantly from baseline at an ambient temperature of 23˚C (∆TSCR: 0.17 ± 0.03˚C, P < 0.01), and EE rose by 0.22 ± 0.02 kJ/min, P < 0.001. At an ambient room temperature of 18˚C, TSCR after hand cooling was similar to baseline, and EE remained unchanged. The TMSK response was indicative of a systemic vasoconstrictive response of similar magnitude in both warm and cool ambient temperatures. Conclusions: At 18˚C in light clothing, BAT may already be maximally stimulated at baseline, and respond minimally to additional cold exposure. Ambient temperature is recognised as a determinant of glucose uptake in BAT. In this study, we show, that it also modulates the TSCR response to further localised cold-stimulation, indicating an effect on BAT thermogenesis.