Endocrine Abstracts

Background: Infrared thermography (IRT) can assess human brown adipose tissue (BAT) activity non-invasively. However, it remains unclear if skin temperature is altered in obesity. We compared skin temperatures of lean and obese individuals following cold exposure and studied its relationship with energy expenditure (EE).

Methods: 10 lean (age 28.3±2.1y, BMI 21.5±0.4kg/m²) and 10 obese (age 28.2±2.1y, BMI 36.2±1.3kg/m²) gender-matched subjects were placed in a warm (thermoneutral, 23-24°C) followed by cold room (16-17°C) for 2 hours each. Skin temperature was obtained through IRT every 15-30 minutes at 2 locations; supraclavicular fossae (T_SCV), where human BAT is located and mediastinum (T_med), which served as a reference for comparison. EE was measured by indirect calorimetry hourly. Data are expressed as mean±SEM.

Results: EE was higher in obese subjects but increased following cold exposure only in lean group (by 158±47 vs 86±52kcal/24h). Core (tympanic) temperatures in warm and cold were similar between groups. T_SCV and T_med were higher at both temperatures in lean subjects. Cold exposure induced a greater decrease in T_med (2.7±0.2°C vs 1.7±0.2°C) and T_SCV (1.4±0.2°C vs 1.0±0.1°C) in obese than lean subjects, increasing the cold-induced temperature differential between supraclavicular and mediastinal regions in obese subjects. T_med and T_SCV during both temperature conditions negatively correlated with BMI, body weight and fat mass. Cold-induced thermogenesis (CIT) negatively correlated with EE at thermoneutrality (P < 0.05) and, in lean subjects, tended to correlate with the change in T_scv during cold exposure (P = 0.1).

Conclusions: Obese subjects have lower skin temperatures even at thermoneutrality, potentially due to adipose tissue insulation. This may confound measurements of BAT activity if not taken into account. Reduced CIT in obesity during cold exposure may be due to reduced requirement for thermogenesis from increased basal EE.