Adiposity and human regional body temperature1–3

Background: Human obesity is associated with increased heat pro-duction; however, subcutaneous adipose tissue provides an insulat-ing layer that impedes heat loss. To maintain normothermia, therefore, obese individuals must increase their heat dissipation. Objective: The objective was to test the hypothesis that temperature in a heat-dissipating region of the hand is elevated in obese adults. Design: Obese [body mass index (in kg/m2) 30] and normal-weight (NW; body mass index = 18–25) adults were studied under thermoneutral conditions at rest. Core body temperature was mea-sured by using ingested telemetric capsules. The temperatures of the third fingernail bed of the right hand and of abdominal skin from an area 1.5 cm inferior to the umbilicus were determined by using infrared thermography. Abdominal skin temperatures were also measured via adhesive thermistors that were placed over a promi-nent skin-surface blood vessel and over an adjacent nonvessel loca-tion. The groups were compared by analysis of covariance with age, sex, race, and room temperature as covariates. Results: Core temperature did not differ significantly between the 23 obese and 13 NW participants (P = 0.74). However, infrared thermography–measured fingernail-bed temperature was signifi-cantly higher in obese subjects than in NW subjects (33.9 6 0.7 C compared with 28.6 6 0.9C; P, 0.001). Conversely, infrared thermography–measured abdominal skin temperature was signifi-cantly lower in obese subjects than in NW subjects (31.8 6 0.2C compared with 32.8 6 0.3C; P = 0.02). Nonvessel abdominal skin temperatures measured by thermistors were also lower in obese subjects (P = 0.04). Conclusions: Greater subcutaneous abdominal adipose tissue in obese adults may provide a significant insulating layer that blunts abdominal heat transfer. Augmented heat release from the hands may offset heat retention in areas of the body with greater adiposity, thereby helping to maintain normothermia in obesity. This trial was registered at clinicaltrials.gov as NCT00266500. Am J Clin Nutr doi: 10.3945/ajcn.2009.27567