Adiposity and human regional body temperature

Abstract

Background: Human obesity is associated with increased heat production; however, subcutaneous adipose tissue provides an insulating 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/m(2)) > or = 30] and normal-weight (NW; body mass index = 18-25) adults were studied under thermoneutral conditions at rest. Core body temperature was measured 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 prominent skin-surface blood vessel and over an adjacent nonvessel location. 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 significantly higher in obese subjects than in NW subjects (33.9 +/- 0.7 degrees C compared with 28.6 +/- 0.9 degrees C; P < 0.001). Conversely, infrared thermography-measured abdominal skin temperature was significantly lower in obese subjects than in NW subjects (31.8 +/- 0.2 degrees C compared with 32.8 +/- 0.3 degrees C; 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.

Figures

FIGURE 1

Abdominal (left) and right-hand (right) thermograms of an obese female (A) and a normal-weight female (B). Arrows indicate the location 1.5 cm inferior to the umbilicus selected for image analysis. Temperatures are represented by colors, as indicated by the gradient on the right.

FIGURE 2

A: Mean (±SE) fingernail-bed temperatures, adjusted as indicated in Subjects and Methods, measured by infrared thermography. B: Adjusted mean (±SE) difference between fingernail-bed temperature and core temperature. C: Adjusted mean (±SE) abdominal skin temperatures 1.5 cm inferior to the umbilicus determined by infrared thermography. D: Adjusted mean (±SE) differences between abdominal skin temperature and core temperature. Differences in temperatures between the normal-weight (NW; n = 13) and obese (OB; n = 23) participants were determined by using ANCOVA with age, race, sex, and room temperature as covariates.

FIGURE 3

Mean (±SE) abdominal skin temperatures, adjusted as indicated in Subjects and Methods, measured with dermal thermistor patches. Infrared thermography was used to guide patch placement; the thermistor of one patch was placed directly over the warmest location on the abdomen (warm) and the thermistor of another patch was placed over the coolest location (cool) in proximity to the warm patch. Differences in temperature between the normal-weight (NW; n = 13) and obese (OB; n = 23) participants were determined by using ANCOVA with age, race, sex, and room temperature as covariates.

FIGURE 4

Mean (±SE) fingernail-bed temperatures, adjusted as indicated in Subjects and Methods, measured by infrared thermography in response to a mild cold (20 °C) challenge of the hand. Differences in temperature between the normal-weight (NW; n = 13) and obese (OB; n = 23) participants were determined by using repeated-measures ANCOVA with age, sex, race, and room temperature as covariates. No significant group × time interaction was observed (P = 0.47).

FIGURE 5

Fingernail-bed temperature (A) and abdominal skin temperature 1.5 cm inferior to the umbilicus (B) relative to the percentage of total body mass from fat in normal-weight (n = 13) and obese (n = 23) participants. Measured temperatures were adjusted for relevant covariates (age, sex, race, and room temperature) in the regression model.