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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.

SUBMITTER: Savastano DM

PROVIDER: S-EPMC2762153 | biostudies-literature | 2009 Nov

REPOSITORIES: biostudies-literature

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Adiposity and human regional body temperature.

Savastano David M DM Gorbach Alexander M AM Eden Henry S HS Brady Sheila M SM Reynolds James C JC Yanovski Jack A JA

The American journal of clinical nutrition 20090909 5

<h4>Background</h4>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.<h4>Objective</h4>The objective was to test the hypothesis that temperature in a heat-dissipating region of the hand is elevated in obese adults.<h4>Design</h4>Obese [body mass index (in kg/m(2)) > or = 30] and normal-weight (NW; body mass ...[more]

PMID: 19740972

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Project description:Light significantly improves alertness during the night (Cajochen, Sleep Med Rev, 11, 2007 and 453; Ruger et al., AJP Regul Integr Comp Physiol, 290, 2005 and R1413), but results are less conclusive at daytime (Lok et al., J Biol Rhythms, 33, 2018 and 589). Melatonin and core body temperature levels at those times of day may contribute to differences in alerting effects of light. In this experiment, the combined effect of daytime exogenous melatonin administration and light intensity on alertness, body temperature, and skin temperature was studied. The goal was to assess whether (a) alerting effects of light are melatonin dependent, (b) soporific effects of melatonin are mediated via the thermoregulatory system, and (c) light can improve alertness after melatonin-induced sleepiness during daytime. 10 subjects (5 females, 5 males) received melatonin (5 mg) in dim (10 lux) and, on a separate occasion, in bright polychromatic white light (2000 lux). In addition, they received placebo both under dim and bright light conditions. Subjects participated in all four conditions in a balanced order, yielding a balanced within-subject design, lasting from noon to 04:00 pm. Alertness and performance were assessed half hourly, while body temperature and skin temperature were measured continuously. Saliva samples to detect melatonin concentrations were collected half hourly. Melatonin administration increased melatonin concentrations in all subjects. Subjective sleepiness and distal skin temperature increased after melatonin ingestion. Bright light exposure after melatonin administration did not change subjective alertness scores, but body temperature and proximal skin temperature increased, while distal skin temperature decreased. Light exposure did not significantly affect these parameters in the placebo condition. These results indicate that (a) exogenous melatonin administration during daytime increases subjective sleepiness, confirming a role for melatonin in sleepiness regulation, (b) bright light exposure after melatonin ingestion significantly affected thermoregulatory parameters without altering subjective sleepiness, therefore temperature changes seem nonessential for melatonin-induced sleepiness, (c) subjective sleepiness was increased by melatonin ingestion, but bright light administration was not able to improve melatonin-induced sleepiness feelings nor performance. Other (physiological) factors may therefore contribute to differences in alerting effects of light during daytime and nighttime.

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Adiposity and human regional body temperature.

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Adiposity and human regional body temperature.

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