Minimal changes in environmental temperature result in a significant increase in energy expenditure and changes in the hormonal homeostasis in healthy adults

Abstract

Objective: Resting energy expenditure (EE) is a major contributor to the total EE and thus plays an important role in body weight regulation. Adaptive thermogenesis is a major component of EE in rodents, but little is known on the effects of exposure of humans to mild and sustainable reduction in environmental temperature.

Design: To characterize the dynamic changes in continuously measured resting EE, substrate utilization, and hormonal axes simultaneously in response to mild reduction in environmental temperature, we performed a cross-over intervention.

Methods: Twenty-five volunteers underwent two 12-h recordings of EE in whole room indirect calorimeters at 24 and 19 °C with simultaneous measurement of spontaneous movements and hormonal axes.

Results: Exposure to 19 °C resulted in an increase in plasma and urine norepinephrine levels (P<0.0001), and a 5.96% (P<0.001) increase in EE without significant changes in spontaneous physical activity. Exposure to the lower temperature resulted in a significant increase in free fatty acid levels (P<0.01), fasting insulin levels (P<0.05), and a marginal decrease in postprandial glucose levels. A small but significant (P<0.002) increase in serum free thyroxine and urinary free cortisol (P<0.05) was observed at 19 °C.

Conclusions: Our observations indicate that exposure to 19 °C, a mild and tolerable cold temperature, results in a predictable increase in EE driven by a sustained rise in catecholamine and the activation of counter-regulatory mechanisms.

Trial registration: ClinicalTrials.gov NCT00521729.

Figure 1

(A) Study protocol overview. The study was designed as a randomized, single blind, cross-over intervention. After enrollment, the volunteers received a weight maintenance diet for 2 days before undergoing 12-h respiration chamber and hormonal axes recording. After 36 h of recovery, the study volunteers underwent the same procedure at the second experimental temperature (see text for details). (B) Blood samples collection and procedures during a 12-h respiration chamber stay. Blood sampling was performed through an airtight sampling port every hour except during the first 2 h of the recording and the first 2 h after the meal when the sampling was performed every 30 min.

Figure 2

CONSORT chart. Study volunteers screening, accrual, temperature sequence allocation, and completion rate.

Figure 3

Mean energy expenditure rate in 21 participants over 12 h spent at 24 °C (left) and 19 °C (right). Data are presented as individual recordings and as box-whisker plots for all the 21 participants, 14 males (filled circles) and 7 females (open circles).

Figure 4

Mean and s.d. of 21 participants for energy expenditure (top panel), respiratory quotient (middle panel), and plasma norepinephrine levels (bottom panel) at 24 °C (gray line) and 19 °C (black line) over the 12-h time course of the study. The dotted line indicates meal consumption at 360 min.