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Thermoneutral conditions

0.832±0.039

0.833±0.049

0.94

Cold exposure

0.798±0.027

0.789±0.031

0.46

Thermoneutral conditions

36.7±0.3

36.6±0.2

0.49

Cold exposure

36.8±0.3

36.8±0.2

0.80

Variable

Lean Group (N = 10)

Overweight or Obese Group (N =14)

P Value, Lean vs. Obese

P Value, 22°C vs. 16°C

BAT activity (kBq)† BAT volume (cm3)† Resting metabolic rate (MJ/24 hr)

428±394 130±98

102±93 77±69

0.007 0.14

Lean Subjects

Overweight or Obese Subjects

<0.001

<0.001

Thermoneutral conditions Cold exposure Respiratory quotient (VCO2/VO2)‡

8.46±0.93 9.62±1.36

8.16±0.29 9.56±0.66

0.27 0.89

0.009

<0.001

Thermoneutral conditions

32.5±0.6

32.4±0.4

0.64

Cold exposure

29.2±0.8

28.7±0.6

0.06

Gradient, core and skin Thermoneutral conditions Cold exposure Gradient, arm–finger Thermoneutral conditions Cold exposure

4.2±0.6 7.5±0.8

4.3±0.4 8.1±0.7

0.86 0.08

<0.001

<0.001

−1.9±1.4 3.4±2.8

−3.5±1.7 4.6±2.8

0.03 0.29

<0.001

<0.001

  • *

    Plus–minus values are means ±SD. BAT denotes brown adipose tissue, VCO2 volume of carbon dioxide produced, and VO2 volume of oxy­

gen consumed.

  • BAT activity and BAT volume were measured after cold exposure.

  • Both VCO2 and VO2 are measured in liters per minute.

T h e ne w engl a nd jour na l o f medicine

Table 2. Activity and Volume of Brown Adipose Tissue, Resting Metabolic Rate Adjusted for Fat-free Mass and Body Temperature under Thermoneutral Conditions (22°C) and after 2 Hours of Cold Exposure (16°C).*

0.06

0.02

<0.001

<0.001

Body temperature (°C) Core

Skin

tissue tended to be lower in the overweight or obese subjects than in the lean subjects, but the difference was not significant (P=0.14). Only one subject had no 18F-FDG uptake in areas of adi- pose tissue. This subject had the highest BMI (38.7) and percentage of body fat (41.8%). In all subjects with brown-adipose-tissue activity, the area with the most evidence of activity was the supraclavicular region (Fig. 1). However, other sites also had substantial putative brown-adipose- tissue activity.

and 0 kBq in thermoneutral conditions, in Sub- ject 3 at 587.2 kBq during cold exposure and 0 kBq in thermoneutral conditions, and in Subject 4 at 250.0 kBq during cold exposure and 0 kBq ther- moneutral conditions.

Studies of brown adipose tissue obtained from the supraclavicular region during surgery in the patient with multinodular goiter revealed the pres- ence of UCP1 (Fig. 2). The protein was not detect- ed in white adipose tissue taken from the same region in this patient.

There was no detectable brown-adipose-tissue activity in the three subjects who were retested under thermoneutral conditions (Fig. 1E). Brown- adipose-tissue activity was recorded in Subject 2 (Fig. 1A) at 856.5 kBq during exposure to cold

On exposure to cold, all subjects had an insu- lative response (a reduction of skin temperature relative to core temperature) and a metabolic re- sponse (an increase in heat production) (Table 2). Body core temperature increased slightly in re-

1504

n engl j med 360;15

nejm.org

april 9, 2009

The New England Journal of Medicine Downloaded from nejm.org on February 3, 2015. For personal use only. No other uses without permission. Copyright © 2009 Massachusetts Medical Society. All rights reserved.

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