Influence of aerobic fitness, activity level, and smoking history on the acute thermic effect of nicotine.

Individual variability in sensitivity to the acute thermic effects of nicotine has been difficult to study because of methodological limitations in the use of smoking to manipulate nicotine dose. This study examined the influence of smoking history, body composition, and, in a subset of subjects, aerobic fitness and physical activity on the thermic effect of nicotine using a measured-dose nasal spray procedure. Following overnight fasting and smoking abstinence, 38 healthy male smokers were intermittently administered a nicotine dose corrected for body weight (15 micrograms/kg, approx. 1.1 mg for average subject) or placebo on separate occasions in a within-subjects study. Indirect calorimetry was used to assess resting energy expenditure (REE) before and after dosing. Acute thermic response to nicotine ranged from -4.3 to +10.8 kcal/h (-5.4% to +12.6% of REE). Thermic response to nicotine was correlated significantly with aerobic fitness (r = 0.58, p < 0.005), physical activity (r = 0.44, p < 0.05), and number of pack-years of smoking (r = 0.43, p < 0.01). Thermic response was marginally correlated with percent body fat (r = -0.23, p < 0.10), but not with body weight (r = 0.04), percent of ideal weight for height (r = -0.10), or lean body mass (r = 0.05). These results indicate that male smokers higher in fitness and activity and with greater smoking exposure histories may experience greater increases in energy expenditure as a result of nicotine intake via smoking. Consequently, variability in these characteristics could help account for some of the variability in weight gain after stopping smoking.