Nicotine exacerbates exertional heat strain in trained men: A randomized, placebo-controlled, double-blind study.

Abstract

To determine if using nicotine exacerbates exertional heat strain through an increased metabolic heat production (Hprod) or decreased skin blood flow (SkBF), ten nicotine-naïve trained males (37±12 y; VO2peak: 66±10 ml·min-1·kg-1) completed four trials at 20°C and 30°C following overnight transdermal nicotine (7mg·24h-1) and placebo use in a crossover, double-blind design. They cycled for 60 min (55% VO2peak) followed by a time-trial (~75% VO2peak) during which measures of gastro-intestinal (Tgi) and mean weighted skin ( sk) temperatures, SkBF, Hprod, and mean arterial pressure (MAP) were made. The difference in ∆Tgi between nicotine and placebo trials was greater during 30°C (0.4±0.5°C) than 20°C (0.1±0.7°C), with sk higher during nicotine than placebo trials (0.5±0.5°C, p=0.02). SkBF became progressively lower during nicotine than placebo trials (p=0.01) and progressively higher during 30°C than 20°C trials (p<0.01); MAP increased from baseline (p<0.01) and remained elevated in all trials. The difference in Hprod between 30°C and 20°C trials was lower during nicotine than placebo (p=0.01) and became progressively higher during 30°C than 20°C trials with exercise duration (p=0.03). Mean power output during the time-trial was lower during 30°C than 20°C trials (24±25 W, p=0.02), and although no effect of nicotine was observed (p>0.59) two participants (20%) were unable to complete their 30°C nicotine trials as one reached the ethical limit for Tgi (40.0°C) whilst the other withdrew due to "nausea and chills" (Tgi=39.7°C). These results demonstrate that nicotine use increases thermal strain and risk of exertional heat exhaustion by reducing SkBF.