•  
  •  
 

Abstract

Effect of Caffeine on Symptoms and Biomarkers of Gastrointestinal Injury After Physical Work in the Heat

MARISSA RAMIREZ, JONATHAN W. SPECHT, FABIANO T. AMORIM

Exercise Science Laboratory; Department of Health, Exercise, and Sport Sciences; University of New Mexico; Albuquerque, NEW MEXICO

Category: Doctoral

Advisor / Mentor: Amorim, Fabiano (amorim@unm.edu)

ABSTRACT

Several job industries require substantial prolonged physical exertion in hot environmental conditions which increases the risk of heat-related illnesses. Endotoxemia, a hallmark of exertional heat stroke, is defined by increased levels of circulating lipopolysaccharides, often caused by gastrointestinal (GI) injury and subsequent permeability. Caffeine is a stimulant frequently used among workers to improve concentration and mood, however, a common side effect is GI distress. Previous research also indicates that caffeine use prior to exercise in the heat may increase core temperature (Tcore). PURPOSE: To investigate the effect of ingesting a moderate dose of caffeine prior to physical activity in a hot environment on physiological strain and gastrointestinal injury and endotoxemia. METHODS: In a double-blind, randomized, crossover design, nine participants (6 females) were recruited for this study. A 120-minute protocol was completed in a heat chamber (35°, 53% R.H.), consisting of two, 1-hour cycles of 20-minutes walking on a treadmill at 40% VO2peak, 5-minutes of a low-intensity box-lifting activity, another 20-minutes walking at 40% VO2peak, and 10-minute seated rest. GI symptoms, heart rate (HR), and Tcore were recorded throughout. Serum concentrations of intestinal fatty acid binding protein (I-FABP) and lipopolysaccharide binding protein (LBP) were determined from pre- and post-trial blood samples. RESULTS: Peak Tcore was 0.2°C higher in the caffeine condition (38.2 ± 0.4°C) compared to placebo (38.0 ± 0.3°C) (p=0.02). A condition effect was observed (p=0.001) on HR, as peak HR was higher in the caffeine condition (152 ± 19 bpm) compared to placebo (140 ± 17 bpm) (p=0.01). There was a greater incidence of overall GI symptoms in caffeine condition (p=0.03), however caffeine did not have a significant effect on circulating markers of intestinal damage (I-FABP) or endotoxemia (LBP) (p>0.05). A time effect was observed for I-FABP, where concentrations increased from pre- to post-physical activity in the heat. CONCLUSION: These findings provide evidence that workers who perform physical activity and are exposed to hot environmental conditions may consider avoiding caffeine ingestion, in order to prevent hyperthermia and potential risk for exertional heat illness.

Download

Share

COinS
 
 

To view the content in your browser, please download Adobe Reader or, alternately,
you may Download the file to your hard drive.

NOTE: The latest versions of Adobe Reader do not support viewing PDF files within Firefox on Mac OS and if you are using a modern (Intel) Mac, there is no official plugin for viewing PDF files within the browser window.