Caffeine With and Without Sugar: Individual Differences in Physiological Responses During Rest
Rush Elaine Journal of Caffeine Research. December 2014, 4(4): 127-130.
Background: The consumption of caffeine with and without sugar is endemic, but little is known about variation in individual physiological responses at rest. We have previously shown that the ingestion of caffeine with sugar increased the rate of carbon dioxide production more than when sugar alone was consumed.
Objective: The aim of this study was to determine the effect of the ingestion of caffeine, sugar, and caffeine with sugar on carbon dioxide production and heart rate.
Methods: In a crossover three-treatment design, 12 participants reported fasting on three separate days. Treatments were 1.33 mg/kg body weight caffeine only, 0.4 g/kg body weight sugar only, and caffeine with sugar. Breath-by-breath measurements of respiratory gas exchange and heart rate were recorded for 30 min before and after treatments. Data visualization techniques were used to examine the patterns of response.
Results: Carbon dioxide production increased or remained the same with all three treatments. Caffeine alone slowed the heart rate of eight participants and remained the same for four participants. Sugar alone either increased (n=8) or did not change the heart rate (n=4). Caffeine with sugar either decreased (n=5), did not change (n=6), or increased the heart rate (n=1). The intraindividual variability in response to treatments did not show a consistent pattern and could not be associated with habitual caffeine consumption, gender, or physical activity level.
Conclusions: The physiological response to caffeine with and without sugar varied widely. Effects of caffeine phenotypes, physical activity levels, habitual intake, and metabolic responses, including markers of de novo lipogenesis, need further investigation.
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