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ACUTE EFFECTS OF CAFFEINE CONSUMPTION ON HEART RATE VARIABILITY AT REST

Abstract

ACUTE EFFECTS OF CAFFEINE CONSUMPTION ON HEART RATE VARIABILITY AT REST

J.E. Kumanchik, J.R. McNeal, and N.H. Lawton

Eastern Washington University, Cheney, WA

The cardiovascular system (CVS) is primarily controlled by the autonomic nervous system (ANS). Heart rate variability (HRV) is considered a balance between sympathetic and parasympathetic activity of the ANS that regulates heart rate, and thus a determinant of cardiovascular health. Therefore, measurement of HRV can provide insight into the autonomic function of the CVS and factors that influence it, such as caffeine consumption. PURPOSE: This study sought to determine the acute effects of caffeine consumption on HRV at rest. METHODS: A group of 23 apparently healthy male and female adults (21-27 years) were used for this study. Following 5 min of quiet sitting, subjects underwent an initial electrocardiogram (ECG) recording at rest for 3 min, using a 3-lead ECG. Subjects then consumed a dosage of caffeine equivalent to 2 mg per 1 kg of body mass using caffeinated jellybeans. Thirty minutes following ingestion, subjects underwent a second ECG recording at rest for 3 min. From the ECG record, duration between successive R-R waves was measured to determine HRV before and after caffeine consumption. A paired-samples t-test was conducted to compare HRV at rest between no caffeine (NC) and caffeine (C) conditions. Two independent-samples t-tests were conducted to determine if there were significant differences in HRV at rest in NC and C conditions between sexes. RESULTS: All HRV data are reported in the unit of milliseconds (msec). Coefficient of variation (CV) is also reported. There was a significant difference in HRV between NC (.76 ± .13 msec; CV = 17.1%) and C (.81 ± .15 msec; CV = 18.5%) conditions (p < .001). There was no significant difference in HRV between sex in the NC condition (Male = .77 ± .14 msec, CV = 18.1%; Female = .75 ± .13 msec, CV = 17.3%; p = .689) or the C condition (Male = .83 ± .15 msec, CV = 18.07%; Female = .79 ± .15 msec, CV = 18.9%; p = .547). CONCLUSION: These data suggest caffeine does have an effect on HRV at rest. Specifically, the results from this study suggest that caffeine consumption decreases HRV at rest, regardless of sex. Researchers or clinicians using HRV as a diagnostic tool should be aware that caffeine ingestion can reduce HRV, and should consider controlling for caffeine ingestion in their protocols.

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