Caffeine Excretion Rates of a Single Dose of 300 Milligrams of Caffeine in College Students
Caffeine demonstrates ergogenic benefits with a dose of 3 to 6 mg/kg of body weight. The NCAA bans caffeine in concentrations over 15 µg/ml in urine. However, the amount of caffeine an individual can consume before reaching the legal limit is unclear.
Purpose: To assess the rate of caffeine excretion in different individuals using a single dose of 300 mg.
Methods: IRB approved this research and 19 college students (4 males; 15 women) agreed to participate and signed informed consents. The participants refrained from caffeine 4 hours prior to the testing period. Each student consumed 300 mg of caffeine with 12 oz. of Crystal Light, representing a range from 3.4 to 5.0 mg/kg. Urine samples were collected 1, 2, 3, and 4 hours post consumption. Specific gravity and urine volumes were recorded for each sample to assess hydration status. An ELISA Assay was used to analyze the caffeine concentration. A link to an online survey was emailed to the collegiate population assessing physical activity, caffeine products used and reasons for caffeine consumption. Repeated one-way ANOVA and bivariate analysis was used to assess significance.
Results: Peak caffeine concentrations were reached at hour 3 (10.8 +/- 3.3 µg/ml). The mean caffeine concentration at hour 1 was 7.8 +/- 3.8 at hour 2 was 10.3 +/-2.8 at hour 3 was 10.8 +/-3.3 at hour 4 was 10.1 +/-4.2 and only hour 1 and 2 were significantly different (p = 0.016). Five females (148.2 +/- 6.6 lbs.) exceeded the NCAA upper limit. The females received approximately 4.5 mg of caffeine /kg of body weight. The participants came to the lab well hydrated (specific gravity, 1.0053 +/- 0.0049) and stayed well hydrated (1.0075 +/- 0.0043) throughout the study. Caffeine use was reported by 89.2% of individuals (n=351), but only 9.7% of the respondents reported using a pre-workout supplement and only 11% use caffeine for its ergogenic benefits. Males were more likely than females to use caffeinated pre-workout supplements and use caffeine to enhance performance (16% males; 4% females).
Conclusions: A dose of 300 mg of caffeine resulted in 21.5% of the individuals exceeding the 15-µg/ml NCAA threshold, approximately the content of a 16oz Starbucks.
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