Abstract
Low levels of caffeine ingestion do not induce dehydration at rest, while it is not clear if larger doses do have an acute diuretic effect. The aim of the present investigation was to examine the acute effect of low and high levels of caffeine, via coffee, on fluid balance in habitual coffee drinkers (at least one per day) at rest. Ten healthy adults (eight males and two females; age: 27 ± 5 years, weight: 89.5 ± 14.8 kg, height: 1.75 ± 0.08 m, and body mass index: 29.1 ± 4.4 kg m-2) ingested 200 mL of water (W), coffee with low caffeine (3 mg kg-1, LCAF), or coffee with high caffeine (6 mg kg-1, HCAF) on three respective separate occasions. All sessions were performed at 09:00 in the morning in a counterbalanced, crossover manner, at least 5 days apart. Subjects remained in the laboratory while urine samples were collected every 60 min for 3 h post ingestion. Absolute caffeine consumption was 269 ± 45 and 537 ± 89 mg for the LCAF and HCAF, respectively. Coffee ingestion at the HCAF trial induced greater diuresis during the 3-h period (613 ± 101 mL, P < 0.05), when compared to W (356 ± 53 mL) and LCAF (316 ± 38 mL). In addition, cumulative urinary osmotic excretion was significantly greater in the HCAF (425 ± 92 mmol, P < 0.05), as compared to the W (249 ± 36 mmol) and LCAF (177 ± 16 mmol) trials. The data indicate that caffeine intake of 6 mg kg-1 in the form of coffee can induce an acute diuretic effect, while 3 mg kg-1 do not disturb fluid balance in healthy casual coffee drinking adults at rest.
Highlights
Maintaining fluid balance is vital for health and well-being [1, 2]
In 2015, the European Food Safety Authority concluded caffeine ingestion up to 6 mg kg−1 of body weight will not induce diuresis; their conclusion only pertained to caffeine ingestion coupled with endurance exercise [7]
HCAF trial resulted in higher urinary output during most time-points when compared to LCAF and W trials (P < 0.05)
Summary
Maintaining fluid balance is vital for health and well-being [1, 2]. Fluid balance can be compromised by failing to consume sufficient fluid to meet water losses, leading to hypohydration. The guidelines for consuming caffeinated beverages, such as coffee, and their effect on body fluid balance are less clear. The United States Food and Drug Administration recommends no more than 400 mg day−1 of caffeine in healthy adults equating to approximately three to four cups of coffee. This is a standard amount not relative to body weight, which has been shown to effect caffeine metabolism [5]. The aim of the present investigation was to examine the acute effect of low and high levels of caffeine, via coffee, on fluid balance in habitual coffee drinkers (at least one per day) at rest
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