Total body water and its compartments are not affected by ingesting a moderate dose of caffeine in healthy young adult males.
Level 2 - randomized trial
Double-blind, randomized crossover trial in 30 healthy men
PubMed 23724879 · doi:10.1139/apnm-2012-0253
What was done
This double-blind, randomized crossover trial evaluated the effects of 4 days of moderate caffeine ingestion versus placebo on hydration compartments in 30 healthy, non-smoking men (aged 20–39 years) with low habitual caffeine intake (<100 mg/day). Participants completed two 4-day treatment periods separated by a 3-day washout: 5 mg/kg/day of caffeine versus maltodextrin placebo. Total body water (TBW) was measured via deuterium oxide dilution, extracellular water (ECW) via sodium bromide dilution, and intracellular water (ICW) was calculated as TBW minus ECW. Dual-energy X-ray absorptiometry, accelerometry, and dietary logs were used to assess body composition, physical activity, and water intake.
What was found
No significant main effects or treatment-by-time interactions were observed for TBW, ECW, or ICW between the caffeine and placebo conditions (p > 0.05). Changes in body water compartments were also unrelated to fat-free mass, physical activity levels, or daily water intake (p > 0.05). The abstract reports no absolute numerical values or confidence intervals.
Why it matters
Using direct dilution techniques, this study confirms that moderate caffeine intake (roughly equivalent to 5 cups of espresso per day) does not disrupt fluid balance or compartment distribution in healthy, active men over short durations.
Limits
The sample was restricted to young, healthy, low-caffeine-consuming males, limiting generalizability to women, older populations, or chronic heavy consumers. The intervention lasted only 4 days, sample size was small (n = 30), and specific numerical values were not provided in the abstract.