No evidence of dehydration with moderate daily coffee intake: a counterbalanced cross-over study in a free-living population.
Level 2 - randomized trial
Individual counterbalanced crossover trial
PubMed 24416202 · doi:10.1371/journal.pone.0084154
What was done
In a counterbalanced cross-over study, 50 male habitual coffee drinkers (3–6 cups/day) participated in two 3-day trials with standardized physical activity, food, and fluid intake. Participants consumed either 4 × 200 mL of coffee providing 4 mg/kg caffeine daily or 4 × 200 mL of water. Total body water was assessed pre- and post-trial using deuterium oxide dilution. Daily measurements included nude body mass, haematological hydration markers, and urinary markers (24-hour volume, specific gravity, osmolality, creatinine, and sodium), with plasma caffeine measured to verify compliance.
What was found
Total body water did not differ between coffee and water trials (51.5 ± 1.4 kg vs. 51.4 ± 1.3 kg) or change from baseline. No significant differences were observed between trials in 24-hour urine volume (2409 ± 660 mL for coffee vs. 2428 ± 669 mL for water), urine specific gravity, urine osmolality, urine creatinine, or haematological markers. Mean urinary sodium excretion was significantly higher during the coffee trial (p = 0.02). Body mass did not differ between conditions, though both trials showed a small daily reduction (0.4 ± 0.5 kg, p < 0.05).
Why it matters
This study provides direct experimental evidence that moderate coffee consumption contributes to daily fluid requirements and does not cause dehydration in habitual consumers under standard living conditions.
Limits
The cohort was restricted to 50 healthy, caffeine-habituated adult males; results may not apply to non-habitual consumers, females, or clinical populations. The duration of each intervention was short (3 days), and the trial tested only one moderate dose (4 mg/kg caffeine).