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Coffee does not dehydrate

updated

Tags: random, water, debunkery, fun, controversy

Five articles on PainSci cite Killer 2014: (1) Anxiety & Chronic Pain(2) The Complete Guide to Chronic Tension Headaches(3) Water Fever and the Fear of Chronic Dehydration(4) Can Supplements Help Arthritis and Other Aches and Pains?(5) Chronic, Subtle, Systemic Inflammation

PainSci notes on Killer 2014:

Many people believe that coffee is dehydrating. To test this popular idea, 50 men drank four cups (200ml) of either coffee or water each day for three days while their diet and activity were controlled. There were no differences in their body mass, urine volume, and signs of hydration in the blood and urine (pee clarity, basically). If you can drink almost a litre of coffee a day and have no measurable effect on hydration, then it is not “dehydrating” to any meaningful degree. The authors reasonably concluded that coffee “provides similar hydrating qualities to water.”

original abstract Abstracts here may not perfectly match originals, for a variety of technical and practical reasons. Some abstacts are truncated for my purposes here, if they are particularly long-winded and unhelpful. I occasionally add clarifying notes. And I make some minor corrections.

It is often suggested that coffee causes dehydration and its consumption should be avoided or significantly reduced to maintain fluid balance. The aim of this study was to directly compare the effects of coffee consumption against water ingestion across a range of validated hydration assessment techniques. In a counterbalanced cross-over design, 50 male coffee drinkers (habitually consuming 3-6 cups per day) participated in two trials, each lasting three consecutive days. In addition to controlled physical activity, food and fluid intake, participants consumed either 4×200 mL of coffee containing 4 mg/kg caffeine (C) or water (W). Total body water (TBW) was calculated pre- and post-trial via ingestion of Deuterium Oxide. Urinary and haematological hydration markers were recorded daily in addition to nude body mass measurement (BM). Plasma was analysed for caffeine to confirm compliance. There were no significant changes in TBW from beginning to end of either trial and no differences between trials (51.5±1.4 vs. 51.4±1.3 kg, for C and W, respectively). No differences were observed between trials across any haematological markers or in 24 h urine volume (2409±660 vs. 2428±669 mL, for C and W, respectively), USG, osmolality or creatinine. Mean urinary Na(+) excretion was higher in C than W (p = 0.02). No significant differences in BM were found between conditions, although a small progressive daily fall was observed within both trials (0.4±0.5 kg; p<0.05). Our data show that there were no significant differences across a wide range of haematological and urinary markers of hydration status between trials. These data suggest that coffee, when consumed in moderation by caffeine habituated males provides similar hydrating qualities to water.

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