Hydration status and the diuretic action of a small dose of alcohol.

AIM: This study was conducted to examine the effect of consuming a dilute alcohol solution (weak beer) on urine production in euhydrated and hypohydrated individuals.

METHODS: Twelve males completed an intermittent cycle protocol in hot (35.1 +/- 0.3 degrees C), humid (68 +/- 2%) conditions to dehydrate by 1.9 +/- 0.3% body mass in the evening. Twice they were then fed and rehydrated, while on two other occasions they were fed the same meal but remained hypohydrated. The following morning they were given 1 l of beer to drink. On two occasions the beer was alcohol-free, while on the other two occasions the same beer contained 4% ethanol. Participants remained in the laboratory for monitoring over the subsequent 4 h. Blood and urine samples were taken prior to dehydration, prior to drink administration and once every hour of the monitoring period.

RESULTS: No difference existed in the volume of urine produced between the alcohol (261 +/- 138 ml; mean +/- SD) and non-alcohol (174 +/- 61 ml) beer when hypohydrated (P = 0.057), but there was a difference when euhydrated (1279 +/- 256 vs 1121 +/- 148 ml alcohol and non-alcohol, respectively; P < 0.001). Unsurprisingly, more urine was produced on both euhydrated trials than either of the hypohydrated trials (P < 0.001). Blood alcohol concentration was elevated (P < 0.001) 1 h after drinking to 7.1 +/- 1.8 and 6.0 +/- 2.7 mmol/l (hypohydrated and euhydrated, respectively) on the alcohol trials. Serum osmolality was higher 1 h after drinking on both the alcohol trials (303 +/- 5 and 298 +/- 5 mosmol/l) than on their non-alcohol, equivalent hydration trials (290 +/- 8 and 284 +/- 5 mosmol/l hypohydrated and euhydrated, respectively; P < 0.001).

CONCLUSION: These results suggest that the diuretic action of alcohol is blunted when the body is hypohydrated.