Objective: To assess the effect of exercise on water turnover in endurance trained middle aged men.
Methods: Water turnover was assessed using 2H2O as a tracer for water in six exercising and six sedentary middle aged men over seven consecutive days. The exercising subjects ran on average 14.8 km per day, while the sedentary group did not take part in any regular physical activity.
Results: The average median (range) rate of water turnover (ml.d-1) was higher in the exercising group [4673 (4320 to 9606)] than in the sedentary group [3256 (2055 to 4185); P = 0.001]. Although there was a tendency for non-renal water losses (ml.d-1) to be greater in the exercising group [1746 (1241 to 5196)] than in the sedentary group [1223 (1021 to 1950); P = 0.08], the major difference in water loss between the groups was the greater urine output (ml.d-1) in those who exercised [3021 (2484 to 4225)] compared to those who were sedentary [(1883 (925 to 2266); P = 0.001].
Conclusions: The results suggest that fluid intake in middle aged men who exercise regularly must be greater than that of sedentary individuals of the same age group, and that the difference in volume is in excess of that required to replace exercise induced sweat and respiratory water losses.