Investigation and comparison of the effect of consuming different doses of coffee on fluid balance, electrolytes and VO2max of active men

 Today, the consumption of caffeinated beverages such as coffee has increased among athletes. The aim of this study was to investigate and compare the effect of consuming two different doses of coffee on fluid balance, electrolytes and VO2max in active men.

In quasi-experimental studies, 54 trained men (Age: 20.89±1.31 y; Weight: 70.10±8.43 kg; Height: 174.7±5.65 cm; VO2max: 52.16±5.99 ml/kg/min) were randomly selected and  divided  into three equal groups (N=18). All subjects consumed equal amounts of 3 cups of coffee per day for 5 days (balancing stage), on the sixth and seventh day (test stage) subjects of three groups consumed 0, 3 and 8 cups of coffee per day (equivalent to 0, 258 and 688 mg caffeine per day, respectively). with no other dietary caffeine intake, for 7 days. Before and after the intervention, subjects 'body weight was measured, blood samples were taken to examine blood factors, and subjects' VO2max was assessed using the Fox protocol. The measuring of indices changes in subject's body fluids, electrolytes and VO2max in 3 levels of controlled coffee ingesting, were analyzed by multivariate test (MANOVA) and Tukey post hoc in (P≤0.05).

Percent plasma volume changes in ingestion level of 0 (cup / day) was increased significantly (P = 0.013), compared to ingestion level of 3 (cup / day). The mean body weight of subjects at the ingestion level of 0 (cup / day) showed a significant increase (P = 0.001), compared to the other two levels. Concentration of the serum sodium at the ingestion level of 3 (cup / day) showed a significant increase (P≤0.05), compared to the other two levels. There was no changes in the concentration of serum potassium between different levels of caffeine ingestion. Estimated VO2max in the two forms of absolute and relative at the ingestion level of 8 (cup / day), showed a significant decrease (P= 0.003) compared to the other two levels .

Consumption of coffee in different doses reduces body fluids, increases serum sodium concentration and possibly increases sodium excretion and decreases VO2max in active people. Accordingly, considering the importance of maintaining body fluids on the performance of athletes, it seems that coaches and sports professionals have the necessary care in the amount or time of consumption of this drink.