Do Coffee, Tea, and Beer Truly Have Dehydrating Properties?

The body maintains a constant level of water loss, while fluid intake occurs intermittently. Normally, the mechanisms responsible for homeostasis maintain hydration at a constant level, so severe fluid deficits are a rare phenomenon among the majority of the population. Standard imbalances in water balance usually return to normal after 24 hours. The European Food Safety Authority has estimated the daily requirement for fluids, i.e., the sum of the water volume from beverages and food, to be around 2 l for women and around 2.5 l for men (at moderate physical activity and moderate environmental conditions). This corresponds to 30–45 ml/kg body weight, e.g., 70 kg × 30 ml = 2100.

Several factors, such as the frequency of fluid consumption, volume, and composition, influence the body's hydration level. The components of different fluids are metabolized and excreted at various time intervals, affecting gastric emptying and the rate of their absorption in the intestine. Upon reviewing analyses, we can find studies comparing the effectiveness of hydration in the context of accelerated regeneration in physically active individuals. In 2016, Prof. Ron Maughan and his team analyzed various fluids available on the market and identified those with the highest hydration efficiency and supporting long-term maintenance of fluid balance. Several beverages with better hydrating properties than water were highlighted, including oral rehydration solutions, skim milk, whole milk, and orange juice. These beverages have significantly more calories and nutrients, which can slow gastric emptying but also lead to greater fluid retention. A surprising fact is that beer, tea, and coffee achieved results very comparable to water, suggesting they do not have dehydrating properties, as often heard.

Selecting the appropriate amount of fluids is a highly personal matter. Organizations and scientific societies establish certain guidelines regarding the fluids we consume. By observing our body, we can choose the appropriate quantity of fluids tailored to our unique needs. Nevertheless, it is essential to bear in mind that water should be the primary source of hydration, despite the fact that other fluids with equally good or even superior hydrating properties have been highlighted.