Caffeine and Dehydration
Felix Weber
2026-03-23
3 min. read
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It is often stated that caffeine acts as a dehydrating agent. It is recommended to limit the consumption of drinks containing this ingredient, as well as emphasizing that caffeine-containing beverages should not be considered a source of hydration. Some even suggest that for every cup of coffee consumed, an additional glass of water should be drunk to compensate for potential fluid losses. However, does caffeine truly have such a dehydrating effect on the body? Does the consumption of coffee actually lead to dehydration of the body?
Advised fluid consumption
Recommendations regarding fluid intake fluctuate between 1.5 and 3 liters daily. The European Food Safety Authority (EFSA) has estimated the daily fluid requirement to be around 2 liters for women and around 2.5 liters for men (at moderate physical activity and moderate environmental conditions). Another frequently employed indicator for calculating the basic fluid requirement is 30 ml/kg body weight, e.g., 70 kg × 30 ml = 2.1 l. When estimating fluid needs, lifestyle, environment (temperature, humidity), type of additional activity, and anthropometric features should be taken into account. It is clear that individuals with a larger body mass necessitate more fluids. It is also crucial to remember that individual needs are not constant and can be augmented due to weather conditions, physical activity, and the number of liquid meals throughout the day. It is estimated that food provides approximately 20–30% of the required fluids.
Caffeine source - A plant-based substance that stimulates
Caffeine is a component derived from plant-based food products, which can be found in coffee, tea, chocolate, cocoa, energy drinks, athlete's gels, and some dietary supplements. The majority of people consume caffeine regularly in the form of coffee. The amount of caffeine in coffee varies greatly and can range from 90 to 250 mg. This depends on the method of preparation and brewing technique. Caffeine is absorbed from the digestive tract and reaches maximum concentration in the bloodstream after 30-120 minutes of consumption, depending on individual body conditions and the presence of food in the stomach. The half-life of caffeine in adults ranges from 3 to 7 hours.
The mode of action of caffeine
The mode of action of caffeine is based on the inhibition of A1 and A2 adenosine receptors, which are located among other places in the heart and the central nervous system (CNS). This results in diverse changes in the human body. One of the main effects is the strong influence on the cerebral cortex, which facilitates cognitive processes, enhances mood, and diminishes fatigue, thereby making it more difficult to fall asleep.
The influence of caffeine on maintaining fluid balance in the body
High intake of caffeine (500 mg) has a diuretic effect, which leads to increased fluid loss. The diuretic effect of caffeine was observed many years ago. The authors of the first publications suggest that caffeine consumption can lead to the development of acute diarrhoea, while regular consumption may lead to the development of tolerance and anti-diuretic effects. Until now, it was thought that a 4-day reduction in caffeine intake could lead to loss of acquired tolerance. In numerous studies evaluating the level of hydration and its relationship with caffeine, different results have been obtained, but the tendency is that higher doses of caffeine in people who do not drink coffee may lead to the development of acute diarrhoea, while lower doses do not show such an effect. In a study conducted by Dr Sophia Killer and her team, the effect of standard doses of caffeine on the hydration level of the body was analysed. The study involved 50 men who drank coffee, and hydration levels were evaluated in several ways. The effect of caffeine consumption was compared with the effect of water. Physical activity, fluid and food intake were controlled. Participants consumed 4 × 200 ml of coffee containing 4 mg of caffeine/kg and the same amount of water. The results showed that there is no difference between regular caffeine consumption and water consumption. Caffeine consumption provides similar water-releasing properties.
