Question

What is the pathophysiology behind the belief that caffeine has a diuretic effect when consumed and will induce dehydration if used by athletes or those who perform strenuous exercise.

Answer 1

Caffeine exerted a minor diuretic effect which was negated by exercise. Concerns regarding unwanted fluid loss associated with caffeine consumption are unwarranted particularly when ingestion precedes exercise.

The underlining mechanism of caffeine induced diuresis is not yet clear. It has been postulated, methylxanthines such as caffeine can inhibit phosphodiesterases in the proximal tubule of the kidneys, which may contribute to the diuretic effect. Antagonism of adenosine receptors may also mediate caffeine induced diuresis and natriuresis.Because caffeine does not increase the kidneys' glomerular filtration rate, the diuretic effect is more likely to be related to its natriuretic effect following adenosine receptor blockade. Evidence shows that caffeine acts on the kidneys by inhibiting sodium reabsorption in the proximal and distal tubules, thus increases the solute excretion and consequently free water excretion.

Concerns about fluid deficit associated with caffeine ingestion is highly relevant to sports, health and fitness, industry, and military, where exercise is often accompanied with caffeine ingestion. Caffeine is commonly used as an ergogenic aid in ultra-endurance and multi-day sports events. Likewise, coffee and energy drinks are popular beverages for health and fitness, the military, as well as for workplace productivity. Whether performing prolonged labor or exercising in hot climates with limited access to fluid replacement, hydration is a challenging issue. Consuming caffeine potentially increases the risks of fluid deficits for athletes, fitness enthusiasts, industrial workers, and military personnel if a diuretic effect exists.