ABSTRACT

Diuretics are widely prescribed for hypertension and other cardiovascular diseases. They generally work by blocking Na+ reuptake from the filtrate back into the blood. As a result, water follows the loss of Na+, and diuresis results. Loop diuretics block the Na+/K+/2Cl symporter in the thick ascending limb. Thiazide diuretics block a Na+/Cl symporter in the distal convoluted tubule. The potassium-sparing diuretics either block a Na+ channel or antagonize aldosterone in the collecting tubule system. Other diuretics, such as carbonic anhydrase inhibitors and osmotic agents, have limited indications. Diuretics are taken by athletes to drop weight or to mask other illegal substances in their urine. Their use can decrease plasma volume and impair normal vasodilatory response to exercise. Hypovolemia initiates cardiovascular adjustments to preserve blood pressure (i.e., maintain venous return and cardiac output), at the expense of regulation of body temperature. Hypovolemia causes changes in circulation, decreasing the ability to thermoregulate, by both evaporative cooling (i.e., sweat) and cooling by radiation. Although hypovolemic exercisers still sweat, creating an even more negative water balance, their sweat rate and the related cooling effect can be reduced. This problem can be exacerbated in warm, humid weather, leading to heat exhaustion.

Exercise causes shifts in electrolyte distribution, and diuretics can exacerbate their loss. K+ loss with diuretics leads to earlier muscle fatigue and may affect the heart during intense exercise. Salt loss can result in an increased chance of muscle cramps and/or cardiac arrhythmias. Performance can be suppressed after rapid dehydration and rehydration, and decreased duration/stamina would be expected. Athletes and exercise enthusiasts who are taking diuretics other than potassium-sparing drugs should eat fruit such as bananas or drink sport drinks with electrolytes to help alleviate salt and water imbalance and prevent hypokalemia. Thiazide diuretics (and related sulfonamides) can cause photosensitivity, so individuals taking these drugs should use sunscreen and avoid the sun during midday hours.