Thirst: or, why do people drink?

Abstract

Summary Over half the human body is water, which is essential for the correct functioning of virtually all living cells. The body has developed mechanisms to maintain water balance under conditions of mildly fluctuating availability and generally, consumption of 1.5 L of liquid per day is sufficient, in conjunction with the liquid ingested as a component of food, to replace the water lost throughout the day. However, the mechanisms do not trigger the sensation of needing to drink until there is already a water deficit. In normal circumstances in temperate climates this does not matter, but athletes, the young, the elderly and those working in hot climates have to take special steps to ensure they drink regularly and before they feel thirsty. As with all food, variety is good because the drinks supply other useful components of the diet in addition to water. While the rate of rehydration is rarely important in temperate climates, in circumstances where it does matter, such as in some illnesses, the addition of carbohydrate and salt has been shown to improve the rate of transfer of water from the gut into the body.