For Muslims all over the globe, Ramadan is a month-long period of spiritual reflection and purification. During this time, Muslims practice self-discipline by abstaining from food, drink and other physical needs from sunrise to sunset to seek forgiveness and purify their souls. Fasting in the month of Ramadan is one of Islam’s Five Pillars, along with declaration of faith, daily prayer, charity to the poor and making the Hajj pilgrimage in Mecca, Saudi Arabia for those who are able.
Muslims break their fast at sunset, which is known as iftar. The exact time for iftar varies based on location and time of year, but it usually occurs during the Maghrib prayer, one of Islam’s five daily prayers. Muslims break their fast by eating dates and drinking water, just as Prophet Muhammad (peace be upon him) did.
“The thirst is gone, the veins are moistened, and the reward is confirmed, if Allah will.” This is a supplication we make when breaking the fast. As a Muslim living in a city with a hot and humid climate, I can attest that when it’s time to break my fast, water is the only thing on my mind. Drinking water seems to immediately quench my thirst. But does this mean that the water is absorbed from my stomach into the bloodstream at the exact moment of consumption?
The holy month of Ramadan and the great desire to drink water after more than fourteen hours of fasting in a very hot city inspired me to learn about thirst mechanisms and their different stimuli in order to answer this question.
Thirst is a homeostatic response to blood changes. An increase in plasma osmolarity or a decrease in plasma volume or pressure causes thirst, which motivates animals to seek out and consume water, restoring these parameters to their physiological set points.
The thirst center is a group of neurons in the hypothalamus, a part of the brain that regulates bodily processes such as thirst and hunger. The thirst center gets signals from our body’s fluid and electrolyte balance, causing thirst when fluid intake is required. When the body is dehydrated or there is an electrolyte imbalance, the thirst center sends signals to the brain, motivating the person to pursue and ingest fluids. However, it may take 30 to 60 minutes after intake to reabsorb and distribute the water throughout the body.
So, why does thirst seem to vanish as soon as you consume water? Dryness of the mouth and mucous membranes of the esophagus can cause thirst. As a result of simply dampening the mouth and esophagus, even if the water has yet to be absorbed into the bloodstream, a thirsty person may feel immediate relief after drinking it. Another mechanism for immediate thirst quenching is gastrointestinal distension, which can alleviate thirst to some extent as gastrointestinal stimuli influence thirst; for example, simple inflation of a balloon in the stomach can relieve thirst. Mechanical pharyngeal stimulation also plays a role, as drinking water partly alleviates thirst even if there isn’t a surface on the pharynx or esophagus or through which water can get absorbed into the bloodstream. The relief from these mechanisms, however, is fleeting. The sensation of thirst is only completely satisfied when the primary imbalance — either plasma osmolarity or blood volume — reverts to normal. Furthermore, experimental studies have repeatedly demonstrated that animals drink nearly precisely the amount required to restore plasma osmolarity and volume to normal.
In conclusion, drinking water relieves the sensation of thirst immediately, but temporarily, by overcoming the dryness of the mouth and mucous membranes of the esophagus, as well as through the gastrointestinal distension caused by drinking water. The immediate thirst-quenching power of water not only provides immediate satisfaction after a long fast, but plays an essential homeostatic role. If drinking water does not immediately relieve thirst, a person may continue to drink excessively, resulting in overhydration and excessive dilution of bodily fluids.
Guyton, A. C., & Hall, J. E. (2016). Textbook of Medical Physiology (13th ed.). Elsevier.