What makes drinking water so amazingly refreshing and delicious when we’re already thirsty? What makes it different if there is no thirst?
Drinking water stimulates a variety of complex biochemical reactions that reward rehydration and help satisfy our thirst.
Imagine that you are exercising outside on a hot day. You’re drenched in sweat, and the feeling of thirst is starting to get the better of you. You take out your water bottle and take your first big sip, your body instantly filled with relief and exhilaration.
“There’s a savory reaction to it,” Patricia Di Lorenzo, professor emeritus of psychology at Binghampton University in New York, told Live Science. “When you’re really thirsty and you drink water, it tastes very good.”
But, why is drinking water so enjoyable when you’re thirsty?
Blood volume
We feel thirsty when we exercise intensely, because when we sweat, our blood volume decreases. Most areas of the brain are separated by the blood-brain barrier, a layer of cells that prevents harmful toxins and pathogens from infecting the brain.
But certain parts of the brain lie outside this barrier, allowing rapid detection of changes in our blood. When we lose blood volume from exercising or eating salty foods, neurons in these parts of the brain send a signal to stimulate the feeling of thirst.
“This rapid response is very important for survival,” Caltech biology professor Yuki Oka told Live Science. “If it takes too long, you might become dehydrated.”
Three parts of the brain process thirst: the SFO subfornical organ, the organum vasculosum lamina terminalis OVLT, and the median preoptic nucleus. MnPO.
Both the subfornical organ and the terminal lamina vasculature are located outside the blood-brain barrier.
In a 2018 study in mice, Oka discovered that while all three areas contain neurons that drive drinking when these neurons are excited, the intermediate preoptic nucleus is in the middle of this process, relaying thirst signals from the infrafornical organ and terminal lamina vasculature to Other parts of the brain to stimulate drinking.
It takes about 30 minutes after swallowing water for it to be absorbed and distributed throughout your body, Oka says. But your body starts sending signals to your brain that you are well hydrated before you are fully hydrated.
Once you drink the initial sip, your brain releases a rush of the neurotransmitter dopamine. Most scientists agree that dopamine is involved in reward seeking, movement, and motivation. Most importantly, dopamine stimulates the expenditure of energy on actions that give us a reward or help us survive, including eating and drinking.
Dopamine
Oka said that if dopamine is released when animals perform a certain behavior, they “tend to repeat that behavior… This is a positive signal.”
It is still not known exactly how drinking water triggers the release of dopamine. But in a 2019 study published in the journal Neuron, Oka and his colleagues discovered that thirsty mice that drank water released dopamine, while thirsty mice that received water directly into their intestines did not.
This suggests that the act of drinking – not quenching thirst – releases the neurotransmitter. This explains why dehydrated patients who are given intravenous fluids don’t get the same “feeling of reward” they get from drinking a cold glass of water, Oka said.
In a separate process, the act of swallowing also sends a message to neurons in the intermediate preoptic nucleus that the body is receiving water, according to the study. Then the same nucleus turns off the thirst neurons in the subfornical organ, giving a feeling of satiety.
However, swallowing is not the only mechanism that helps stop thirst. After water moves into the intestines, the body detects a decrease in the ratio of salt to water in the blood. This causes levels of a hormone called vasoactive intestinal peptide (VIP) to rise.
This hormone, not the water itself, helps activate neurons that send signals to the brain that the body is satisfied. Much about how this process works is a mystery. Researchers still don’t know where VIP comes from. Or how is it launched?
“We don’t even know how osmolality (the concentration of dissolved particles in the blood) is detected by these intestinal cells,” Oka said, adding, “We are working on that.”
What is thirst?
Thirst is usually just the brain’s way of warning that you’re dehydrated because you’re not drinking enough fluids. But excessive and persistent thirst (known as binge drinking) may be a sign of an underlying problem such as diabetes.
Feeling thirsty all the time and for no good reason is not normal and should be checked by your GP, according to the UK’s National Health Service (NHS).
Common causes of thirst
1- Drought
You usually feel thirsty because you are not drinking enough fluids that your body needs. This may be due to excessive sweating or fluid loss due to diarrhea and vomiting.
You can soon quench your thirst and restore fluid balance in your body by having a drink and making sure you stay well hydrated.
It is especially important to stay well hydrated during hot weather, while exercising, and while you are having vomiting and diarrhea.
2- Food
In some cases, thirst may be triggered by something as simple as a recent meal or snack. Eating salty or spicy foods may suddenly make you thirsty.
3- Diabetes
If you feel thirsty all the time, it may be a sign of diabetes, especially if you also have other symptoms such as needing to urinate frequently, extreme fatigue (fatigue) and unexplained weight loss.
Diabetes is a lifelong condition that makes it difficult to control the level of sugar (glucose) in the blood. High levels of glucose can mean that your kidneys need to produce more urine to help move glucose out of your body. This can make you thirsty because your brain is telling you to drink more to make up for the fluids you’ve lost.
If you feel thirsty all the time and have other symptoms, your GP will likely carry out a blood glucose test to find out if you have diabetes.
4- Pregnancy
Feeling thirsty, as well as urinating more than usual, are common symptoms during pregnancy, and usually nothing to worry about.
In very rare cases, these problems may be a sign of gestational diabetes (a type of diabetes that affects women during pregnancy). You should be screened for this as part of your antenatal care if you are at risk.
5- Medicines
Excessive thirst can sometimes be a side effect of certain types of medications, including lithium, some antipsychotics, and diuretics.
If you think a particular medication is causing your thirst, it may be best to change it to a different medication or reduce your dose. Talk to your GP about this.
Other causes of thirst
There are also many other possible causes of extreme thirst, including:
- Diabetes insipidus, a condition caused by problems with a hormone that regulates the amount of fluid in the body.
- Diabetic ketoacidosis, which is a serious complication of diabetes caused by a lack of the hormone insulin in the body.
- Sickle cell anemia, an inherited blood disorder.
- Psychological binge drinking, where a person with a mental health condition, such as schizophrenia, drinks excessive amounts of water that cannot be eliminated through the kidneys.
- Bleeding.