People have been arguing for decades about how much water you should drink every day. It seems like a simple question, but the answer is complicated. Many people believe that everyone needs to drink eight 8-ounce glasses of water daily. That’s about two liters. Perhaps, some people figure, ten glasses would be even better. Is there any science to support this dogma?
Study Fails to Support Eight Glasses of Water for Everyone:
Advocates who believe that we should all drink more water may get quite emotional at the suggestion we might need less.
Nevertheless, that was the conclusion from a recent study published in the journal Science (Nov. 24, 2022). The researchers point out that water intake need depends on water turnover. To determine this, the scientists measured water turnover by having 5,604 participants drink heavy water. That is water containing deuterium, an isotope of hydrogen with twice the mass of ordinary hydrogen. It is stable, safe and can be readily tracked. The researchers utilized that marker to determine how much water people’s bodies were actually using.
Water turnover was highest among young men, ages 20 to 30. For women, water turnover was relatively unchanged from age 25 to 60, but pregnancy and breast-feeding increased it. People in hot, humid environments and those at high altitude had higher levels of water turnover. They might need more than eight glasses of water daily. Athletes had higher water turnover than couch potatoes, and people who do manual labor outdoors use more water than those working indoors at a desk. All of these factors affect the amount of water an individual needs. Generally, older people need less water than adults between 20 and 40 years old.
Fluid in Foods:
One factor not taken into account by the conventional estimate of eight 8-ounce glasses a day was the amount of liquid consumed in food. People who eat a lot of soup or drink smoothies for breakfast may get a significant amount of fluid in their food. However, this is actually quite difficult to measure scientifically, and the authors of this study state that no research addresses it adequately.
The body has a very sophisticated system for regulating fluid and electrolytes. In general, when people need more liquid, the brain sends a signal that says: Thirsty! Drink! In most situations, that works surprisingly well. However, there are times when thirst is not adequate to keep us properly hydrated.
Urinary Tract Infections:
One woman wrote us that drinking more water may reduce the frequency of urinary tract infections (British Journal of General Practice, March 2020). When she experimented with this approach, she found it helpful.
“I have personally had fewer UTI’s in the past year since I increased my intake to at least 8 glasses of water and started taking 1 g of d-mannose three times a day.”
Who would ever imagine that drinking water could be controversial? Yet discussions of how much water you should drink every day–or even what type of water is best–can get quite contentious. Becoming dehydrated is dangerous, of course, but should you worry that you might over hydrate?
Too Much Water Can Be Dangerous, Too:
One reader observed:
“When I was very ill with long COVID and Lyme disease, I drank too much water. I ended up with my blood too dilute and was hospitalized with syndrome of inappropriate anti-diuretic hormone (SIADH). I stopped eating and urinating and gained 15 pounds of water over about a week. The hospitalization was necessary to restore the sodium concentration in my blood so I could urinate again and live.”
SIADH is a dangerous condition that may be triggered by infection, certain cancers and some medications. The low sodium levels (hyponatremia) that result from this disorder can be life-threatening.
Occasionally, a person may develop hyponatremia simply from taking in more water than the body can process. Sometimes athletes striving to avoid dehydration during a lengthy event overshoot and drink too much water. The symptoms may include weakness, dizziness, nausea, headache and lethargy.
Can You Over Hydrate by Drinking Too Much?
Q. Is it possible to over hydrate? When I was growing up, no one carried a bottle of water around. Now it seems as if everyone is constantly sipping bottled water throughout the day.
One friend believes that if she doesn’t drink at least 8 to 10 glasses of water daily she is jeopardizing her health. Couldn’t consuming too much water lead to dangerously low sodium levels by dilution?
Dangers of Drinking Too Much Water:
A. People used to drink when they were thirsty, and that is still a good idea. These days, though, there is a widespread belief that the more water we drink the healthier we will be. Unless someone has had a kidney stone, there is no evidence that extra fluid consumption throughout the day is beneficial. If the kidneys are working properly, medical guidelines suggest that thirst is a good indicator for when you need to drink. One exception: the elderly, whose kidneys and thirst mechanisms may not be in sync, might need to pay attention to getting adequate fluids.
People who are sweating heavily, such as marathon runners in hot weather, may be thirsty enough to drink a lot of water. They need to be careful to replace electrolytes as well, since over hydration with plain water can lead to sodium depletion (hyponatremia).
According to the online healthcare resource UpToDate,
“The majority of athletes who develop hyponatremia are asymptomatic or mildly symptomatic (eg, weakness, dizziness, headache, lethargy, nausea/vomiting). However, severe manifestations can occur, including seizures, cerebral edema, noncardiogenic pulmonary edema, and death.”
It is important to keep remember that both too little water intake and too much can be a problem.
One reader noted:
“I have been told that if you wait until you are thirsty, you have waited too long and are already dehydrated. If I just listen to my body and drink when I am thirsty, I don’t need to measure how much I drink.”
Most people can let thirst be their guide on how much to drink. Older people and those who are ill, however, may not be able to rely on thirst. In addition, people exercising outdoors, especially in hot climates, may need to pay close attention to getting the water they really need.
Sometimes people hear that beverages such as coffee, tea or juice “don’t count.” As a result, they conclude that they need to drink water above and beyond their intake of other beverages. We are assured that all the liquids you drink, even those you eat in foods, get used by the body to satisfy its fluid requirements. As a result, most people during a normal day don’t really need to force themselves to drink more water.