Eight Glasses of Water a Day: The Myth and the Reality

According to Aaron E. Carroll, MD, “There is one health myth that will not die: you should drink eight glasses of water a day.”

In his article for the New York Times, published August 24, 2015, Dr. Carroll, a professor of pediatrics at Indiana University School of Medicine, explains that while there is no science behind it, the myth continues.

“Many people believe that the source of this myth was a 1945 Food and Nutrition Board recommendation that said people need about 2.5 liters of water a day,” writes Dr. Carroll. “But they ignored the sentence that followed closely behind. It read, ‘Most of this quantity is contained in prepared foods.’”

“Water is present in fruits and vegetables. It’s in juice, it’s in beer and it’s even in tea and coffee. Before anyone writes to tell me that coffee is going to dehydrate you, research shows that’s not true either.”

Although Dr. Carroll recommends water as the best beverage to consume. He also emphasizes that it is not the only source for hydration. “You don’t have to consume all the water you need through drinks,” says Dr. Carroll. “You also don’t need to worry so much about never feeling thirsty. The human body is finely tuned to signal you to drink long before you are actually dehydrated.”

Variables for hydration requirements

Although there is no formal recommendation for the daily amount of water people need, the amount differs depending on where a person lives, what foods they eat, their size, level of activity and other factors, such as disease.

‘Most desert dwellers are well aware of the risks of dehydration,” says Cardiologist Khoi Le, MD, Board Certified in Internal Medicine and Cardiac Electrophysiology. “However, drinking too much water can also cause problems.”

Drinking too much water can lead to electrolyte imbalance, especially in the elderly, or long distance runners who may overconsume water following a race.

“Overhydration, also known as water intoxication, results in excessive dilution of important electrolytes and especially of sodium,” explains Dr. Le. “This can occur when water intake exceeds the ability of the kidneys to regulate the amount and balance of water and electrolytes in the body. In most healthy adults, this is quite rare because the kidneys are so efficient. However, medical conditions including congestive heart failure, liver disease, kidney disease and diabetes can be associated with water retention.”

Medications and Hydration

“Medications such as diuretics, nonsteroidal anti-inflammatory drugs, and antipsychotics affect how the kidneys handle fluid and electrolytes and raise the risk for hyponatremia (sodium dilution),” says Dr. Le.”

On the other hand, older people may be vulnerable to dehydration which can be complicated by disease states and physical frailty. Dehydration can be more common in people with cognitive impairment and changes in functional ability.

One sign of normal hydration shows up in the bathroom — urinating every two to four hours with urine that stays light yellow means good hydration.

Water is the best beverage to consume as part of a healthy diet. But remember that an equally healthy diet that includes plenty of fresh fruits and vegetables contributes to one’s daily intake of fluids. When in doubt about how much water to consume, check with your physician for guidelines.

“I agree with Dr. Caroll that the old adage to drink eight glasses of water every day should be put to rest,” says Dr. Le. “There is no set amount that is right for every person, every day. In general, I recommend to my patients to use thirst and the color of the urine as a guide.”