Findings from the National Institutes of Health suggest that people who don't drink enough fluids may face a higher risk of disease, but some researchers aren't convinced.
Adults who are inadequately hydrated may age faster, face a higher risk of chronic disease and are more likely to die younger than those who are well hydrated, according to a new study from the National Institutes of Health.
The results, which were released Monday, are based on data collected over 25 years from more than 11,000 U.S. adults. Participants attended their first medical check-ups at ages 45 to 66 and then returned for follow-up examinations at ages 70 to 90.
The researchers monitored the participants' blood sodium levels as an indicator of hydration, as higher concentrations are a sign that participants may not have been taking in enough fluids. The researchers found that participants with high blood sodium levels physiologically aged faster than those with lower levels, which was reflected in aging-related health indicators such as high blood pressure, cholesterol and blood sugar levels.
All study participants had blood sodium concentrations considered normal: 135 to 146 millimoles per liter. However, the results showed that people with levels at the higher end of this normal range - above 144 millimoles per litre - were 50% more likely to show signs of physical ageing beyond the expected age compared with those with lower blood sodium levels. They also had an approximately 20% higher risk of premature death.
The study found that even people with blood sodium levels above 142 millimoles per litre had an increased risk of certain chronic diseases, including heart failure, stroke, chronic lung disease, diabetes and dementia.
"The risk of developing these diseases increases with age and the accumulation of damage in various tissues in the body," Natalia Dmitrieva, one of the study's authors and a researcher at the NIH's National Heart, Lung, and Blood Institute, said in an email.
Similarly, Dmitrieva's previous research found that higher blood sodium levels may be a risk factor for heart failure.
Just as regular physical activity and good nutrition are considered part of a healthy lifestyle, she said, "new evidence from our own and other studies suggests that adding consistent good hydration to these healthy lifestyle habits may further slow the aging process."
However, the study authors cautioned that more research is needed to see if good hydration can help slow aging, prevent disease or lead to a longer life.
The relationship between fluid drinking and age-related chronic diseases remains "highly speculative," said Dr. Lawrence Appel, director of the Welch Center for Prevention, Epidemiology and Clinical Research at Johns Hopkins University.
The NIH study "does not prove that drinking more water will prevent chronic disease," he said.
Appel said that people would probably need much higher blood sodium levels (150 millimoles per liter or more, which is the dehydration that can occur during extreme heat) for negative health effects to occur.
He also pointed out that in addition to hydration, many other factors can affect blood sodium levels, such as taking diuretics, also known as water pills, for high blood pressure. Some people with neurological problems or other disabilities may also have higher-than-average blood sodium levels, Dr. Mitchell Rosner, head of the University of Virginia School of Medicine, said in an email.
Dehydration is not a common problem
Hydration has known health benefits. According to the Centers for Disease Control and Prevention, it helps people ward off joint pain and maintain a normal body temperature, and can prevent constipation or kidney stones.
Asher Rosinger, director of the Water, Health and Nutrition Laboratory at Penn State's College of Health and Human Development, said it's more likely that chronic dehydration accelerates the aging process than that good hydration can help slow it down.
Proper hydration "will ensure that the kidneys are working properly and the body is not physiologically burdened with extra weight," he said in an email.
Rosinger added that if a person does not drink enough water and instead consumes sugar-sweetened beverages, the risk of cognitive problems, urinary tract infections, kidney stones and kidney damage increases.
The National Academy of Medicine recommends six to nine 8-dozen cups of fluids a day for women and eight to 12 for men. Dmitrieva said these recommendations are ideal for the average person, and Rosner also felt these guidelines were reasonable. However, both experts noted that people have different hydration needs depending on their activity level and outdoor environment.
Appel, meanwhile, said the traditional recommendation to drink about eight glasses of water a day "really isn't based on any scientific evidence." His research has found that people's normal drinking behavior usually leads to adequate hydration.
"Dehydration in the general population is just not a common problem," he said.
According to the CDC, the average U.S. adult drinks more than five glasses of water a day. Vegetables and fruits with high water content, such as watermelon, celery and cucumbers, can also help with hydration. Dmitrieva said seltzer and unsweetened tea also provide good hydration.
As Rosner said, "water is simply the best, but other beverages are fine in moderation."
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