While it is clear that humans cannot survive for longer than several days without water, very little research has assessed how average individuals' health is affected by drinking extra fluids. Experts have claimed that ingesting water is helpful for everything from clearing toxins and keeping organs healthy to warding off weight gain and improving skin tone.
To investigate the true benefits of drinking water, Dan Negoianu, MD, and Stanley Goldfarb, MD, of the Renal, Electrolyte, and Hypertension Division at the University of Pennsylvania, in Philadelphia, PA, reviewed the published clinical studies on the topic. They found solid evidence that individuals in hot, dry climates, as well as athletes, have an increased need for water. In addition, people with certain diseases benefit from increased fluid intake. But no such data exist for average, healthy individuals. In addition, no single study indicates that people need to drink the recommended "8x8" amount of water each day. Indeed, it is unclear where this recommendation came from.
This scan of the literature included a look at studies related to the notion that increased water intake improves kidney function and helps to clear toxins. A variety of studies reveal that drinking water does have an impact on clearance of various substances by the kidney, including sodium and urea. However, these studies do not indicate any sort of clinical benefit that might result.
Other studies have tested water's effects on the functioning of organs. They indicate that water retention in the body is variable and depends on the speed with which water is ingested-if it is gulped quickly, water is more likely to be excreted, while if it is sipped slowly, it is retained in the body. However, no studies have documented any sort of benefit to organs based on increased water intake, regardless of speed.
Drs. Negoianu and Goldfarb also investigated the theory that drinking more water will make people feel full and curb their appetite. Proponents say this may help people maintain their weight and even help fight obesity. But studies remain inconclusive. No carefully designed clinical trials have measured the effects of water intake on weight maintenance.
Headaches also are often attributed to water deprivation, but there are few data to back this up. Only one small trial has addressed the question, and while trial participants who increased their water intake experienced fewer headaches than those who did not, the results were not statistically significant.
In addition, water has been touted as an elixir for improved skin tone. While dehydration can decrease skin turgor, no studies have shown any clinical benefit to skin tone as a result of increased water intake.
The literature review by Drs. Negoianu and Goldfarb reveals that there is no clear evidence of benefit to increasing water intake. On the other hand, no clear evidence exists of a lack of benefit. "There is simply a lack of evidence in general," they explain.