Our bodies are made up of up to 60% water. We are advised to drink a certain amount of water every day to prevent dehydration, which can affect the body's ability to perform these functions. But beyond that, what are the benefits to our overall health of drinking water—especially drinking more water?

"For such a ubiquitous, simple intervention, the evidence is unclear and its benefits are not well established, so we need to take a closer look," said Benjamin Breyer, MD, chair of the Department of Urology at the University of California, San Francisco (UCSF) and senior author of the study.

While the optimal amount of water to drink varies from person to person, the National Academy of Medicine recommends a daily fluid intake of about 13 8-fluid ounce cups (3 liters) for men ages 19 to 30, and 9 cups (2.1 liters) for women of the same age.

The researchers systematically reviewed data from previous randomized clinical trials that examined the effects of increasing water intake (except for one study in which water intake was reduced) on health and health-related problems. The studies evaluated different populations, with primary endpoints including weight loss, fasting blood glucose levels, headache, urinary tract infections (UTIs) and kidney stones. Here's what the researchers found.

lose weight

In three studies, overweight and obese adults were randomly assigned to drink 51 ounces (1.5 liters) of water per day. 5 liters) of water for 12 weeks to 12 months, the weight loss was greater compared to the control group: 100%, 87%, and 44%, respectively, compared with the control group. However, in a fourth study involving 38 people, drinking 68 ounces (2 liters) of water per day was not associated with weight change over six months.

fasting blood glucose

In a study of 40 people with recently diagnosed type 2 diabetes (within the past five years), drinking 8 before breakfast showed a significant difference in fasting blood glucose levels (-32.6 mg/dL) compared to a control group (5.3 mg/dL). While fasting blood sugar drops significantly, research isn't clear whether this is due to blood thinning; literally, blood becomes thinner.

Conversely, another study of 60 participants found that drinking 18.6 ounces (550 milliliters) of water within two hours of waking up and 18.6 ounces before bed actually increased fasting blood sugar levels by about 0.6 mg/dL over 12 weeks. Participants in this study were adults who were not receiving diabetes medications and/or lifestyle modifications.

Headache

Two studies evaluated the effects of increasing water intake by 50.7 ounces (1.5 L)/day, with conflicting results. One of the trials, which recruited 102 adults, found that the intervention improved participants' migraine quality of life (MSQL) scores by 4.5 points and reduced the number of days with at least moderate headaches reported; however, these results were not statistically significant.

Another study used the same intervention in adults with migraines or tension-type headaches, but there were no statistically significant effects on MSQL, medication use, number of attacks, average headache intensity, or number of headache hours. However, the study had a small sample size of only 18 participants.

Urinary tract infection (UTI) and overactive bladder

In a randomized trial, 140 premenopausal women with recurrent urethritis who usually drank less than 50.7 ounces (1.5 liters) of water increased their daily water intake. Over a 12-month period, drinking more water per day was associated with a reduced average number of urethritis episodes, fewer antibiotic treatments, and longer time between episodes.

Another study investigated whether increasing water intake would change pathogenic bacteria in the urinary tract. Fourteen premenopausal women who were dehydrated (drinking less than 50.7 ounces per day) increased their daily water intake to 64 ounces (1.9 liters), but there was no difference in bacterial counts between those who drank more water and those who drank no water: 7 percent and 8 percent, respectively. Another study randomly selected 24 adults with overactive bladder, a condition that causes a sudden, uncontrollable urge to urinate, and examined the effects of increasing or decreasing fluid intake on symptoms. Reducing fluid intake by 25% has been associated with less frequent urination, urinary urgency, nocturia, or frequent urination at night.

kidney stones

People who have or are susceptible to kidney stones have long been urged to drink more water to prevent them or to help pass them. Researchers looked at two studies that looked at the relationship between increased water intake and the risk of kidney stones.

There was also a study of 221 patients who, after developing kidney stones for the first time, were either asked to increase their water intake until they urinated 68 ounces (2 liters) per day or did not change their water intake. After five years, the recurrence rate of kidney stones in the intervention group was significantly lower, falling by more than half.

In short, drinking more water has a statistically significant impact on weight loss and kidney stone avoidance. Other single studies showed benefits of drinking more water for headache prevention, uremia, and diabetes control, but did not reach statistical significance.

The researchers say the cost of water is low and the likelihood of adverse effects is extremely low, so more well-designed studies should be encouraged to assess the health benefits proposed in the single study they reviewed.

"The number of rigorous studies is limited, but in some specific areas there are statistically significant benefits," Breyer said. "We know that dehydration can be harmful, especially for people with a history of kidney stones or urinary tract infections. On the other hand, sometimes people with frequent urination may benefit from drinking less water. There is no one-size-fits-all approach to water intake."

The research was published in the journal JAMA Network Open