People who drink less than a couple of glasses of water each day may be more likely to develop abnormally high blood sugar, a new study suggests.
When someone's blood sugar levels are high, but not high enough to fit the definition of diabetes, doctors often consider that person to have "pre-diabetes" -- which puts them at risk of developing the disease itself.
In the new study, adults who drank only half a liter of water -- about two glasses -- or less each day were more likely to develop blood sugar levels in the pre-diabetes range, versus people who drank more water.
But whether simply drinking water will cut your risk of blood sugar problems is still up in the air.
The findings show a correlation between water intake and blood sugar, but do not prove cause-and-effect, said senior researcher Lise Bankir, of the French national research institute INSERM.
Still, it is plausible based on biology, Bankir told Reuters Health in an email.
A hormone called vasopressin is the potential missing link, according to the researchers.
Vasopressin -- also known as antidiuretic hormone -- helps regulate the body's water retention. When we are dehydrated, vasopressin levels go up, causing the kidneys to conserve water. But research suggests that higher vasopressin levels may also elevate blood sugar.
There are vasopressin receptors in the liver, the organ responsible for producing glucose (sugar) in the body, Bankir explained. And one study found that injecting healthy people with vasopressin caused a temporary spike in blood sugar.
"There are good arguments to suggest that there could be a real cause-and-effect relationship in the association we have found," Bankir said, "but this is not a proof."
The findings are based on 3,615 French adults who were between the ages of 30 and 65, and had normal blood sugar levels at the outset. About 19 percent said they drank less than half a liter (17 ounces) of water each day, while the rest drank up to a liter or more.
Over the next nine years, 565 study participants developed abnormally high blood sugar and 202 developed type 2 diabetes.
When the researchers looked at the participants' risk according to water intake, they found that people who drank at least 17 ounces of water per day were 28 percent less likely to develop high blood sugar than those who drank less than that amount.
There was no strong statistical link between water intake and risk of developing diabetes, however.
One obvious explanation for the connection with high blood sugar would be that people who drink little water may instead be reaching for sugary drinks -- which could lead to weight gain and impaired blood sugar control.
But Bankir and her colleagues accounted for sugary drinks and alcohol, as well as people's body weight at the start of the study, their reported exercise levels and certain other health factors. And the link between low water intake and high blood sugar persisted.
However, they could not account for everything, including generally healthy or less-healthy eating habits.
"Healthier behaviors correlating with higher water drinking could account for the observed association," the researchers write.
As for why there was no link between water intake and diabetes itself, Bankir said that the number of diabetes cases in the study was "too small to get a significant result." A larger study might have been able to detect a statistically significant link, she noted.
Further studies are needed to confirm the findings on blood sugar, according to Bankir.
But for now, she said, replacing sugary, high-calorie drinks with water would be a good idea for anyone.
"In Western countries, the consumption of sugar is surely too high and contributes to obesity," Bankir said.
"Drinking less of them (sugary drinks) and more pure water can only be good in my view," she said.