We're regularly told to drink plenty of water to maintain our health. A new study provides a few more good reasons to stay well-hydrated – including fewer chronic health conditions and a greater chance of living a longer life.

This is based on research involving 11,255 adults who were questioned five times across the course of 25 years on factors such as socieconomic status and family medical history.

Clinical testing on the volunteers provided measures of sodium in their blood serum, which was used as an indicator of their fluid intake. Usually, the more water we drink, the lower the level of sodium in our bloodstream.

"The results suggest that proper hydration may slow down aging and prolong a disease-free life," says research scientist Natalia Dmitrieva, from the National Heart Lung and Blood Institute (NHLBI) in Maryland.

Previous research has highlighted a link between higher sodium levels in the blood and an increased risk of heart failure. The normal range of sodium levels in a person's blood usually falls between 125 to 146 milliequivalents per liter (mEq/L). In the study, serum samples with higher sodium levels were also more likely to contain elevated levels of up to 15 different markers of biological health and aging.

For example, those with sodium levels above 142 mEq/L had a 10 to 15 percent associated increased odds of being biologically older than their chronological age, when compared to those showing more typical ranges. There was also a 64 percent greater associated risk for developing chronic diseases including heart failure, stroke, atrial fibrillation, chronic lung disease, diabetes, and dementia.

The study authors suggest that measuring levels of sodium in the blood could inform advice from doctors. Those people who are in the danger zone as far as fluid intake is concerned could take steps to get more water into their system – not just from drinking it but also through juices, vegetables, and fruits.

"The goal is to ensure patients are taking in enough fluids, while assessing factors, like medications, that may lead to fluid loss," says senior investigator Manfred Boehm, from the NHLBI.

"Doctors may also need to defer to a patient's current treatment plan, such as limiting fluid intake for heart failure."

The researchers emphasize that their method can't prove that the volunteer's hydration is what is primarily responsible for boosting their odds of having good health. Randomized, controlled trials are more suitable for that, though we can already see an association worth investigating further.

Fluid intake isn't the only factor that affects sodium levels in the blood either, though the researchers did control for variables including age, race, and biological sex, as well as excluding study participants with conditions such as diabetes or habits such as smoking that could affect their levels of sodium.

It's also worth pointing out that this study concentrates more on the health risks of dehydration, rather on additional positive effects of being well hydrated – although the two are of course going to be linked to some extent.

At the moment, about half of the world's population don't get as far as the recommended daily intake (which typically starts at around 1.5 liters a day). There are a variety of reasons for that, not least access to clean, potable water. Ensuring all communities have a clean drinking supply close at hand ought to priority number one for keeping everybody health.

For those who have plenty of options, getting that fraction higher could make a significant difference to disease and mortality risk.

"On the global level, this can have a big impact," says Dmitrieva. "Decreased body water content is the most common factor that increases serum sodium, which is why the results suggest that staying well hydrated may slow down the aging process and prevent or delay chronic disease."

The research has been published in eBioMedicine.