Adults who stay well-hydrated appear to live longer and develop fewer chronic conditions, a study suggests.

The peer-reviewed findings of the National Institutes of Health (NIH), a US medical research agency, were published in the eBioMedicine journal on Monday.

Using health data gathered from 11,255 adults over 30 years, researchers analysed links between serum sodium levels – which go up when fluid intake goes down – and various indicators of health.

They found adults with serum sodium levels at the higher end of a normal range were more likely to develop chronic conditions and show signs of advanced biological ageing than those with levels in the medium ranges.

Adults with higher levels were also more likely to die younger, they said.

“The results suggest that proper hydration may slow down ageing and prolong a disease-free life,” said Natalia Dmitrieva, study author and researcher at the Laboratory of Cardiovascular Regenerative Medicine at the National Heart, Lung and Blood Institute (NHLBI), part of NIH.

In March, the scientists published a study which found links between higher ranges of normal serum sodium levels and increased risk of heart failure.

For the new study, researchers assessed information participants shared during five medical visits – the first two when they were in their 50s and the last when they were between 70 and 90.

They excluded adults who had high levels of serum sodium at baseline check-ins or with underlying conditions, like obesity, which could affect serum sodium levels.

They then evaluated how serum sodium levels correlated with biological ageing, which was assessed through 15 health markers.

They included factors such as systolic blood pressure, cholesterol and blood sugar, which provided insight about how well each person’s cardiovascular, respiratory, metabolic, renal and immune system was functioning.

They also adjusted for factors like age, race, biological sex, smoking status and hypertension.

They found adults with higher levels of normal serum sodium – with normal ranges falling between 135-146 milliequivalents per litre (mEq/L) – were more likely to show signs of faster biological ageing.

This was based on indictors like metabolic and cardiovascular health, lung function and inflammation, they said.

Adults with serum sodium levels above 142 mEq/L had up to a 64% increased associated risk for developing chronic diseases like heart failure, stroke, atrial fibrillation and peripheral artery disease, as well as chronic lung disease, diabetes and dementia, they added.

But adults with serum sodium levels between 138-140 mEq/L had the lowest risk of developing chronic disease, they said.

The researchers said the findings do not prove a causal effect.

They said randomised, controlled trials are needed to see if optimal hydration can promote healthy ageing, prevent disease and lead to a longer life.