Longevity briefs provides a short summary of novel research in biology, medicine, or biotechnology that caught the attention of our researchers in Oxford, due to its potential to improve our health, wellbeing, and longevity.
Why is this research important:
When it comes to longevity, the simplest of interventions can sometimes be the most impactful. There may one day be a pill that can make you younger, but until then we need simple practices we can adopt now in order to slow down the rate of ageing. Recently, a study grabbed the attention of many media outlets when it suggested that simply remaining hydrated throughout the day might slow biological ageing. What exactly did the authors of this study do, and what were their findings?
What did the researchers do:
In the study, researchers looked at data from an existing follow-up study called ARIC. The study enrolled 45–66 year-old men and women from four U.S communities and followed them up with 5 clinical examinations which took place over about 35 years. The researchers looked at the blood sodium concentrations in 11 255 participants for whom this data was available. Blood sodium is closely related to the body’s water balance, with higher water intake resulting in lower blood sodium concentrations and vice versa. The researchers omitted anyone with a blood sodium level outside of the normal range in order to exclude anyone with medical abnormalities affecting water balance. Participants also fasted 12 hours before the examinations, so their blood sodium concentrations shouldn’t have been affected by recent salt intake.
Researchers then calculated participants’ biological age, which is a way of estimating how well someone’s tissues and organs operate relative to the population average. For example, if you have a biological age of 30, you are about as healthy as the average 30 year-old. In this study, researchers calculated biological age based on 15 markers of cardiovascular health, kidney performance, respiratory health, metabolic health and immune system function. The researchers then looked to see if there was a relationship between blood sodium concentration and biological age, risk of chronic disease, and mortality after controlling for confounding factors like sex, race and smoking status.
Key takeaway(s) from this research:
The researchers took 135–146 mmol/l as the range for normal blood sodium concentration. After adjusting for confounders, those with a sodium concentration of 137–142 mmol/l had the lowest risk of death from all causes. By comparison, those with the highest sodium levels (144.5–146 mmol/l) had a 21% increase in all cause mortality, while those in the lowest range (135–136.5 mmol/l) showed a 71% increase in mortality.
Higher (but not lower) blood sodium concentrations were also associated with increased biological age. Odds of being biologically older than one’s chronological age were 50% greater in those with serum sodium exceeding 144 mmol/l as compared to participants with serum sodium 137–142 mmol/l. Both greater biological age and increased sodium concentration were also associated with increased risk of chronic disease. A sodium concentration of 138–140 mmol/l was associated with the lowest risk of developing chronic diseases. Higher serum sodium was associated with up to 63% increased odds to develop chronic diseases, while lower serum sodium was associated with an increased risk of up to 36%.
So, sodium concentrations at both the high end and the low end of the normal range appear to be linked to increased risk of chronic disease and death, though only high sodium predicted an increased rate of biological ageing. The authors assumed that changes in blood sodium were primarily due to hydration habits of the participants. However, they note that the lower sodium levels were less likely to be due to overhydration, and more likely to be the result of undiagnosed disease. Underhydration on the other hand is a primary cause of elevated sodium, with an estimated 50% of people worldwide drinking less than the recommended quantity of fluids. However, since this was an observational study, it doesn’t prove cause and effect. We still need randomised trials to know for certain whether optimal hydration reduces mortality and disease.
Middle-age high normal serum sodium as a risk factor for accelerated biological aging, chronic diseases, and premature mortality: https://doi.org/10.1016/j.ebiom.2022.104404