According to findings from the Osteoporotic Fractures in Men (MrOS) study, low serum sodium concentrations are associated with cognitive impairment and cognitive decline in older community-dwelling men. The findings were published in the Clinical Journal of the American Society of Nephrology.

The results support recent evidence that mild declines in serum sodium, which would likely be unnoticed in clinical practice, are unlikely to be asymptomatic. Mild hyponatremia is common in older adults and was once thought to be asymptomatic, but recent studies have linked it to attention deficits, gait disturbances, fracture risk, cardiovascular events, and mortality.

Researchers used data from 5,435 men (mean age, 74) who participated in the MrOS study to investigate possible associations between hyponatremia and cognitive impairment and decline. The lowest tertile of serum sodium (126-140 mmol/L) was associated with a significantly increased risk of prevalent cognitive impairment in both adjusted and unadjusted analyses, as was lower serum sodium in continuous analyses.

The lowest tertile of serum sodium also was associated with a significantly increased risk of cognitive decline, as was the highest tertile of serum sodium (143-153 mmol/L). Tertile 2 (141-142 mmol/L) was the reference group. Clinical hyponatremia (serum sodium <136 mmol/L) was associated with 2.35-fold increased odds of cognitive impairment at baseline. Clinical hyponatremia was not, however, significantly associated with cognitive decline.

A caveat is that only 52 individuals were hyponatremic at baseline in this analysis. Slightly lower serum sodium levels are associated with both prevalent cognitive impairment as well as cognitive decline in older men. Whether correction of serum sodium levels improves cognitive function requires further research. This research question should be examined further in older women, as prior studies in severe acute hyponatremia suggest women are at higher risk of neurologic consequences.

There is a major flaw in the study, which was pointed out by the authors: there was only one sodium level drawn. It is not known how long patients were hyponatremic or were they hyponatremic at follow-up testing. These are very important questions, and the researchers not sure what they can draw conclusively from this study with this limitation. Nevertheless, he recommends that physicians address mild hyponatremia. Evaluate for potential reversible factors (excess fluid in heart failure patients, medications, diet, etc.).

The research team is not sure if hyponatremia is an independent risk factor or just a marker. There are no data that treating and reversing mild hyponatremia will improve cognitive function.