Hyponatremia in the general population. What does it mean?

Hyponatremia is a frequent problem in clinical practice and is known to be associated with a variety of serious adverse outcomes. Estimates from the US general population and several community-based cohorts indicate that hyponatremia is also relatively common in these settings, especially among seniors, individuals with underlying disease, and those taking a variety of prescription medications. Prevalence is greatly increased when persons with a "low normal" level of serum sodium are considered. Population-based studies have identified a U-shaped relationship between serum sodium and all-cause mortality, with the increased risk at the lower end of the distribution being seen in persons with a "low normal" level of serum sodium as well as those meeting the traditional definition of hyponatremia. The hyponatremia associated risk in epidemiologic studies is of lesser magnitude than in hospital-based studies but of great potential importance give the much larger number of persons with a low serum sodium in the general population. An important challenge for the research community is to determine whether low levels of serum sodium are a direct cause of increased risk. Population-based studies are likely to provide the best opportunity to resolve this question.