BackgroundHyponatremia is frequent in older age; whether it is a key player, a surrogate marker, or an innocent bystander in age-related diseases is still unclear.Objective: To understand
the role of hyponatremia in falls, osteoporosis, fractures, and cognitive
impairment in old patients.MethodEligibility criteria for study inclusions were: written in English, peer-reviewed observational and intervention studies, clinical trial, prospective and retrospective controlled cohort studies, and case-controlled studies without limitations regarding the date of publication.Information sources: Protocol available on the International Prospective Register of Systematic Reviews (PROSPERO, CRD42021218389). MEDLINE, Embase, and PsycINFO were searched. Final search done on August 8, 2021.Risk-of-bias assessment: Risk-of-Bias Assessment tool for Non-randomized Studies (RoBANS) and the Bradford Hill’s criteria for causality.ResultsIncludes studies: One-hundred thirty-five articles retained for the revision.Synthesis of results—Falls: Eleven studies were included. Strong association between hyponatremia and falls in all the studies was found.Osteoporosis and fractures: nineteen articles were included. The association between hyponatremia and osteoporosis is unclear.Cognitive impairment: Five articles were included. No association between hyponatremia and cognitive impairment was found.DiscussionInterpretation: Falls, osteoporosis, and fractures are multifactorial. Hyponatremia is not temporally related with the outcomes; we suggest that hyponatremia may be regarded as a marker of unhealthy aging and a confounder instead of a causal factor or an innocent bystander for falls and fractures. Concerning cognitive impairment, there are no evidence supporting a real role of hyponatremia to be regarded as an innocent bystander in neurodegeneration.