Hyponatremia, defined as a serum sodium level below 135 mmol/L, is the most widespread electrolyte disorder in both hospitalized and outpatients [1], [2] and has been widely associated with adverse patient outcomes [3], [4], [5], [6]. Among them, there is a growing body of evidence about the possible association between hyponatremia, falls and fractures, and osteoporosis.

The first clinical study investigating the possible association between hyponatremia and falls and fractures was conducted in 2008 by Kengne and colleagues [7]. In their analysis, the authors showed an adjusted odds ratio (OR) for bone fracture associated with hyponatremia of 4.16, with a 95 % confidence interval (CI) between 2.24 and 7.71.

Since 2008, multiple studies have consistently demonstrated that hyponatremia is associated not only with an increased risk of falls and fractures, but also constitutes an independent risk factor for reduced bone mineral density (BMD) and osteoporosis *[8], [9]. These findings have been subsequently summarized in numerous reviews and meta-analyses [10], [11], [12], [13], [14]. Of note, to date only one study has specifically investigated the potential association between hyponatremia and trabecular bone score (TBS), a non-invasive index widely used in clinical practice to assess bone microarchitecture. In their study, Bioletto et al. [15] performed a cross-sectional analysis of 4204 individuals aged 50 years or older from the 2005–2008 NHANES cycles. While the authors confirmed the association between mild hyponatremia and lower BMD T-score at the total hip as compared to normonatremia (p = 0.03), no association was found with lower TBS (p = 0.81).

However, despite the growing body of evidence of an association between hyponatremia and falls, fractures and osteoporosis, a comprehensive review of the possible pathophysiology of this association is still lacking. This narrative review aims to address this gap by summarizing the current evidence on the pathological impact of hyponatremia on bone, beginning with findings from preclinical studies and subsequently presenting available clinical research in humans.