Background: Serum sodium abnormalities are common and associated with increased morbidity and mortality(1, 2). Both hyponatraemia and hypernatraemia have been reported to occur more frequently in high ambient temperatures, although the underlying mechanisms are not well understood. Global temperatures are rising secondary to climate change, which may impact the incidence of dysnatraemia worldwide.
Aim: To identify, collate and critically appraise studies analyzing the relationship between climate measures (outdoor temperature, humidity) and serum sodium levels.
Methods: Systematic review, reported in accordance with PRISMA guidelines. MEDLINE and EMBASE were searched with relevant key terms (“hyponatr(a)emia”, “hypernatr(a)emia”, “water-electrolyte imbalance”, “dehydration”, “water intoxication”, “electrolyte abnormality” and “climate”, “temperature”, “humidity”, “seasons”, “heatwave”). Studies assessing the effect on serum sodium measurement of raised temperature or humidity versus a comparator were included.
Results: 1354 potentially relevant studies were identified, with 34 meeting the inclusion criteria. Included studies originated from 23 countries spanning all inhabited continents. The majority (30 of 34, 88%) reported a significant association between outdoor temperature and dysnatraemia, predominantly a reduction in serum sodium levels during periods of increased temperature. Humidity did not have a substantial effect on serum sodium level. The eleven largest population-based studies are characterised in Table 1. Specific populations with increased vulnerability to dysnatraemia were identified: the elderly, as well as children, individuals taking medications such as diuretics and antidepressants, with chronic renal impairment or undertaking physical exertion.
Conclusion: An increased incidence of dysnatraemia, particularly hyponatraemia, in association with higher ambient temperature is consistently reported. It can be inferred that hyponatraemia presentations are likely to rise with increasing global temperatures and frequency of extreme heat events secondary to climate change. Evidence-based public health messages, clinician education and reduction in fossil fuel consumption are necessary to reduce the expected burden on healthcare services worldwide(3).