Seasonal plasma electrolyte fluctuations in childhood diarrhoea

Dysnatremia in a changing climate: A global systematic review of the association between serum sodium and ambient temperature

OBJECTIVE

Both hyponatremia and hypernatremia have been reported to occur more frequently with higher ambient temperatures, although the underlying mechanisms are not well understood. Global temperatures are rising due to climate change, which may impact the incidence of dysnatremia worldwide. We aimed to identify, collate and critically appraise studies analyzing the relationship between climate measures (outdoor temperature, humidity) and serum sodium concentrations.

DESIGN

Systematic review, reported in accordance with PRISMA guidelines.

METHODS

MEDLINE and Embase were searched with relevant key terms. Studies assessing the effect on serum sodium measurement of elevated temperature or humidity versus a comparator were included.

RESULTS

Of 1466 potentially relevant studies, 34 met inclusion criteria, originating from 23 countries spanning all inhabited continents. The majority (30 of 34, 88%) reported a significant association between outdoor temperature and dysnatremia, predominantly lower serum sodium with increased ambient temperature. Humidity had a less consistent effect. Individuals aged above 65 years, children, those taking diuretics and antidepressants, those with chronic renal impairment or those undertaking physical exertion had increased vulnerability to heat-associated dysnatremia. The risk of bias was assessed to be high in all but four studies.

CONCLUSIONS

Higher ambient temperature is consistently associated with an increased incidence of hyponatremia. We infer that hyponatremia presentations are likely to rise with increasing global temperatures and the 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.

Sequential recruitment of study participants may inflate genetic heritability estimates

After the success of genome-wide association studies to uncover complex trait loci, attempts to explain the remaining genetic heritability (h ²) are mainly focused on unraveling rare variant associations and gene-gene or gene-environment interactions. Little attention is paid to the possibility that h ² estimates are inflated as a consequence of the epidemiological study design. We studied the time series of 54 biochemical traits in 4373 individuals from the Cooperative Health Research In South Tyrol (CHRIS) study, a pedigree-based study enrolling ten participants/day over several years, with close relatives preferentially invited within the same day. We observed distributional changes of measured traits over time. We hypothesized that the combination of such changes with the pedigree structure might generate a shared-environment component with consequent h ² inflation. We performed variance components (VC) h ² estimation for all traits after accounting for the enrollment period in a linear mixed model (two-stage approach). Accounting for the enrollment period caused a median h ² reduction of 4%. For 9 traits, the reduction was of >20%. Results were confirmed by a Bayesian Markov chain Monte Carlo analysis with all VCs included at the same time (one-stage approach). The electrolytes were the traits most affected by the enrollment period. The h ² inflation was independent of the h ² magnitude, laboratory protocol changes, and length of the enrollment period. The enrollment process may induce shared-environment effects even under very stringent and standardized operating procedures, causing h ² inflation. Including the day of participation as a random effect is a sensitive way to avoid overestimation.