Global warming is likely to increase the number of people requiring hospitalisation due to critically low sodium levels in the blood – a condition known as hyponatraemia.
A new study from Karolinska Institutet in Sweden projects that a temperature rise of 2°C would increase the burden on hospitals from this condition by almost 14%.
“Our study is the first to provide precise estimates of how temperature influences the risk of hyponatraemia – findings that could be used to inform healthcare planning for adapting to climate change,” says study first author and the institute’s Department of Clinical Science and Education adjunct senior lecturer Buster Mannheimer.
Climate change is expected to trigger a rise in average global temperatures in the coming decades, resulting in a myriad of heat-related consequences for human health.
One of those is hyponatraemia, which can occur from a variety of diseases such as heart, renal and liver failure, as well as from excessive sweating or fluid intake that dilutes the sodium concentration in the blood.
Our bodies need sodium to maintain normal blood pressure, support the function of nerves and muscles, and regulate the fluid balance in and around our cells.
If blood sodium levels drop, it can lead to nausea, dizziness, muscle cramps, seizures, and even a coma.
It is well known that hyponatraemia cases increase during the summer months in temperate countries.
Still, data on temperature thresholds above which risks amplify have been lacking, complicating clinical planning and predictions of health burden in future climate scenarios.
In the current study, the researchers linked data on Sweden’s entire adult population to information on 24-hour mean temperatures over a nine-year period.
In that time, more than 11,000 were hospitalised with a principal diagnosis of hyponatraemia, most of whom were women with a median age of 76.
Average daily temperatures ranged from -10°C to 26°C.
The researchers found an almost tenfold increased risk for hospitalisation due to hyponatraemia on the hottest days, compared with the coolest periods.
Women and the elderly carried the greatest risk, with individuals 80 years or older 15 times more likely to be hospitalised for hyponatraemia during heat waves.
The incidence of this condition was largely stable from -10°C to 10°C, but increased rapidly at temperatures above 15°C.
When the researchers applied the data to a prognostic model forecasting global warming of 1°C and 2°C – in line with United Nations Intergovernmental Panel on Climate Change (UN IPCC) climate projections for 2050 – they found that hospital admissions due to hyponatraemia could be expected to increase by 6.3% and 13.9% percent respectively.
“We believe these estimates are quite conservative, seeing as we didn’t account for secondary diagnoses of hyponatraemia, extreme weather events or an ageing population,” says study co-last author and the institute’s Department of Laboratory Medicine associate professor Jonatan Lindh.
“Without adaptive measures, this suggests that over the next few decades, rising global temperatures alone will increase the burden of hyponatraemia on healthcare systems.”
It should be noted that Sweden is in the continental climate zone, with buildings adapted mostly for cold temperatures.
Therefore, the thresholds observed in this study may be representative for cool temperate regions only.
The findings are published in the Journal of Clinical Endocrinology and Metabolism.