Global warming intensifies stroke risk: Study links temperature swings to rising stroke burden worldwide

By Tarun Sai LomteApr 24 2024Reviewed by Susha Cheriyedath, M.Sc.

In a recent study published in the journal Neurology, researchers assessed the global burden of stroke attributable to non-optimal temperatures due to climate change.

Stroke is prevalent in older people and may be accompanied by severe sequelae and complications. In 2019, there were 12.2 million cases of incident stroke and 6.55 million related deaths, and it ranked third among the causes of disability-adjusted life years (DALYs). Studies have highlighted increased stroke burden with extreme temperatures. While the relationship between stroke and non-optimal temperatures has been explored, there is limited information about stroke burden and distribution across countries/territories.

Study: Burden of Stroke Attributable to Nonoptimal Temperature in 204 Countries and Territories. Image Credit: Black Salmon / Shutterstock

About the study

In the present study, researchers investigated the global burden of stroke due to non-optimal temperatures. They extracted data on stroke deaths and DALYs from the Global Burden of Diseases (GBD) study by region, country, territory, sex, age, and sociodemographic index (SDI) quintile between 1990 and 2019.

Next, the team computed the monthly average daily mean, minimum, and maximum temperatures. The World Bank databases were used for data on national indicators. The theoretical minimum risk exposure levels (TMRELs) were calculated as the temperatures with the least mortality risk for each year and location.

Cause-specific mortality was estimated. Joinpoint regression models defined the temporal trends of the disease burden; subsequently, the annual percent change of identified trends was calculated. A Bayesian age-period-cohort model was used to predict future trends; it estimated the average annual percent change in age-specific rates, period/cohort effects, and age effects.

A decomposition analysis was undertaken to examine the factors driving changes in stroke burden over time. A fixed-effect panel data analysis was performed to analyze whether national-level indicators were associated with stroke burden attributable to non-optimal temperatures. Besides, SDI-related health inequalities in disease burden were explored.

Findings

In 2019, over half a million stroke deaths and 9.42 million DALYs attributable to non-optimal temperatures were recorded worldwide. The age-standardized rates of stroke mortality (ASMR) and DALY (ASDR) attributable to non-optimal temperatures showed a continuous decline globally. The annualized rates of change in ASMR and ASDR were -0.43% and -0.45% per year, respectively.

Males had a higher burden of stroke than females. Countries with high-middle SDI consistently showed the highest burden, while those with high SDI had the least. The stroke burden declined in most regions between 1990 and 2019. The decomposition analysis revealed that population growth and aging increased the stroke burden while epidemiological changes reduced it.

Across SDI quintiles, stroke deaths, and DALYs showed a sharp increase since 1990, except in high-middle and high-SDI countries. Stroke mortality and DALY rates declined in all age groups, with the most significant reduction in the 0–4 age group. Every one-unit increment in PM_2.5 and carbon dioxide emission increased ASMR by 0.16 and 0.15, respectively.

ASMR was low in countries with lower population density, gross domestic product (GDP), forest area, per capita health expenditure, and physicians per 1,000 individuals. A similar relationship was observed with ASDR. Furthermore, low temperatures contributed more to stroke deaths and DALYs than high temperatures worldwide in 2019.

Since 1990, ASMR and ASDR attributable to high temperatures continuously increased worldwide, whereas those attributable to low temperatures have declined. However, stroke burden due to high temperatures may increase in the future, whereas that attributable to low temperatures may decrease. There was no correlation between SDI and stroke burden attributable to low or non-optimal temperatures.

However, a significant correlation between SDI and stroke burden was observed, attributable to high temperatures. SDI-related health inequalities of high temperature-attributable stroke burden were substantial, and countries with higher SDIs showed a higher burden than lower-SDI countries. Among stroke subtypes, ischemic stroke and intracerebral hemorrhage attributable to non-optimal temperatures were the major contributors to stroke deaths and DALYs.

Conclusions

In sum, the researchers investigated the global, regional, and national burden and distribution of stroke attributable to non-optimal temperatures. While stroke ASMR and ASDR have declined since 1990, the number of deaths and DALYs increased, particularly in low-SDI countries. Older people and males had a greater burden. While low temperatures have been the main contributors to stroke burden, high temperatures have been increasingly contributing to the burden, a trend likely to prevail in the future.