Climate factors and child health in Sweden: a nationwide whole-population study of 4.6 million school-aged children
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Background
Short-term weather conditions can trigger paediatric hospital admissions, but evidence remains limited on the health relevance of intraday temperature variability, humidity, and precipitation, and generally on which subgroups are most susceptible.
Methods
We conducted a nationwide case time-series study of Swedish children and adolescents aged 6–18 years using linked register data. Associations between daily mean temperature, intraday temperature variability, relative humidity, and precipitation and inpatient hospitalisations were estimated with Poisson regression (individual fixed effects) combined with distributed lag non-linear models over lags 0–21 days. Outcomes included all-cause hospitalisation and cause-specific admissions. Effect modification was examined by sex, age group, socioeconomic indicators, region, and calendar periods.
Findings
Among 4,638,247 children and adolescents in the cohort, 1,070,702 (23.1%) experienced at least one inpatient hospitalisation, contributing 1,736,169 hospitalisation events. All-cause hospitalisation increased with higher mean temperature, with risk highest at hot extremes. Intraday temperature variability showed a U-shaped association, with higher rates at both lowest and highest exposure levels. Relative humidity showed no association with hospitalisation risk. Higher precipitation was associated with increased hospitalisation risk, but estimates at high rainfall levels were imprecise. Stratified analyses indicated modest differences by sex and socioeconomic indicators, but clearer heterogeneity by age and region, with the highest risks among younger children and in East Sweden; associations varied across calendar periods and were imprecise for most cause-specific outcomes. Sensitivity analyses mostly showed that the main curve shapes were robust.
Interpretation
Short-term exposure to hot temperatures, both low and high intraday temperature variability, and higher levels of precipitation were associated with an increased risk of all-cause hospitalisation among children in Sweden, with clearer variation by age group and region than by sex or socioeconomic position. These findings support targeting paediatric climate-health preparedness and early-warning systems toward younger children and higher-risk regions such as eastern Sweden and extending such systems beyond mean temperature to include intraday temperature variability, a distinct, currently overlooked driver of risk that heat-focused systems are not designed to capture.
Fundings
This research was funded by Formas, the Swedish Research Council for Sustainable Development (grant no. 2023-01774 and 2022-01845) and the Swedish Research Council (2025-02804 and 2022-06599).
Research in context
Evidence before this study
We identified epidemiological studies examining climatic exposures and hospitalisation among children, published in any language up to June 26, 2026, in MEDLINE, Embase and Web of Science. Search terms combined paediatric populations and hospital admissions with climate exposures and DLNM (e.g., (child OR paediatric*) AND (hospital* OR admission*) AND (temperature OR heat OR cold OR “diurnal temperature range” OR “temperature variability” OR intraday AND humidity OR precipitation OR rainfall) AND (DLNM OR “distributed lag” OR case-time series* OR case-crossover*) (n = 2526). Previous studies have reported associations between ambient temperatures and increased risk of paediatric morbidity, particularly for respiratory and infectious diseases. However, evidence is often limited to smaller exposed groups, single healthcare settings or geographic areas, cause specific outcomes, aggregated data, and incomplete assessment of lagged effects and subgroup vulnerability. Analyses of different climatic exposures, such as temperature, humidity, and precipitation, remain rare.
Added value of this study
Our study used linked whole-population register data from more than 4.6 million school-aged children and adolescents aged 6–18 years in Sweden. This is one of the largest whole-population cohort studies of individual-level climate–health associations in children internationally, and the first such study in the Nordic countries to examine the short-term associations between climatic exposures and hospitalisation risk for children. We found that daily mean temperature and intraday temperature variability were each associated with all-cause hospitalisation, with higher risks at hot temperature extremes and at both low and high levels of within-day temperature variability. Relative humidity showed no association, whereas higher precipitation was associated with increased hospitalisation risk, although estimates became statistically weaker and more imprecise at the highest rainfall levels. The study has several important strengths: it examines different climatic exposures within a single analytical framework; it assesses heterogeneity by age, sex, socioeconomic indicators (parental education and household income), region, calendar period, and parental medical history, showing that risk was highest among younger children and in East Sweden; it evaluates lag-specific and cause-specific associations, showing that heat-related risk was concentrated within the first week of exposure while cause-specific estimates were less precise; and it uses individual-level adjustment for time-invariant characteristics through a within-person case time-series design, controlling for time-invariant individual characteristics and therefore strengthening causal interpretation.
Implications of all the available evidence
The chief implication of this study for public policy is that paediatric hospitalisation risk rises in the days following temperature extremes and periods of high intraday temperature variability, with the largest effects among younger school-age children (6–13 years) and in East Sweden. This supports practical measures such as ensuring reliable access to hydration and shifting the timing of outdoor activity to cooler parts of the day, and, at the healthcare-system level, regionally targeted paediatric surge planning; for example, aligning staffing and emergency capacity with forecasted periods of extreme or highly variable temperature. The chief implication for scientific understanding is that within-day temperature variability represents a distinct dimension of climate-related risk not captured by mean or maximum temperature alone, suggesting heat-health frameworks and early-warning systems built on mean temperature capture only part of the risk. The U-shaped association, with increased risk under both very stable and highly variable conditions, indicates that temperature variability carries information beyond mean thermal load and warrants further investigation. Future research should test whether incorporating variability–metrics improves prediction of paediatric admissions and whether these patterns generalise beyond high-latitude settings.
