Heat waves and the brain: 9.7% rise in admissions, 2.97% suicides

A dangerous heat wave has hit Western Europe: the UK recorded its highest ever June temperature at 36.1 °C, which felt like about 39 °C. Researchers are now tracing concrete harms to minds and brains, from short-term lapses in attention to measurable rises in hospital admissions and suicide rates.

What do studies show?

In published analyses, heat waves correlate with increased mental-health harms: a 2023 review led by Emma Lawrance found a 9.7% increase in hospital admissions for people with mental-health conditions during heat waves, and Joshua Wortzel and colleagues found a 2.97% rise in suicide rate among US residents aged 15 to 24 for every 1 °C increase in average monthly temperature. Other findings include firefighters becoming harder to focus after 15 minutes of intense heat, with their skills returning after roughly 20 minutes of cooling, and people with schizophrenia being three times more likely to die during Canada’s 2021 record heat wave.

Those results come from a mix of retrospective population studies and targeted field work. The firefighters study gives a short-term, experimental glimpse: 15 minutes of intense heat impaired attention, and a 20-minute cool-down restored performance. The population-level figures show larger-scale impacts: Lawrance’s review aggregates evidence to quantify a near-10% rise in admissions during heat waves, while Wortzel’s Heat-Mind Lab quantified a specific per-degree suicide signal concentrated in young people, a change described as more than double the increase seen in people over age 24.

How might heat harm the brain?

Laboratory and imaging studies suggest several biological pathways: animal experiments show levels of neurotransmitters such as serotonin increase when rats and mice face high temperatures, heat may alter how brain networks communicate, and it can affect how oxygen reaches brain cells; early-life exposure also links to altered brain structure later. Research cited in the coverage reports altered white matter in children who were exposed to extreme heat or cold as babies by the time they were nine to 12 years old.

Those biological signals sit alongside social and behavioral changes induced by heat: people may avoid outdoor activity, get poorer sleep, or reduce social contact, all of which affect mental health. The combination of physiological disruption and degraded sleep or exercise could compound risks, especially for people living with existing mental-health conditions.

Why it matters

People with mental-health conditions are especially vulnerable, Lawrance notes, and the population impacts are not trivial: a 9.7% increase in admissions during heat waves stresses health systems already coping with other climate-linked burdens. The sharp per-degree youth suicide signal identified by Wortzel points to a cohort effect; young people may be disproportionately affected by rising monthly averages. Short-term impairments documented in firefighters show how heat can transiently degrade attention and control, with potential safety and economic consequences for outdoor and emergency workers.

Heat exposure in early life may carry long-term developmental effects. Children born in 2020 are predicted to experience around seven times the number of heat waves their grandparents did, a projection cited by Lawrance that increases the stakes for adaptation and research on developmental impacts.

What to watch

Researchers and public-health agencies should track hospital admissions and suicide rates around future heat waves and try to run prospective cognitive testing during high-heat alerts; Catherine Thompson notes the logistical challenge, saying, "My guess [is] that no one’s done it because it’s just so difficult to do." Policymakers should also monitor whether heat-response measures reduce the 9.7% admissions spike and whether targeted protections reach people with severe mental illness and young people.