Cognition. A variety of studies support the conclusion that heat impairs cognitive functions:
1) Harvard researchers followed 44 healthy students comparing cognition, focus, processing, reaction times, and memory during a 12-day heat wave. Results showed students who lived in air conditioned dormitories had significantly better function than an equally matched group of students who lived in non–air-conditioned dorms.9
2) Complex cognitive tasks such as working memory (spatial span test, pattern recognition) have been observed to be significantly impaired because of heat stress.10
Insomnia. Sleep is an essential function for overall well-being and health with adverse impacts of sleep deprivation on mood, depression, and cognition. Normal sleep onset and maintenance is triggered by a drop in core body temperature. Increased heat contributes to insomnia and worsens in combination with increased humidity, with the potential to aggravate all psychiatric difficulties and coping abilities.11 This has implications for urban residents who live in areas where heat is trapped and for people who do not have access to air-conditioning or cool respite places.
Especially vulnerable psychiatric patients
Patients with severe psychotic or mood disorders, substance abuse disorders, or cognitive impairments, who are able to compensate with marginal executive functioning during periods of normal weather, are challenged during intense heat and can lose their fragile ability to make plans, have good judgment, and effectively care for themselves. These patients are more likely to experience heat stroke and other heat-related morbidity. Evidence supports these impacts on psychiatric patients:
• Emergency department utilization and hospitalization increase for patients with preexisting psychiatric illness during heat waves12,13
• Preexisting mental illness alone raises the risk of mortality during extreme heat events 2- to 3-fold14,15
• Patients with schizophrenia may have underlying impairments in thermo-regulation (intrinsic to the disease), which might explain the perplexing sight of psychotic patients bundled up in layers on hot days16
• Psychiatric medications (eg, antipsychotics, anticholinergic antidepressants) have the potential to impair the body’s heat regulatory functioning; sweating and dehydration can increase lithium levels, putting patients at greater risk for dangerous toxicity during heat waves17
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18. Centers for Disease Control and Prevention. Climate Change and Extreme Heat Events. https://www.cdc.gov/climateandhealth/pubs/ClimateChangeandExtremeHeatEvents.pdf. Accessed May 8, 2019.