Persistent heatwaves are significantly impacting sleep quality, leading to widespread fatigue, lethargy, and irritability, according to sleep experts. The disruption affects cognitive function, emotional regulation, and even immune response, with women potentially experiencing more severe effects due to hormonal fluctuations.
Research indicates that a substantial portion of adults lose sleep due to high night-time temperatures. A UK study found that 48% of adults regularly lose sleep because they are too hot, and a YouGov poll revealed that two in three people struggled to sleep during a recent heatwave, with nearly half losing at least three hours of sleep per night. This prolonged lack of restorative sleep can impair the ability to think clearly and control emotions.
Physiological Impacts of Heat on Sleep
Experts explain that the body's core temperature must lower to initiate and maintain sleep. In warm conditions, the body struggles to achieve this necessary temperature drop. Maja Schaedel, a clinical psychologist and director of the Good Sleep Clinic, states that the ideal bedroom temperature is between 16C and 18C (61F and 64F), making warm summer nights a significant obstacle to restorative sleep. Professor Russell Foster, a professor of circadian neuroscience at the University of Oxford, notes that elevated core temperatures in hot weather can prevent the deep wave sleep essential for recovery.
When the body is too warm, it works harder to cool itself. This increased effort involves a faster heart rate and quicker breathing, physiological responses that mimic alertness and make it difficult for the brain to recognize that it is safe to sleep. This heightened activity can also lead to exhaustion, as the body expends energy to cool down, generating additional heat in the process.
Some research suggests that the fatigue experienced during heatwaves may be linked to similar neural pathways activated when the body is ill, with specific neurons inducing feelings of tiredness. Sleep fragmentation, characterized by frequent waking, is also common during heatwaves, leading to earlier than usual awakenings.
Vulnerability and Health Consequences
Women can be particularly susceptible to heat-induced sleep disturbances. Professor Foster explains that hormonal shifts, such as the rise in body temperature before ovulation or hot flushes experienced by menopausal women, can exacerbate the effects of high ambient temperatures on core body regulation. These hormonal fluctuations can cause sufferers to feel even warmer.
In the short term, insufficient sleep can impair emotional and cognitive responses, making it inadvisable to make significant decisions. Furthermore, sleep deprivation can weaken the immune system by increasing the body's stress response and elevating cortisol levels, a stress hormone that suppresses immunity.
Many homes are ill-equipped to handle extreme heat, with a previous study indicating that one in five homes lack adequate shading or ventilation. This inadequacy contributes to the difficulty in maintaining a cool sleeping environment.
Strategies for Improving Sleep in the Heat
To minimize the impact of heat on sleep, experts recommend several strategies. Keeping windows shut and curtains or blinds closed during the day can help trap cooler air inside. Fans can be used to circulate air, and one suggestion is to place a fan facing an open window to help push warm air out.
Professor Foster advises opening windows in the evening once the temperature drops below 20C (68F), creating airflow by opening windows on opposite sides of the house or doors. Taking a tepid bath or shower before bed can also aid in cooling the body. While a cold shower might seem intuitive, it can cause blood vessels to constrict, potentially reducing heat loss from the skin. A tepid bath, however, dilates blood vessels near the skin's surface, facilitating heat release and helping to lower core temperature.
For bedding, suggestions include placing sheets in the freezer for a short period to make the bed feel cooler, or using a hot water bottle filled with ice and cold water. The Scandinavian sleep method, using separate lightweight sheets or duvets, can also help individuals manage their own temperature.
If awakened by heat during the night, a warm, damp flannel wiped over the skin can help the body cool down through evaporation. Experts also recommend avoiding prolonged periods of tossing and turning in bed. Instead, engaging in a quiet activity like reading in a cooler part of the house before returning to bed when feeling sleepier can be beneficial. Keeping the room dark with an eye mask and avoiding screen time are also advised to prevent stimulating the brain and making it harder to fall back asleep.
Combating Daytime Tiredness
For those experiencing fragmented sleep due to heatwaves, catching up on lost sleep can help alleviate daytime tiredness. While regular sleep schedules are generally encouraged, some flexibility may be necessary during extreme heat. Lying in a bit longer in the morning or on weekends can help compensate for lost sleep, though this should not be a long-term practice as it can disrupt the body clock.
Napping can be a useful tool, but timing is crucial. Naps should ideally be taken during the natural dip in the circadian rhythm, typically in the early afternoon. Short naps of 20 to 30 minutes are recommended to avoid grogginess and further sleep disruption at night.
Addressing 'Fan Cough'
Sleeping with a fan on can lead to 'fan cough,' a condition where blowing air directly onto the face can dry out the mucous membranes of the nose, mouth, and throat. This dryness can lead to irritation and increased mucus production, resulting in a cough. Dust accumulation on fan blades can also contribute to airway irritation and coughing.
To mitigate this, placing a bowl of cool water in front of or beneath a fan can add moisture to the air. Experts also advise against pointing fans directly at the face, suggesting instead to direct the airflow towards the body to facilitate cooling through air movement over the skin.