Is the Heat Affecting your Sleep? Strategies for Better Rest

Rising temperatures due to climate change are affecting our sleep, which in turn is affecting our health, performance and well-being. How can we adapt to the heat?

Have you ever thought that climate change could affect your sleep? As temperatures rise, heat can increasingly disrupt our sleep, especially during the summer months.

Most of us have experienced the benefits of a good night's sleep: improved cognitive performance, greater productivity and better mood the next day. And that's because sleep is an important health outcome. The quantity and quality of our sleep determines our risk of developing mental, cardiovascular and metabolic diseases, cancer and accidents.

Sleeping in the heat: the body on alert

Heat (and cold) challenge our bodies to maintain a core temperature within the normal range required to support physiological function and sound sleep: this process is called thermoregulation. In a hot sleeping environment, thermoregulation is challenged and heat production can exceed heat loss beyond tolerable levels, raising core body temperature and disrupting our natural sleep-wake cycle with increased wakefulness.

Here we summarise the findings of our recently published systematic review that examined the role of heat on sleep. We also discuss climate adaptation strategies and provide potentially useful tips to help you protect your sleep as the thermometer rises.

Science says: heat is associated with worse sleep

In the current review, we focused on the role of heat on sleep as measured in real-life settings, for example using subjective sleep questionnaires and activity monitors.

Most of the articles reviewed (29/36, 80%) explicitly concluded that higher temperatures were associated with poorer sleep

After a thorough review of the literature, 36 articles were included, covering countries from all continents and samples of different ages, from adolescents to older adults. In terms of results, most of the articles reviewed (29/36, 80%) explicitly concluded that higher temperatures were associated with poorer sleep. This negative effect of higher ambient temperature on sleep was stronger in the warmest months of the year, in vulnerable populations, especially the elderly, and in the warmest regions of the world. This finding was consistent across different sleep indicators, including sleep quantity, quality and timing, and whether temperatures were measured indoors or outdoors, during the day or at night.

We now need to test what works effectively

Beyond observational studies, we identified an urgent need for interventions to promote heat adaptation at different levels, from individual interventions to structural changes.

Individual level interventions. At an individual level, many factors are known to affect our sleep and could be relevant in the context of heat.

• These include avoiding caffeine, nicotine and alcohol.
• Sleep schedule regularity, i.e. getting in and out of bed at relatively fixed times, is also known to be a key factor in good sleep hygiene.
• Managing other environmental disturbances, such as noise and artificial light, is also important.
• Although there is no scientific evidence to support heat-specific behavioural adaptations, such as taking a cold or lukewarm shower before going to bed and using fans and water sprays, these strategies are worth trying and may help to maintain restorative sleep in hot environments.
• Finally, encouraging regular physical activity is also crucial, given the role of physical fitness in heat adaptation.
• Mental health is also closely linked to sleep, so interventions such as stress management and cognitive behavioural therapy may help some of us to maintain restorative sleep.

Although air conditioning may be a good short-term solution in some specific situations, our work does not strongly support its use to maintain good sleep in most environments

Air conditioning. Specifically for air conditioning, some of the studies included in our review indicated a lack of thermoprotective effect on sleep. Air conditioning also required increased energy consumption, which is incompatible with climate change policies. Therefore, although air conditioning may be a good short-term solution in some specific situations, our work does not strongly support its use to maintain good sleep in most environments.

Structural interventions. At the structural level, environmental interventions such as urban greening, urban water features, passive cooling and improved building insulation and ventilation systems should also be rigorously assessed for their ability to promote and protect sleep during hot periods. For example, although building (re)insulation is often presented as a solution to save energy for heating in winter, it may also have significant health co-benefits, particularly in relation to summer heat. Further studies are needed to test the conditions under which these strategies can improve sleep in hot conditions.

Environmental interventions such as urban greening, urban water features, passive cooling and improved building insulation and ventilation systems should also be rigorously assessed for their ability to promote and protect sleep during hot periods

In a hotter world…

Our review shows that:

• Higher temperatures are generally associated with poorer sleep outcomes worldwide.
• In the absence of robust evidence for rapid sleep adaptation to heat, rising ambient temperatures induced by climate change pose a serious threat to human sleep and, in turn, to human health, performance and well-being.

We argue that field experiments are now urgently needed to promote adaptation and safeguard the essential restorative role of sleep in a hotter world. These interventions should test both individual and structural strategies, alone or in interaction.