Why does hot weather make you feel tired?

By Camilla Foster

As temperatures rise significantly across the UK, you might find yourself yawning more often at your desk and finding it harder to stay focused.

This sense of tiredness and sluggishness isn’t just the result of a poor night’s sleep – it could actually be your body working harder to cope with the shift in temperature.

We spoke with experts to uncover how hot weather impacts our bodies and why it often leaves us feeling drained and tired.

What physiological changes happen in the body when it’s hot that contribute to feelings of fatigue?

“When it’s hot, the body must work harder to maintain homeostasis, which is defined as the process by which the body maintains a stable internal environment,” explains Kieran Turner, health and wellbeing physiologist at Nuffield Health. “In order to do this, the heart has to exert more effort to circulate blood flow towards the skin so that heat can radiate away, contributing to an increased workload and therefore feelings of fatigue.”

Dr Lalitaa Suglani, psychologist and author of High-Functioning Anxiety, agrees and adds: “Psychologically, your body being under heat stress can cause a low-level survival response.

“The brain perceives the heat as a physiological stressor, leading to a dip in energy, motivation, and mental stamina – so your body is working harder. This can then impact on concentration and staying focused.”

What role does dehydration play in heat-related tiredness?

“Dehydration plays a significant role in heat-related fatigue by disrupting multiple physiological systems,” says Turner. “It impairs the body’s ability to thermoregulate through efficient sweating, compromises nutrient transport, and hinders ATP production, all of which reduce physical energy.”How does high temperatures impact brain function?

“High temperatures negatively impact brain function and alertness by causing thermal stress that disrupts neurological functions,” says Turner. “This effect is intensified by dehydration, which reduces blood flow and oxygen delivery to the brain, impairing attention, memory and mental clarity.

“Additionally, heat often interferes with sleep quality, leading to increased daytime fatigue and decreased executive function.”

Emotional fatigue can also set in during heatwaves, adds Suglani.

“We become more irritable, less patient, and more mentally taxed simply because our body is trying to stay cool,” says Suglani. “Emotional regulation takes more effort when the body is overheated, as this is not the body’s priority.”

Are some people more vulnerable to heat fatigue than others?

“The elderly have a less efficient thermoregulatory response which is amplified by their tendency to have lower levels of thirst, which can contribute to heightened dehydration and therefore fatigue,” explains Turner. “Similarly, children have a less efficient thermoregulatory response, and because they have a greater surface area to body mass ratio, they may gain heat faster.”

People with certain health conditions are also more vulnerable to heat fatigue.

“Those with cardiovascular diseases will have impaired blood flow, thus reducing their capability to thermoregulate through heat radiating away from their blood near the surface of their skin,” says Turner. “Whilst those with diabetes may have damaged blood vessels and nerves, potentially inhibiting the person’s sweat response if the nerves that control their sweat glands are damaged.”

Can hot weather disrupt your sleep patterns, and if so, how does that affect fatigue during the day?

“When it’s too warm, people often experience restless sleep, frequent awakenings, or difficulty falling asleep at all or do not enter into the deeper sleep where we process,” says Suglani. “This leads to cumulative sleep debt, which has a direct impact on mood, attention, and daytime energy levels.

“Many people report feeling sluggish, unmotivated, or even more anxious during heatwaves due to this disrupted sleep.”

Are there times of day when heat fatigue is more pronounced?“The body’s natural temperature typically peaks in the late afternoon, which often coincides with the hottest part of the day, making heat fatigue more pronounced when these two factors combine,” says Turner.

Here are some ways to stay energised during a heatwave…

Stay hydrated

“Hydrate often, even mild dehydration impacts mental clarity and mood,” says Suglani. “Keep on top of water, have it next to you and keep sipping.”

Take breaks

“Take micro-rests throughout the day, not just physically but mentally too,” advises Suglani. “Step away from screens, overstimulation, demanding tasks and your phone.”

Try some cooling techniques

“A cold compress on the wrists or neck can reduce body temperature and ease overstimulation,” says Suglani.

Modify expectations

“Understand that your energy will naturally dip, and give yourself permission to slow down and not put these high expectations on doing all your things, as most likely you won’t be able to,” suggests Suglani. “Offer compassion to yourself.”

Avoid overstimulation

“Loud noise, bright lights, and high demands drain more energy when you’re already heat-fatigued,” says Suglani.

Practise breath work

“Short, slow breathing helps reset the nervous system and regulate fatigue, especially as our breathing can be impacted too by the heat,” says Suglani.

Eat lighter meals

“Lighter meals help prevent additional internal heat production,” notes Turner.

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