Why does heat make me tired - and how can I stay awake? Doctor reveals all

If a stranger walked into my house during a heatwave or hot spell, they might wonder if we’d been burgled. Clothes on the floor, beds unmade, piles of items on the stairs - everything is abandoned when it’s hot. I just can’t find the energy to do anything, apart from moan about being sweaty and tired.

There are many reasons why higher temperatures make us feel tired, from not being able to find the right sleeping position for the heat, to our bodies having to work harder to keep us cooler. Research has actually shown that women feel the effects of heatwaves more than men. GP Dr Amir Khan, woman&home's resident doctor, recently told ITV host Lorraine Kelly that women sweat less than men and our hormones can make us feel hotter.

“Oestrogen and progesterone can affect how your body regulates temperature, and menopause and hot flushes can make things so much worse,” he tells Lorraine. Body size and blood volume can also make it harder to cope with the heat.

"Women also tend to have smaller hearts and narrower blood vessels, so shifting blood around the body to get rid of excess heat may be slightly less efficient than that of a man's,” Dr Khan explains.

Another reason why we might feel extra tired could be our iron levels. Dr Khan explains that “women are much more likely to be low in iron because of periods. And if your iron levels are low, hot weather can leave you feeling absolutely wiped out, dizzy, and exhausted”.

Dr Ian Cole, GP at King Edward VII's Hospital, says while our bodies are designed to protect us from the heat, our energy levels will still be affected. "The middle layer of the skin, or dermis, stores most of the body's water. When we get into higher temperatures, our bodies send fluid from this layer and blood to the skin's surface to cool down," he says. "This depletes your body's water resources and can leave you feeling fatigued."

Dehydration is of course also more of a risk when we’re hot and sweaty. When we get too warm, we can lose precious minerals from our body, such as potassium and sodium, which we need to maintain our electrolyte and glucose stores.

Exercising at the hottest times of day can also leave us dehydrated and tired. Emily Servante, personal trainer at Ultimate Performance, says: "In searing temperatures, you do need to be sensible. Exercising outdoors when it's slightly cooler, preferably early in the morning or later in the evening, is better than crunching out a session in the midday heat."

Tips for staying awake

Stay hydrated

As we’ve said above, sweating more than usual and not replacing lost fluid with plenty of water will make you feel lethargic. "Please stay hydrated and drink plenty of water," Emily stresses. "And water is important, not sugary drinks. If you can, look to drink high-quality products that contain electrolytes, which help to maintain our body's hydration levels."

Also add some hydrating foods to your plate for each meal, such as cucumber, tomatoes, celery, watermelon or lettuce.

Avoid the sun

Staying out of direct sunlight will keep you cool and preserve your energy. This could mean sticking to the shade or staying indoors during the hottest time of the day.

If your home feels hot, make sure to cool it down by closing the curtains and keeping your bedroom cool. Wear a hat and sunglasses to protect your head and keep your body cool.

Eat light meals

"Foods which are easy to digest are best consumed during a heatwave as our body temperature is already elevated," nutritionist Jenna Hope explains.

"Digesting heavy foods can contribute to raising body temperature and make us feel even hotter." Heavy meals also make us feel sleepy and lethargic. Opt for lighter dishes like omelettes, fish, salad, smoothies, yoghurt, and fresh fruit.

Move your body

We don’t have to stop exercising during a heatwave. We just need to adapt how and when we do it. You could go for a cooling 10-minute swim rather than a run around the park. This will still get your endorphins flowing and help you stay awake and energised throughout the day.

Choose an air-conditioned gym or work out at cooler times of the day.

Optimise your sleep

We’re not talking sleep gadgets and gizmos here - it’s much simpler than that. If the heat is draining you and you want to sleep better, there are a few key things you can do.

Firstly, think about your bedtime routine. As tempting as a cold beer or glass of wine might be on a summer evening, alcohol makes our sleep worse - as does caffeine and exercising too late into the evening.

As well as keeping your bedroom cool, wear loose cotton pyjamas and sleep under a cotton sheet. This material is heat-wicking and will keep you cool. You could always even move downstairs if it’s cooler to sleep there, and Dr Cole says: "Fans help with airflow, but don't rely on them to cool down as they don't work over a certain temperature. If it's hot, all they do is move warm air around. That said, placing a bowl of ice cubes in front of a fan can help cool the air down."

While heatwaves are becoming more common in the UK, feeling lethargic and tired in the heat can still be worrying - but there are only a couple of instances where you need to be concerned for your health.

"Heat exhaustion is not usually serious if you can cool down within 30 minutes," explains Lloyds Pharmacy's pharmacist Anshu Kaura. "If it turns into heatstroke, however, it needs to be treated as an emergency."

The difference between heat exhaustion and heat stroke is in the temperature. While exhaustion will leave you with symptoms like tiredness and sweating, heat stroke is when your body tips over 103F (39C). Other symptoms of heat stroke include fever, shortness of breath, confusion, headaches, nausea and fainting.