Eating a banana or two a day could make you sleep much better in the hot weather by helping your heart to function normally and reducing the risk of night cramps, according to a leading sleep expert.

Avoiding heavy meals and strenuous exercise close to bedtime can also make for a hot night’s sleep and should be avoided, according to Professor Russell Foster, a body clock specialist at Oxford University who has shared his top tips on surviving the heatwave with i.

When we sweat, we lose potassium – a type of mineral known as an electrolyte – which is involved in muscle contractions, heart function, and regulating water use in our systems.

It also helps maintain normal blood pressure by limiting the effect of sodium, or salt and with kidney function.

So it’s important to eat foods rich in potassium, with bananas being a particularly good bet, he said.

“When we sweat we lose potassium, which is really important for the functioning of the nervous system. You can start to feel pretty ropey if you sweat a lot and you can get muscle cramps at night – so keeping potassium up is important,” Professor Foster said.

“One or two bananas a day would be recommended because they’re a good preventative measure – and lots of fresh vegetables,” he added.

Green vegetables are a good source of potassium, along with fruits such as avocados, tomatoes and oranges – while a general vitamin and mineral supplement will also help, Professor Foster said.

Although specific potassium supplements do exist, they can only be accessed with help from your GP. They are prescribed to counteract side-effects of various drugs, so they are not available to the general public for more general reasons, such as to combat heat, says Professor Foster, who has just written a book about how to improve health through better sleep.

He is already an advocate of a light, early dinner, arguing that a heavy meal close to bedtime increases the risk of turning those calories into fat rather than burning them up with daytime activities.

But the argument for a lighter, early evening meal becomes even stronger in the very hot weather, he says.

“It’s a good idea not to eat heavy meals before bed because you’re shunting blood to the stomach and the digestive system – but when you’re hot you need to shunt blood to the hands, feet and skin to cool down.”

Professor Foster has shared several other recommendations for how to keep cool at bedtime, starting with the preparations for sleep.

• Have a cool or lukewarm shower or bath just before going to bed. This cools the body directly and can help reduce the temperature of your skin. But don’t overuse soaps as this can encourage yeast or fungal growth – causing itching. • Wet your face and arms with a wet towel, or use a water-filled spray bottle, then stand in front of a fan. • Soak your feet in cold water or a cold water bottle for 10 minutes before going to bed, as heat is lost more quickly through your extremities (feet and head) or put your socks in the fridge. Wetting your hair is another alternative. • Apply ice packs to the skin. This will help cool you down.

Extreme heat can affect your ability to fall asleep, stay asleep and feel refreshed from sleep. • Chose the coolest part of the house to sleep in, if not your bedroom. A quiet, dark and cool area will improve your sleeping pattern – e.g. cellar. Sleep downstairs if you can, as heat rises. • If you sleep with your pet – It is time to find them a different place to sleep! • Maybe sleep alone. • Use fans in an adequately ventilated area. Make sure the room you are in has an open door or window so fresh air can flow through the room.

• Drink plenty of water during the day to keep your body hydrated and cool while you sleep. Dehydration is a common cause of not being able to get to sleep (insomnia). Keep a glass/insulated container of cold water by your bed in case you wake up hot and uncomfortable. • Lots of sweating can cause muscle cramps – related to low potassium – so, eat fruits such as bananas with a high potassium content. • When using a fan, have the bedroom door open to allow for airflow. • Place a tray of ice cubes in front of the fan will cool the air blown around the room • Wear no clothing or lightweight, loose-fitting clothing, preferably made from natural fibres such as cotton or linen that allows air to circulate around the skin. Avoid synthetic fabrics. • If you need to have a sheet over you, try leaving your feet out of the sheet, as body heat will escape via your feet. • Can place bedding in the deep freeze and remove prior to sleep. • Using a water spray mister on your face and body to create a fine mist can be cooling. If you wake up during the night, repeating this will also help. • Freeze a gel-filled eye mask and put it on at bedtime. • Moisturise dry skin before bed with an aloe vera-based after-sun cream, ideally kept in the fridge.

• Keep your home as cool as possible by drawing the curtains and blinds during the hottest part of the day. Keep the windows closed. • At night – open-up the house to allow cool breezes to circulate. • If you use fans, ensure room is well dusted and cleaned to avoid allergens – and triggering asthma or sneezing.

• Avoid exercising close to bed time, as it will increase your internal temperature. If you choose to exercise, exercise several hours before bed time to allow your body the opportunity to cool down. • Overall reduce your activities. • Avoid hot, heavy or spicy food/meals near bedtime. • Avoid caffeinated drinks (tea, coffee, and energy drinks) in the late afternoon or evening, as these can keep you awake.

• Ancient Egypt – ancient Egyptians used to rest their heads on pillows made of stone – designed to keep the head elevated while sleeping and allow air currents to flow under the head and cool the sleeper. These headrests were made of marble, ivory, ceramics, stone, wood, and even glass were found in Egyptian tombs from 3000 BC until 30 BC. Today Egyptians dampen a sheet or towel in cool water and using it as a blanket. • How India copes with heatwaves – recommendations are straightforward – people should drink lots of water – and adopt the tips discussed. In rural parts of India people cut an onion in half and rub it on their body. Houses were traditionally designed with thick, insulating walls of both mud and mortar, high indoor ceilings and thatch roofs – all factors that helped keep the home cool in summer. Whitewashing the roof of a house brings down the indoor temperature by 5-10 degrees – making it cooler at night. The rich 2 per cent of the population use air conditioners.

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