How to get a good night’s sleep when it’s hot and light outside

How to keep cool at night during hot weather and heatwaves
Sleeping in hot weather is no picnic, so here’s how to keep cool

There are plenty of reasons to celebrate summer, now that it’s finally here, but a good night’s sleep is probably not one of them.

You toss and turn, flipping the pillow over and over to try to find the cool side, coated in a sticky sheen of sweat. And the extra daylight is a mixed blessing, making it harder to drop off  and trickier to stay asleep once we do.

Light evenings tend to reset our body clock that’s located in our brain. Research shows that light later in the day makes it more likely we’ll wake up in the night and we’ll get less restorative slow wave alpha sleep too. Unfortunately, this is exactly the type we need to feel rested in the morning.

“Our sleep cycle is governed by our sense of light and dark, or circadian rhythm,” explains Dr Guy Meadows,  the co-founder and clinical director of the Sleep School app.

The longer we see light, the longer our in internal clock tells our body it is daytime and needs to stay alert.

When it gets dark the body clock signals that it’s time to sleep by releasing melatonin. In summer months we secrete less melatonin, which one reason we wake up earlier and find it harder to drop off.

How to sleep better in the light and heat

Reducing light use before you head to bed is important, Meadows says. So resist the urge to bask in  the evening light.

The same rules apply, as in winter. Draw your blinds to dim the light a good couple of hours before you’re ready to turn in, so that your body begins to step up melatonin production. And don’t forget to switch off electronic devices.

You might also want to invest in blackout blinds - John Lewis do a good range - or at least a sleep mask.

Look for masks with adjustable straps that will stay in place and deliver a comfortable, full-blackout.

Temperature is another incredibly important facet of falling asleep, explains Dr Meadows.

He says: “Our core body temperature plays an important role in the regulation of sleep. At the start of the night, a 1C drop in temperature is needed to help you fall asleep.

“It’s this decrease, coupled with the arrival of darkness, that informs the internal body clock that the night has begun. This triggers the release of the sleeping hormone melatonin, helping you fall asleep.

“We sleep better in a cool room, compared to a warm room, with the ideal temperature reported to be 16C-17C,” says Dr Meadows, although that does take into consideration that most of us wear something to bed and use various amounts of bedding.

What temperature is too hot to sleep in?

It goes without saying that different people will have different tolerances for the temperatures they can sleep in. Someone who lives in Arizona will be more used to the heat than another person from Siberia. Similarly, young children and older people tend to require a slightly warmer sleeping environment.

However, the mercury needn’t be soaring for it to prove difficult to sleep. A 2020 study from Waseda University in Japan found that it becomes more difficult to sleep when the temperature climbs over 24C.

What are the effects of sleeping in a hot room?

Ultimately, trying to rest in a hot room will make it harder to fall asleep and you’ll sleep less efficiently once you do.

Another study, published in 2012 by scientists at Tohoku Fukushi University, also in Japan, found that increasing the temperature in a bedroom by 6C meant sleepers spent 6.8 per cent more time awake and reduced their sleep efficiency by seven per cent.

One 2015 study, again from Japan, found that the slow-wave (deep) sleep that our body uses to heal and restore itself is reduced when sleeping in the heat. This means that the following day, fatigue is far more likely.

How to sleep better in the heat

“Sleeping well in the heat involves mastering the art of controlling that which you can change, and accepting that which you can’t,” advises Dr Meadows.

“There are many practical actions that you can take to keep cool during a heatwave that will promote better sleep. However, sometimes adopting an accepting attitude can be the best approach.”

Keep your head cool by keeping a cool head

Dr Meadows adds: “Getting frustrated and restless because you’re too warm only makes your body generate more heat, keeping you awake for longer. Keep cool by lying still and accepting the heat.

“Try focusing your attention on the discomfort and describe what you feel objectively and without judgment, such as ‘I feel heat and sweat on my face, neck and back’. Learning to change your relationship with the heat helps defuse its power and lead to better sleep.”

Prepare for cooler sleeping during the daytime

It might sound counterintuitive, but keeping your curtains closed can stop your bedroom getting warm in the first place, making it easier to fall asleep at night. Another thing to do is to avoid a late dinner.

“Eating food close to bedtime elevates your body temperature, making it harder to sleep,” says Dr Meadows. “For the best night’s sleep, leave at least two hours between eating and sleeping – and limit alcohol consumption.”

Wear cotton pyjamas or sleep naked

“If you’re wearing natural fibres like cotton, then you’ll feel cooler in the night than if you were naked, because the cotton will wick away sweat from your skin,” says Dr Alanna Hare, an NHS and private sleep consultant at the Royal Brompton Hospital.

“However, anything man-made or synthetic will keep heat next to your skin. And the same goes for bedding. So if I had the choice between cotton and nakedness, I’d choose cotton. But if you’re choosing between man-made fibres and nakedness, go naked.”

Create a breeze

“Sleep with the window open or keep a fan on during the night to add an extra breeze in your bedroom,” Dr Meadows advises.

If you want to keep things extra cool, place a frozen bottle of water between yourself and the fan to cool the air as it comes towards you. (Modern air coolers can chill the room by a few degrees using this principle.)

Make a ‘cold water bottle’

“Simply fill a hot water bottle with cold water and keep it in the fridge or freezer for a few hours before bed – if you’re an extra hot sleeper, you can leave it in a little longer,” suggests Chris Tattersall, a sleep expert at bedding manufacturer Woolroom.

“Then snuggle up with your ice pack under the covers or leave it to cool down the bed before jumping in – it’s one of the best ways to keep cool at night.”

Ditch the memory foam

“The synthetic materials used in a memory foam mattress mean that it’s not breathable and doesn’t absorb moisture, leaving your body to overheat and sweat while in bed,” says Tattersall.

“You know that sinking feeling you get when you sleep on a memory foam mattress? For that to happen, it needs body heat to warm it up, which is then reflected back onto you as you sleep.

“Overlaying your memory foam mattress with a wool mattress protector will help regulate around 75 per cent of that heat, helping you stay cooler on those hot summer evenings.”