Southern and eastern Britain has experienced a mini heat-wave. The hot, humid weather across parts of Britain has made for uncomfortable nights. The Met Office says temperatures will now fall slightly but humidity will remain fairly high at 60-80%. Humidity is a big part of the problem, making it hard for sweat to evaporate. For many, getting to sleep will have been sweaty and uncomfortable, closer to the climate people associate with Bangkok than Bangor, either Northern Ireland or Wales.
In places like the US, where powerful air conditioning units are reasonably common in houses in hot and humid areas, it's not so much of a concern. But in places like the UK where it's hot and humid less frequently how should people ensure they get a good night's sleep? There are certain recommendations common in Mediterranean countries. "I make sure all the curtains are closed during the daytime to stop the sun coming in. I have the windows open on the shady side and closed on the sunny side. It means running round the house halfway through the day to close one side and open the other." An hour before going to bed, open all the windows to get a through breeze.
But not everyone has the luxury of being able to throw open windows. It may not be safe. Bungalows, ground floor flats and basements can be vulnerable to burglary. Others may worry about insect bites, particularly with the spread of mosquitos. "The most sensible option is to use a [electric] fan," recommends Mary Morrell, professor of sleep and respiratory physiology. "It will help move the air around your body and increase the chance of sweat evaporating." She recommends thin cotton sheets rather than nylon bedding. They will absorb sweat rather than leave the sleeper covered in a film of moisture. Insects are unlikely to bother people in cities, she believes. But for those in the countryside with the windows open, a mosquito net is one possible solution.
There's more to it than temperature and humidity, says Prof Kevin Morgan, director of the Clinical Sleep Research Unit. Hot days mean we get into bed in a different physical and mental state. "It's hot and you get into bed and don't get to sleep as quickly. The thing that stops you falling asleep is what you then start thinking about. Don't lie there thinking about why you didn't get that promotion. It's a recipe for mini insomnia." Catching up on sleep later in the day may be necessary for some. Instead, get up and read the paper or do something comforting as long as it doesn't involve turning on an email or computer.
A nightcap is not recommended unless it's something you do normally. "If you're used to having a couple of glasses of claret and that works for you, fine," Morgan says. "But don't have a toddy if you're not used to it. Alcohol is pretty good at putting you to sleep but pretty awful at keeping you asleep." Nor is a cold shower a good idea. "It will make you feel momentarily cold and close down the pores so you'll sweat less. If you have to shower, have a lukewarm one." The key thing is not to worry. Healthy humans can do with two poor nights' sleep in a row without any significant impact, Morgan says. "And by the third night you'll be so tired that you'll fall asleep quickly whatever the weather."
Important factors about Sleeping
"We have evolved to sleep in a consolidated way during the night, when it is cooler and darker. Too cold or too hot temperatures during the night act as a natural alarm clock.
"That late night cup of coffee or tea may have a noticeably greater effect on your ability to fall asleep. When it's hot, we naturally drink more liquids and that is because we need them. So don't go to bed thirsty, because the dehydration will wake you up even though the need to go to the bathroom doesn't.
"In Northern Europe, most of us have mechanisms in place to keep our homes warm during the winter, but not to keep them cool during the summer.
"As a species, we are diurnal," says Dr Malcolm von Schantz, a molecular neuroscientist at the University of Surrey's Sleep Centre.
"It can be a bit of a catch-22 situation - we need to open the window to let the cooler air in, but if we are reliant on blinds, this will also let the sun in before we would prefer to wake up. So getting curtains that keeps the light out and let the air through is a good start. Some people find sleeping with an electric fan hard to get used to, but a Japanese study has shown that using a fan during a hot night will decrease our time awake in bed by lowering the body temperature.
"Our warmest summer nights can be a bit of a double whammy for our sleep, because we get exposed both to too much heat and too much light. So what can we do?