The science behind why we struggle to sleep in the heat

If you can't sleep during hot, muggy nights it's probably because your core body temperature is unable to drop to where ...

If you can't sleep during hot, muggy nights it's probably because your core body temperature is unable to drop to where it needs to be.

A string of hot and muggy nights have robbed Kiwis of their precious beauty sleep during the past week.

Several regions have been breaking through the 30 degrees Celsius barrier in the last few days, while in Kaikoura it was already 21C by 6am on Tuesday.

Some people struggling with the heat in Auckland took to sleeping with ice-cold water bottles and making DIY swimming pools, while others stripped down to their undies.

If temperatures in your bedroom climb above 25C you're unlikely to get a good sleep.
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If temperatures in your bedroom climb above 25C you're unlikely to get a good sleep.

So, what is it that makes it so hard to get some decent shut-eye in these conditions?

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If you don't get a good sleep you're likely to be irritable and you'll struggle to concentrate.
123RF

If you don't get a good sleep you're likely to be irritable and you'll struggle to concentrate.

WHY DOES THE HEAT INTERRUPT YOUR SLEEP?

Sleep expert Dr Alex Bartle says the issue of nodding off during hot, muggy nights is a topical one at the moment, "for obvious reasons".

Basically, it all comes down to melatonin.

This magic hormone helps regulate the sleep cycle by dropping your core body temperature. It is mainly produced between 10pm and 5am.

However, that process is interrupted when your body temperature is too high.

The body is unable to produce the melatonin needed and your core body temperature can't drop to the necessary level.

Sleep-Wake Research Centre fellow Karyn O'Keefe says high humidity can exacerbate the effects of a hot room.

"When it is too hot, it is difficult for us to cool our bodies which can interrupt the relaxation process and make it difficult for us to fall asleep," O'Keefe says.

Hot nights mean an increase in how long it takes to get to sleep, how long it takes to get into a deep sleep, and the number of times you'll wake during the night, she says.

HOW HOT IS TOO HOT?

A hot night can make it take longer to get to sleep, longer to get into a deep sleep and is likely to increase the ...

A hot night can make it take longer to get to sleep, longer to get into a deep sleep and is likely to increase the number of times you wake during the night.

Ideally, your bedroom should be between 16C and 18C, Bartle says.

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If temperatures climb over 22C, you're going to have trouble sleeping.

O'Keefe says most people's sleep will be disrupted when the temperature climbs above 25C.

Even if the temperature has dropped outside, it's common for bedrooms to reach up to 30C at night during the summer months.

Bartle suggests closing up the bedroom (windows, curtains and doors) while it's cool in the morning to stop it heating up during the day, and opening windows and doors at night to increase airflow.

Other tips include using aircon, a fan, a dehumidifier or placing a bowl of ice in front of a fan as a sort of DIY aircon.

WHAT ABOUT THE KIDS?

Bartle says it's important to be mindful of children getting too hot at night.

The temperature in a child's room shouldn't be any warmer than 19C, he says.

Parents should be careful not to tuck children in too tight during the summer.

And if they climb out of the bed clothes, leave them be.

WHAT IF YOU DO GET A BAD SLEEP?

So your room got too hot last night, what does that mean for work today?

Bartle says a bad night's sleep is likely to affect your mood and thinking the next day.

In 2015, an international panel of experts finally reached a consensus on how much sleep we need - they settled on seven to nine hours a night.

If you get any less you are likely to struggle to concentrate, you won't be able to consolidate memories, your speed of thinking will slow down, your decision making will suffer, and you're likely to be irritable.

Bartle says children who don't get enough sleep often display behaviour similar to that of a child with ADHD.

O'Keefe says a bad night's sleep also affects reaction times and coordination, which can have implications for driving.

WHAT DOES THIS MEAN FOR PEOPLE IN TROPICAL COUNTRIES?

People who deal with hot or muggy conditions throughout the year have adjusted their way of life to make sure they get a good sleep.

Bartle says houses in such countries often had less enclosed spaces, which made for better airflow.

Buildings that don't have air conditioning usually have ceiling fans, and if there aren't any fans, any doors or windows stay open at night.

Tropical locals also tend to sleep in light clothing without bedding.

O'Keefe says people can adapt their thermoregulatory systems to different climates, so people living in hotter places are still able to get a good sleep as long as they can cool their core body temperature at night.

 - Stuff

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