Enjoying good quality sleep is more important than sleeping for the recommended amount each night if you want to prevent illnesses, a new first-of-its-kind study suggests.
People who don't get 'quality sleep' or enough sleep are nearly three times as likely to suffer from colds, flu and other respiratory diseases like COVID-19, according to the new research.
But, distinguishing this, it also unearthed that how well you sleep can effectively make up for sleeping for less than the optimal number of hours, in terms of boosting your immune system and staving off viral infections.
Professor Neil Walsh of Liverpool John Moores University said his team's findings, as published in the journal Sleep, "change the way we should think about sleep and health".
"Sleep is important for mental and physical health, including our ability to fight infection," the lead researcher told the PA news agency. "The National Sleep Foundation recommends adults get seven-to-nine hours sleep each night."
While adults need seven to nine, children need nine to 13 and toddlers and babies need 12 to 17 hours, according to the NHS.
The health body explains you're probably not getting enough sleep if you're constantly tired during the day.
"Yet," added Professor Walsh, "many of us restrict our sleep to make way for our busy lives – for example, we regularly restrict our sleep when we get up early for our weekday commitments.
"But when you restrict your sleep, you are not necessarily going to be more likely to get sick – it really depends on your quality."
In the new study, the scientists followed 1,318 new military recruits for 12 weeks, tracking their sleep patterns and health in the weeks before training and after joining, where they had to follow strict wake-up routines.
On average, they were found to sleep two hours less during military training than in civilian life.
But nevertheless, the researches noted that more than half of those with restricted sleep still rated it as good quality.
Military recruits who reported sleep restriction during training were nearly three times as likely to suffer with respiratory infection, according to the team, taking into account factors that influence these illnesses, like the time of year and smoking.
However, they also found that sleep restriction only increased infection among those reporting poor sleep quality, while good sleep quality protected against respiratory illnesses, despite the shorter duration.
"There are two very key messages here: firstly that restricted sleep patterns can result in more frequent illness, and secondly and more surprisingly, that sleeping well can trump sleeping long in terms of our immunity to illness.
"That is an extremely useful message in our hectic world where sleep is often sacrificed for other pursuits."
If you regularly have problems sleeping, you might have insomnia, which means you may find it hard to fall asleep, wake up several times in the night, lie awake, wake up early, still feel tired after sleep, find it hard to nap, feel irritable during the day and find it difficult to concentrate.
How to improve sleep quality
Based on the study's findings, Professor Walsh said there are five things people can do to improve sleep quality:
Adopt a consistent sleep schedule (similar bed and wake up time, including weekends)
Avoid large meals, caffeine and alcohol close to bedtime
Ensure the bed and pillow are comfortable and the room is cool, dark and quiet
Establish a relaxing bedtime routine (go screen-free 40 mins before bedtime and going to bed when sleepy)
Exercise during the day to help fall asleep at night
The NHS suggests 'confronting sleepiness' too, which means not forcing yourself to sleep if you find yourself lying awake at night. Instead, get up and do something relaxing and return to bed when you feel more sleepy.
It also recommends writing down your worries if you're someone who lies awake worrying about tomorrow. Setting aside time before bed to make a list for the net day can help ease your mind.
If changing your sleeping habits hasn't helped, you have had trouble sleeping for months and your insomnia is affecting your daily life, see a GP.
Additional reporting PA.
Watch: COVID is still impacting our sleep habits, survey shows