Sleep in numbers
• Two-thirds of adults in developed nations fail to obtain the nightly eight hours of sleep recommended by the World Health Organisation.
• An adult sleeping only 6.75 hours a night would be predicted to live only to their early 60s without medical intervention.
• A 2013 study reported that men who slept too little had a sperm count 29% lower than those who regularly get a full and restful night’s sleep.
• The time taken to reach physical exhaustion by athletes who obtain anything less than eight hours of sleep, and especially less than six hours, drops by 10-30%.
• If you drive a car when you have had less than five hours’ sleep, you are 4.3 times more likely to be involved in a crash. If you drive having had four hours, you are 11.5 times more likely to be involved in an accident.
• A hot bath aids sleep not because it makes you warm, but because your dilated blood vessels radiate inner heat, and your core body temperature drops. To successfully initiate sleep, your core temperature needs to drop about 1C.
• There are now more than 100 diagnosed sleep disorders, of which insomnia is the most common.
• Morning types, who prefer to awake at or around dawn, make up about 40% of the population. Evening types, who prefer to go to bed late and wake up late, account for about 30%. The remaining 30% lie somewhere in between.