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One in three adults sleeps in the nude, according to an international study by the U.S. National Sleep Foundation, and it�s been shown to have all sorts of benefits. Here, experts reveal how ditching pyjamas could improve your sleep quality, boost your relationship and may even help burn calories. Sleep experts agree it�s important to keep cool at night as your body (or �core�) temperature needs to drop by about half a degree for you to fall asleep. The brain, driven by your internal body clock, sends messages to the blood vessels to open up and release heat. �Your core temperature is at its highest at 11pm and its lowest at 4am,� says Dr Chris Idzikowski, director of the Edinburgh Sleep Centre and author of Sound Asleep: The Expert Guide To Sleeping Well. �If anything prevents that decline in temperature, the brain will wake itself up to see what�s going on, meaning you�ll struggle to get to sleep or you�ll have disturbed sleep. �The advantage of sleeping naked is it�s easier for the body to cool and maintain the lower temperature the brain wants to achieve.� Russell Foster, professor of circadian neuroscience at the University of Oxford, says ditching nightwear may improve your slumber. �If you�re wearing lots of bedclothes it�s going to be more difficult to regulate your temperature, so wear the least you can get away with.� Disrupted sleep from being too hot doesn�t just mean you�ll get less sleep overall, but it might mean less deep sleep, the most restorative type. Deep sleep is key for memory consolidation and the production of growth hormone � important for cell repair and growth. Why does the body cool down during sleep? One theory is that it evolved to do this because our ancestors in Africa would grab some rest in the afternoon, and needed to keep cool in the savanna heat. There is an increasing focus on brown fat, a type of tissue in the body that may protect against weight gain. While ordinary body fat piles on when we eat more calories than we burn, brown fat seems to burn excess calories to generate heat. We know babies have lots of brown fat � they need it to keep warm � but studies have shown there are small amounts in the necks of adults, too. Experts believe that certain activities could switch on this fat, potentially helping to burn calories at a greater rate. In a U.S. study in the journal Diabetes, researchers found that sleeping in a cold bedroom could activate brown fat in adults. Five healthy young men slept in climate-controlled bedrooms for four months. For the first month, the room was kept at 24�C, then it was lowered to 19�C, then it went back to 24�C and for the last month raised to 27�C. They ate the same amount of calories and their calorie expenditure and insulin sensitivity � how much insulin the body needs to keep blood sugar levels stable � were measured each day. The results were striking. After four weeks sleeping at 19�C, the men had almost doubled their volumes of brown fat.