We wrote an earlier article about the advantages of cotton onesie sleepwear. Various research in to sleep quality backs up the importance of body temperature in creating the right conditions for quality sleep. Dr Chris Idzikowski, director of the Edinburgh Sleep Centre and author of Sound Asleep: The Expert Guide To Sleeping Well agrees that it’s important to keep cool at night as body (or “core”) temperature needs to drop by about half a degree for you to fall asleep. The human brain 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, “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.” As cotton is a breathable, natural fabric it will not interfere with sleep patterns. We need periods of deep restorative sleep for memory consolidation and the production of growth hormone – important for cell repair and growth.
Although allowing the body to cool is important, make sure you have warm hands and feet. For your temperature to lower to the level that triggers sound sleep, your body needs to lose excess heat by sending blood to the vessels on the hands and feet – where heat is lost through the skin surface. People with Raynaud’s syndrome – a common condition characterised by very cold hands and feet (thought to affect up to ten million people in the UK) are more likely to suffer with insomnia. The condition causes the blood vessels in the extremities to spasm, reducing blood flow, so though sufferers’ hands and feet may feel very cold, their core temperature is too high.
Research at the Dutch Institute of Neuroscience has reinforced the importance of body temperature in sleep. In a study, volunteers slept wearing special suits that allowed researchers to manipulate their skin temperature without altering core temperature. They found that overall when skin temperature was raised by just 0.4c, the volunteers were significantly less likely to wake in the night. And in the elderly volunteers, the effect was greater as the 0.4c rise almost doubled the proportion of deep sleep and decreased the risk of waking too early from 50 percent to four percent.
Warming the skin caused blood vessels in the extremities to widen, so heat could be lost more easily. In other words, to fall asleep easily, you need to be warm enough that your blood vessels won’t constrict, but not so hot that your body can’t cool down.
So if you are buying a onesie for sleeping in, choose cotton onesie sleepwear. For something to keep you extra warm around the house, fleece onesies are best.