Everyone knows that good sleep is important for our health. Not everyone knows how important it is to sleep in the dark. A new report says sleeping with the light on could be bad for our health. Researchers say turning off the light when we sleep helps to keep away diabetes and heart disease. Sleeping with the light on could increase the risk of getting these diseases. The researchers said around 40 per cent of people sleep with some sort of artificial light. They said even light from a television or alarm clock could affect our health. They added that the worst thing to sleep with is a main light. Sleeping in the dark is more difficult for people who live in cities, where there is a lot of outdoor light at night.

The researchers are from the Northwestern University Feinberg School of Medicine in Chicago, USA. The lead researcher, Dr Phyllis Zee, is an expert in sleep medicine. She said it is healthier for us to turn off all lights when we sleep. Her team conducted a study of the blood sugar levels of 20 people after nights of sleep. The people who slept with a light on had higher blood sugar levels the next morning compared to those who slept in total darkness. Dr Zee said this is because light stimulates brain activity, which raises blood sugar levels. She said there are three things we can do to reduce the risk of illness: turn off the lights, never sleep with white or blue light; and use a blackout curtain or wear an eye mask.