Sleeping with a light on could be bad for you. Researchers from Tulane University in the USA say any kind of light at bedtime could be bad for your heart. Even a very dim light could be harmful. The researchers did tests on 11,000 people for a week. The test participants wore sensors that measured the amount of light in their bedrooms. People who did not have heart disease had an MRI scan three years later. The scans showed there was a link between sleeping with a light on and changes in the structure of the heart. One change was thicker heart muscles. Another change was that people's hearts were less able to pump blood, stretch, and relax during heartbeats.

The study is published in the European Heart Journal. Lead researcher Professor Lu Qi wrote: "Light pollution has emerged as a new risk factor for cardiovascular disease." He added the findings from his study suggest that reducing light while sleeping could be "one of the potential strategies for preventing heart disease". The researchers suggested turning off lights, televisions, and smartphones in the bedroom. They said people needed to get their sleeping environment as dark as possible. They added: "The advice is simple and inexpensive: blackout curtains, warm-coloured bedside lighting, and covering the small standby LEDs on household electronics."