Feeling moody or depressed? Too much light in your bedroom at night could be to blame, say scientists. Exposure to even the dimmest light while you're asleep - such as a night light, street lighting or the glow of a TV screen - could be enough to affect your brain.
The researchers from Ohio State University have just presented their findings at the annual meeting of the American Society for Neuroscientists. Admittedly their tests were carried out on hamsters, but the results could be significant for humans too, they claim.
It's all linked to a hormone called melatonin, which your brain produces when it's dark to prepare your body for sleep. But even the slightest amount of light interferes with melatonin production, the scientists claim.
After eight weeks of tests they discovered changes in the brains of the hamsters who were exposed to dim light at night, specifically changes in a part of the brain called the hippocampus. Earlier studies suggest the hippocampus is involved in depression - for instance, the hippocampus is smaller in depressed people than in those who aren't depressed.
So the scientists decided to check by giving the hamsters sugar water to drink - a real treat for a hamster, apparently. The hamsters that had been exposed to light at night had lost their taste for sugar water, which suggests a loss of enjoyment (a major symptom of depression called anhedonia).
The reason for the changes in the hippocampus isn't clear, but it appears to have something to do with the reduced production of melatonin, say the researchers.
If you're having problems sleeping, there are natural remedies for insomnia you could try.