Sleeping less than 8 hours a night is linked to intrusive and repetitive thoughts like those seen in anxiety and depression, reports a new study.

American researchers have studied the sleep duration of people with moderate to high levels of repetitive negative thinking.

We already know that that getting thoughts stuck in our head before we drop off can have a significant impact on sleep quality. And now a study suggests that disrupted sleep can make it more difficult to put negative thoughts aside in daily life.

The researchers exposed the study's participants to different pictures intended to trigger an emotional response. Their attention was observed through their eye movement.

The researchers found that the participants who slept the least and took the longest time to fall asleep, had greater difficulty in shifting their attention away from negative information.

"While other people may be able to receive negative information and move on, the participants had trouble ignoring it," noted study author Professor Meredith Coles.

These findings suggest that sleep disruption can affect the cognitive ability required to shift our attention away from negative stimuli.

In the medium to long term, these obsessive negative thoughts can make us more vulnerable to various psychological disorders such as anxiety and depression.

The researchers intend to carry out further studies to work out how sleep cycle duration could be a contributory factor in psychological disorders.

Studying sleep cycles in this way could one day help to create effective strategies for the treatment of anxiety and depression, the study suggests.

The study was published in the Journal of Behavior Therapy and Experimental Psychiatry.