The more 'friends' you have on Facebook, the more likely you are to feel stressed, says a new study.

Psychologists believe that those who are most addicted to the website can develop 'Facebook-related anxiety'.

The negative effects of using the site, which has more than 500 million members, outweighed the benefits of staying in touch with friends and family, the Daily Mail reports. Researchers from Edinburgh Napier University questioned students on their use of the site.

Many said turning down friend requests left them feeling guilty, while more than one in ten found just being on the site a 'nervous' experience.