Time spent on social networking sites comes at the expense of other activities -- including physical activity, new research by the University of Ulster has revealed.

That is one of the findings of a study presented at the annual conference of the British Psychological Society's Division of Health Psychology in Liverpool at the weekend.

Around 350 students at the University of Ulster completed an online survey -measuring social networking activity and levels of physical activity.

The research was carried out by Masters degree student Emer O'Leary, under the supervision of psychologists, Dr Wendy Cousins and Dr Tadhg Macintyre at the University of Ulster.

The results showed that the vast majority of students used social networking sites like Facebook and Twitter spend an average of one hour a day online. In the physical activity questionnaire, just over half the students were classified as; 'moderately active' and a third were 'high activity', with a minority (12.7 per cent) falling into the 'low physical activity' group. A quarter of the respondents said they took part in team sports.

When the results were analysed, researchers found that the amount of time spent on social network websites was negatively correlated with the respondents' level of physical activity in the previous week. Facebook fans were also less likely to take part in team sports, but this effect was less pronounced.

Dr Cousins said: "Time is a finite resource, so time spent in social networking must come at the expense of other activities. Our study suggests that physical activity may be one of those activities.

"Our findings are intriguing, but we have not conclusively demonstrated that social networking causes lower levels of physical activity. We will need to carry out more research to see if it really is a case of Facebook makes you fat rather than Twitter makes you fitter."