More time spent on Facebook has been associated with less time spent on physical fitness, say researchers.
The study also found that fans of Facebook were less likely to play team sports, the New York Daily News reported.
The study found that the more time you spend on Facebook, Twitter, and other social media sites, the less active you are and more susceptible you are to packing on extra pounds.
Most students used social networking sites for an average of one hour each day.
Slightly more than half of the students rated themselves as "moderately active," one-third of the subjects said they were "highly active," and 12.7 percent reported "low physical activity."
Of the students involved in the study, only 25 percent said they participated in team sports, the report said.
"Time is a finite resource, so time spent in social networking must come at the expense of other activities," lead author Dr. Wendy Cousins, a psychologist at the University of Ulster, said.
"Our study suggests that physical activity may be one of those activities," Cousins said.
The study was presented at the annual conference of the British Psychological Society's Division of Health Psychology in Liverpool this week.