Eight hours a day is a lot of time to trudge through if you don't like the people around you. For this obvious reason most people hope to make at least casual friendships at the office, but how close should these relationships be? And beyond entertaining you, do they actually impact your professional performance?

These are the sort of questions tackled by new research published in Personnel Psychology. The series of studies asked employees of a large insurance company, as well as several shops and a restaurant, to submit lists of both the colleagues they worked the most closely with and their closest work friends. The research team used this data to figure out which employees worked with their good friends and then compared the performance of employees with lots of work BFFs to that of their less sociable co-workers.

Work friendships boost performance...

The first half of the findings is good news for office social butterflies. The research revealed that having lots of good friends with whom you work closely tends to boost performance.

"This was explained in part by the fact that such relationships were associated with experiencing more positive work-related emotions, like feeling excited and proud. In short, being friends with more of colleagues appeared to be good for staff and for their employer," says the British Psychological Society Research Digest blog, summing up this portion of the findings.

... but also exhaust you.

But before you go inviting all and sundry out for every available happy hour, you should know that's not all the psychologists uncovered. Work friendships are, in fact, a "mixed blessing," they concluded. Having lots of work buddies makes you happier and more productive, but it also makes you tired.

Apparently, the more friendships you are juggling at work, the more likely you are to feel emotionally exhausted. This is "presumably because of the effort involved in maintaining more complex relationships and of providing support to friends," explains the BPS post.

Still, despite the emotional costs of helping out your work pals, overall the researchers concluded that when all the costs and benefits are weighed, the more quality relationships you can cultivate at work, the better. That's probably not going to come as a shock to anyone who has laughed their way through a tough workday with a great friend, but it might just reassure nervous managers who are concerned all those jokes are a distraction from the job at hand.