Perhaps you're just in the market for some new friends.

London - We are often told it is good to make new friends - but a study shows that our old ones end up paying the price.

Research reveals that there is a natural limit to the number of people we can stay in touch with. So when we form fresh bonds by starting a new job or going to university, we naturally demote or even drop older friends.

Even in today’s world when mobiles, email and social networks such as Facebook make it easy to stay in contact with a large number of people, the study shows we spend most of our time speaking to a limited amount of close friends and relatives.

And although our close friends may change, the number stays roughly the same. According to British and Finnish research published in the journal Proceedings of the National Academy of Sciences, we only have the brainpower to invest emotionally in a limited number of people.

An Oxford University researcher asked 24 students in their final months of school to list their friends and relatives and say how close to them they were. They were also given free mobiles and agreed to let researchers see their phone bills to work out who they called and for how long.

The study showed that as they moved on from school, they had roughly the same amount of close friends, it was just new ones replaced childhood friends.