The death of a close friend has a much longer lasting impact than previously believed, a new study has found.

Previous studies have suggested that the grieving period for a close friend lasts around 12 months. However, researchers in Australia have found that the death of a close friend can affect a person's physical, psychological and social wellbeing for up to four years - four times longer than previously thought.

The researchers looked at more than 26,000 people, over 9,500 of whom had experienced the death of at least one close friend.

They found that those grieving the loss of a close friend experienced a major decline in physical health, mental health, emotional stability and their social life.

"We all know that when someone loses a partner, parent or child, that person is likely to suffer through a significant grieving period. Yet death of a close friend, which most of us will experience, is not afforded the same level of seriousness by employers, doctors, and the community.

"The death of a friend is a form of disenfranchised grief - one not taken so seriously or afforded such significance," commented the study's lead author, Dr Wai-Man (Raymond) Liu of the Australian National University.

He said that as a result, people are being left without the supports and services they need ‘during a very traumatic period of their lives'.

The researchers are calling on doctors and policy makers to reconsider the way that they approach people who have experienced the loss of a close friend.

"We need to recognise the death of a close friend takes a serious toll, and to offer health and psychological services to assist these people over an adequate period of time," Dr Liu added.

Details of these findings are published in the journal, PLOS (Public Library of Science) One.