Suffering a head injury can increase the chance of dying over the next 13 years regardless of its severity, research suggests.

People who are admitted to hospital for a head injury are twice as likely to die over the next decade or so as the general population living in the community.

Some 40% of people admitted to hospital died from a variety of causes over 13 years compared with 19% of people in the community and 28% of those admitted to hospital with other injuries, a study found.

Overall, more than 760 people with head injury were examined and compared with similar-sized groups.

Among the head injury group, the death rate was found to be "much higher" than for in people living in the community, according to the study in the Journal of Neurology, Neurosurgery and Psychiatry.

And the risk seemed to be significantly more for younger adults compared with older age groups.

The authors, from the universities of Edinburgh and Glasgow, said: "More than one year after injury, the death rate in younger (15 to 54 years) adults was much higher than in community controls (17.36 vs 2.36 per 1,000 per year) whereas in older adults the difference was more marginal (61.47 vs 42.36)."

The death rate appeared to stay higher regardless of whether the head injury was mild or more severe.

The researchers concluded: "Head injury is associated with increased vulnerability to death from a variety of causes for at least 13 years after hospital admission.

"There is a need to understand how head injury influences mortality, particularly in younger adults and after mild head injury."

Head injury accounts for most deaths from trauma in young adults.

While the risk of dying is already known to be higher in the first year after injury, this is the first time researchers have tried to conduct a robust study into the longer-term risks.

People in the study died from a variety of causes, including major reasons such as heart disease, respiratory disease, digestive disorders and cancers.

Lifestyle factors before the injury, such as excessive alcohol intake and living alone or a history of mental health problems did not influence the results.

Tom McMillan, professor of clinical neuropsychology from the University of Glasgow, who led the study, said: "While on the surface the figures are alarming, I would not want to unduly concern the public.

"There are no obvious explanations for the higher death rates among the young and middle aged, so further study is needed into this pattern.

"In addition, the number of people in the study is relatively low. It would be more concerning if this pattern were repeated in a far larger sample from a range of places across the world.

"This study throws up interesting questions that do deserve to be looked at further, but I would urge anyone who has suffered with a head injury not to be overly concerned by the findings."