Head injuries may be worryingly common among police officers, according to a new pilot study led by the University of Exeter.
In a sample of 54 UK officers, 21 (38.9%) reported having suffered a "traumatic brain injury" (TBI) resulting in a loss of consciousness in their lives.
This proportion is far higher than the estimated rate of 8-12% in the general public.
Officers with a history of TBI reported higher levels of ongoing "post-concussion symptoms" such as headaches, memory problems and anxiety.
These officers were also moderately more likely to report symptoms of post-traumatic stress disorder (PTSD) and drinking alcohol to cope, and much more likely to report symptoms of depression.
The pilot study is one of the first to examine this issue among police officers, and the researchers say more investigation is urgently needed.
"The main thing to take away from this is that we need to look after people who are in the front line of public protection," said Professor Huw Williams, of the University of Exeter.
"TBI has been extensively linked to mental health difficulties including PTSD, depression and alcohol abuse.
"Being a police officer is a dangerous job - with a risk of both physical and mental trauma - yet there has been a surprising lack of research investigating the presence and influence of TBI in the police.
"Our pilot study is based on a relatively small sample size, but it illustrates the importance of screening for TBI and offering treatment and support where necessary."
Professor Williams added: "Many police forces are moving towards a more sensitive, 'trauma-informed' approach to dealing with the public.
"We expect police officers to turn up in a variety of hideous situations, so it's vital that they are given then help they need to recover from and trauma - including brain injuries - that they suffer."
Interestingly, two thirds of the TBIs reported happened outside of police work.
The study does not explore the circumstances of these injuries, but the researchers say officers may be more likely than the public to engage in high-risk leisure activities, and some may have been injured in previous work such as military service.
All TBI cases in the study were classified as "mild" - with loss of consciousness of less than 30 minutes.
However, the authors noted that repeated TBI was common - a matter of "particular concern" as this is known to raise the risk of mental health issues.
"TBI, including mild forms, can cause significant and potentially long-lasting cognitive, emotional and behavioural impairments," said lead author Nick Smith, of the University of Exeter.
"This includes a three-fold increased risk of suicide in those suffering from any TBI.
"However, with the right support and treatment, it is possible to recover from TBI and avoid getting into negative coping mechanisms such as alcohol abuse.
"In other fields, such as sport, head injuries have received a great deal of attention, and protocols have improved dramatically.
"We need to take similar care of police officers."
Detective Chief Inspector Lewis Prescott-Mayling, a co-author of the paper, said: "We have some fantastic support for our staff but we need to treat people according to their needs and as early as possible.
"The trauma people are exposed to can have lasting effects.
"This applies to our staff as much as to people from our communities.
"We welcome this research and its findings."
Of the 54 officers in the study, nine met criteria for PTSD and 21 met criteria for mild or more severe depression.
The study - conducted in a UK police constabulary - suggests a surprising parallel with the UK prison population, as previous research has suggested about 60% of inmates have suffered a TBI.
The paper, published in the Journal of Psychiatric and Mental Health Nursing, is entitled: "A pilot study of brain injury in police officers: A source of mental health problems?"