Stressed people may be more likely to get killer infections because it weakens their immune system, scientists say.
A study of more than 1.7million people found twice as many PTSD patients suffered potentially deadly bugs than the general population.
Researchers also found patients with stress-related disorders, such as those immediately after bereavement or a car accident, for example, faced a similar heightened risk.
Evidence suggests stress may raise susceptibility to infections due to inflammation or raging hormones dampening key immune cells.
PTSD patients may be more likely to catch life-threatening infections such as meningitis, a study is found. Soldiers have higher rates of the stress related disorder
PTSD is estimated to affect around one in every three people who have a traumatic experience, such as rape or a car crash.
Overall, the condition is estimated to affect up to ten per cent of people, according to charities.
Soldiers, police, fire brigade or ambulance workers face a greater risk because they often have to deal with horrifying scenes.
University of Iceland researchers found a link between stress related disorders and risk of cardiovascular disease earlier this year.
But this is one of the first studies to draw data from a large group of people to assess the risk of life-threatening infections, published in the British Medical Journal.
Academics from the same university, as well as teams in the US, China and Sweden, used data from nearly 145,000 patients with PTSD or a stress-related disorder.
Stress-related disorders included acute stress reaction, which can occur immediately after a traumatic events and sometimes precedes PTSD.
Dr Huan Song and colleagues compared the participants with data taken from their unaffected siblings – a group of 180,000 people.
They also pooled data from a further 1,449,190 unaffected individuals in the general population. Participants were tracked for eight years, on average.
Infections studied included sepsis, meningitis and endocarditis – an infection of the inner lining of the heart.
Some 2.9 cases of life-threatening infections were diagnosed every 1,000 person years in patients with a stress-related disorder.
This figure was double the 1.3 in the general population and much higher than the 1.7 in their unaffected siblings.
The incidence of those with PTSD specifically was 2.9, compared to 1.2 in the general population and 1.6 in siblings.
Those with any stress related disorder had an 89 per cent higher risk of endocarditis than the general population.
They also had a 70 and 61 per cent higher risk of meningitis and sepsis – which is not an infection, but the body’s aggressive response to an infection.
Compared with their siblings, they had a 63 per cent higher risk of meningitis, 57 per cent higher risk of endocarditis and 52 per cent higher risk of sepsis.
Those with PTSD had up to a 95 per cent higher risk of a life-threatening condition than the population and their siblings.
The younger a patient was at diagnosis, the more likely they were to be to face such an infection.
Other mental health problems, especially substance use disorders, further increases the risk, the researchers said.
The excess risks discovered remained even when factors such as income, family background and other physical conditions were accounted for.
The true nature of the relation between physical health and stress related disorders is not understood.
One possibility is that stress heightens the level of glucocorticoids, hormones which naturally suppress the immune system.
This could make stressed individuals more vulnerable to catching an infection.
A more recent theory suggests stress causes a surge in inflammatory cytokines. An imbalance may result, exacerbating future infections.
The study, published in the journal ADD NAME OF JOURNAL HERE, is observational and cannot establish cause.
The researchers are unable to rule out the possibility that other unmeasured factors, such as smoking, may have influenced their results.