Long-term stress may cause illness by prematurely ageing the immune system, research suggests.
Stress can cause long-term damage
Scientists have discovered stressful experiences can boost production of chemicals that regulate the body's immune system.
One of these, interleukin 6 (IL-6), naturally increases with age, and is linked to heart disease, type 2 diabetes, osteoporosis and other age-related conditions.
A team led by Dr Ronald Glaser, from Ohio State University College of Medicine in Columbus, US, measured levels of this chemical in 119 older men and women who were caring for a spouse with dementia.
Over six years, levels of the chemical increased four times faster in the carers compared with 106 people not providing care.
Former carers continued to have elevated IL-6 for up to three years after the death of the spouse they were looking after.
Previous research has shown carers are generally iller and have a poorer immune response to influenza than the rest of the population.
They also have elevated blood pressure, and their wounds heal slowly.
Writing in the journal Proceedings of the National Academy of Sciences, the researchers said: "These data provide importance evidence of a key mechanism through which
chronic stressors may have potent health consequences for older adults, accelerating risk of a host of age-related diseases."
Professor Stephen Bloom, a stress expert from Imperial College, London, told BBC News Online there was a lot of evidence to show stress increased the incidence of illness.
"After the death of a spouse the surviving partner has a shortened life expectancy, and an increased chance of dying in the six months after bereavement.
"This is almost certainly because of stress," he said.
"And children who are exposed to stress stop growing almost entirely."
Professor Bloom said the stress response was deep seated reaction designed to prepare the body for physical conflict, or to run away from danger.
"When the emergency "flight or fight" response kicks other systems within the body tend to get put on the back burner," he said.
Professor Jane Gilliard is director of Dementia Voice - the Dementia Services Development Centre in the South West of England.
She said: "Hopefully, the findings will raise awareness amongst care professionals, and particularly GPs, about the impact that caring for someone with dementia can have on all aspects of the lives of those who care."