Stressful life experiences can age the brain by several years, new research suggests.
Experts led by a team from the University of Wisconsin School of Medicine and Public Health in the US found that even one major stressful event early in life may have an impact on later brain health.
The team examined data for 1,320 people who reported stressful experiences over their lifetime and underwent tests in areas such as thinking and memory.
People were aged 58 on average and included 1,232 whites and 82 African Americans.
A series of neuropsychological tests examined several areas including four memory scores (immediate memory, verbal learning and memory, visual learning and memory, and story recall).
Stressful life experiences included things such as losing a job, the death of a child, divorce or growing up with a parent who abused alcohol or drugs.
The results showed that a larger number of stressful events was linked to poorer cognitive function in later life.
When looking specifically at African Americans, the team found they experienced over 60% more stressful events than white people during their lifetimes.
Researchers said that, in African Americans, each stressful experience was equivalent to approximately four years of cognitive ageing.
The study, which has not been published in a peer-reviewed journal, was presented at the Alzheimer's Association International Conference in London.
Dr Maria Carrillo, chief science officer for the Alzheimer's Association, said: "The stressful events that the researchers were focusing on were a large variety ... the death of a parent, abuse, loss of a job, loss of a home... poverty, living in a disadvantaged neighbourhood, divorce."
She said that even a change of school could be regarded as a stressful life event for some children.
Dr Doug Brown, director of research and development at the Alzheimer's Society, said: "We know that prolonged stress can have an impact on our health, so it's no surprise that this study indicates stressful life events may also affect our memory and thinking abilities later in life.
"However, it remains to be established whether these stressful life events can lead to an increased risk of dementia.
"Studying the role of stress is complex.
"It is hard to separate from other conditions such as anxiety and depression, which are also thought to contribute towards dementia risk.
"However, the findings do indicate that more should be done to support people from disadvantaged communities that are more likely to experience stressful life events.
"As we improve our understanding of risk factors for dementia, it is increasingly important to establish the role that stress and stressful life events play.
"To unravel this, more research is needed over a longer time scale. If you are experiencing stress or worried about your health, it's important to visit your GP."
Other research has suggested there are plausible links between stress and chronic inflammation, which in turn may accelerate the development of dementia.
But experts believe that a health lifestyle and a healthy diet can help mitigate this risk, even for those people going through stressful events.