Stressful events in life, including divorce or the death of a parent, can age the brain by several years, new research suggests.
Experts in the US found that even one major stressful event early in life may have an impact on later brain health.
The team from the University of Wisconsin School of Medicine and Public Health examined data for 1,320 people who reported stressful experiences over their lifetime and underwent neuropsychological tests.
The tests examined several areas including four memory scores - immediate memory; verbal learning and memory; visual learning and memory; and story recall.
Those taking part were aged 58 on average and included 1,232 whites and 82 African Americans.
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 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.
But he said it had not been established whether stressful life events can increase the risk of dementia.
"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." he said.