Image caption The study only looked at women, not men

Mid-life stress may increase a woman's risk of developing dementia, according to researchers.

In a study of 800 Swedish women, those who had to cope with events such as divorce or bereavement were more likely to get Alzheimer's decades later.

The more stressful events there were, the higher the dementia risk became, BMJ Open reports.

The study authors say stress hormones may be to blame, triggering harmful alterations in the brain.

Stress hormones can cause a number of changes in the body and affect things such as blood pressure and blood sugar control.

Current evidence suggest the best ways to reduce the risk of dementia are to eat a balanced diet, take regular exercise, not smoke, and keep blood pressure and cholesterol in check Dr Simon Ridley , Alzheimer's Research UK

And they can remain at high levels many years after experiencing a traumatic event, Dr Lena Johansson and colleagues explain.

But they say more work is needed to confirm their findings and ascertain whether the same stress and dementia link might also occur in men.

Stress link

In the study, the women underwent a battery of tests and examinations when they were in either their late 30s, mid-40s or 50s, and then again at regular intervals over the next four decades.

At the start of the study, one in four women said they had experienced at least one stressful event, such as widowhood or unemployment.

A similar proportion had experienced at least two stressful events, while one in five had experienced at least three. The remaining women had either experienced more than this or none.

During follow-up, 425 of the women died and 153 developed dementia.

When the researchers looked back at the women's history of mid-life stress, they found the link between stress and dementia risk.

Dr Johansson says future studies should look at whether stress management and behavioural therapy might help offset dementia.

Dr Simon Ridley, of Alzheimer's Research UK, said that from this study, it was hard to know whether stress contributed directly to the development of dementia, whether it was purely an indicator of another underlying risk factor in this population of women, or whether the link was due to an entirely different factor.

"We know that the risk factors for dementia are complex and our age, genetics and environment may all play a role. Current evidence suggests the best ways to reduce the risk of dementia are to eat a balanced diet, take regular exercise, not smoke, and keep blood pressure and cholesterol in check.

"If you are feeling stressed or concerned about your health in general, we would recommend you talk this through with your GP."