An almost 40 year study in Sweden, involving 800 women, found that women who had experienced stressful events in middle age, were more likely to develop dementia as they grew older.

Such events include divorce, widowhood or alcohol abuse in a spouse or close relative.

Dr, Simon Ridley of Alzheimer’s Research UK, says hormone levels can also trigger 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.

The results are published in the British Medical Journal.