People who suffer from depression could be at a much greater risk of developing dementia later in life, a study has revealed.

Depression can significantly increase the chances of developing Alzheimer’s disease or other forms of dementia later in life, the research suggests.

The findings, from a US study, reinforce a perceived connection between depression and Alzheimer’s, and other forms of dementia.

Scientists have yet to discover what causes the link but have pointed to brain inflammation, the action of certain proteins, and lifestyle factors as possible drivers.

The latest research involved almost 1,000 people with an average age of 79 who had been enrolled into a large US heart study.

At the beginning, all were free of dementia. Psychological tests identified that 125, or 13%, of the study participants, were classified as being depressed.

By the end of the 17-year study, 164 of the recruits had dementia, of whom 136 were diagnosed with Alzheimer’s.

Nearly 22% of those who were depressed at the outset developed dementia compared with 16.6% of those free from depression. They were around 30% more likely to acquire a dementia illness.

Leading researcher Dr Jane Saczynski, from the University of Massachusetts Medical School in Worcester, US, said: “Inflammation of brain tissue that occurs when a person is depressed might contribute to dementia. Certain proteins found in the brain that increase with depression may also increase the risk of developing dementia.”

The results, published in the journal Neurology, were unaffected by a person’s age, sex, education, or possession of the defective APOE gene that is known to increase the risk of Alzheimer’s disease.