Symptoms that predict the onset of dementia 20 years from now

The work was published in The Lancet Psychiatry.

Mid-life depression has previously been considered a risk factor for dementia in old age. However, the new analysis shows that it is probably not "depression as a whole" that plays a key role, but a limited set of individual manifestations.

The authors identify six symptoms that, when present in middle age, were most strongly associated with a later diagnosis of dementia:

• loss of self-confidence;

• a feeling of being unable to cope with problems;

• lack of feelings of warmth and affection for others;

• constant nervousness and tension;

• dissatisfaction with how tasks are accomplished;

• difficulty concentrating.

According to the researchers, paying closer attention to these symptoms when treating depression in middle-aged patients could potentially help reduce the risk of dementia in the future - although the link requires further study.

How the study was conducted

Researchers analysed data from 5,811 participants in the UK long-term Whitehall II project. Symptoms of depression were assessed between 1997 and 1999, when all participants were dementia-free and aged 45-69 (mean age around 55). A questionnaire of 30 common depressive symptoms was used for assessment.

Participants' health was then tracked for 25 years using national health registries, recording dementia diagnoses until 2023. During the follow-up period, 10.1 per cent of participants developed dementia.

The analysis showed: people who were classified as depressed in middle age (reported five or more symptoms) had a 27% higher risk of dementia later in life. However, the researchers clarify that it was the six specific symptoms that accounted for this increased risk in people under 60.

They found the strongest associations for two signs: loss of self-confidence and difficulty in overcoming problems - each of which was associated with about a 50 per cent increased risk of dementia.

Why these particular symptoms might be important

The authors suggest that manifestations such as reduced confidence, feelings of helplessness and problems with concentration may lead to less social activity and reduced 'cognitive load' (mentally stimulating activities). This potentially affects cognitive reserve - the brain's ability to compensate for damage for longer and maintain normal thinking even when changes begin to occur.

Meanwhile, a number of other depressive symptoms - such as sleep disturbances, suicidal ideation or simply a lowered mood - showed no discernible association with dementia in the long term.

The researchers emphasise that more work is needed on other samples to test whether the results apply equally to different populations.