A new study has suggested that steadily increasing symptoms of depression in older age could indicate the first signs of dementia.
The research, published in the Lancet Psychiatry journal, found that other patterns of symptoms, such as chronic depression, were not linked to the condition.
Experts at the Erasmus University Medical Center in Rotterdam followed more than 3,000 adults living in the Netherlands.
All participants were aged 55 or older and had no symptoms of dementia at the start of the study. The research looked at different ways in which depression progressed over time and how this related to the risk of dementia.
The team calculated that worsening depression may indicate that the damage caused by the condition could have already started. Their findings also revealed that it was only the group whose symptoms of depression had increased over time that were found to be at an increased risk of dementia.
Overall, this meant that around a fifth of those involved in the research developed the condition. Others who had symptoms that were reduced or stayed the same over the study period were not at a higher risk, the study concluded.
For example, in those who experienced low but stable levels of depression, around 10% went on to develop dementia.
Dr M Arfan Ikram, assistant professor in Neuroepidemiology at the Erasmus University Medical Center, said depressive symptoms that gradually increase over time appear to be a better predictor of dementia later in life than other paths of depression.
"There are a number of potential explanations, including that depression and dementia may both be symptoms of a common underlying cause, or that increasing depressive symptoms are on the starting end of a dementia continuum in older adults," Dr Ikram explained.
Dr Simon Ridley, director of research at Alzheimer's Research UK, said anyone concerned about either depression or dementia should seek professional help.
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