A recent study published in the International Journal of Geriatric Psychiatry reveals a significant link between depression and an increased risk of developing dementia. Conducted over 15 years, the study found that people with depression at the start of the study were 74% more likely to develop dementia than those without depression. Additionally, the onset of dementia occurred about two years earlier in individuals with depression. These findings underscore the importance of early detection and treatment of depression to potentially prevent future cognitive decline.
The global population is aging rapidly, with the number of people aged 65 and older projected to double from 703 million in 2019 to 1.5 billion by 2050. This demographic shift is expected to lead to a significant increase in the number of people with dementia, from 47.5 million in 2015 to an estimated 135.46 million by 2050. With approximately 7.7 million new cases of dementia anticipated each year, understanding and mitigating risk factors for dementia has become a public health priority.
Dementia is a general term for a decline in cognitive function severe enough to interfere with daily life. It encompasses a range of symptoms, including memory loss, difficulty with problem-solving, language issues, and impaired reasoning and judgment.
Dementia is caused by damage to brain cells and can result from various diseases or conditions, with Alzheimer’s disease being the most common cause. While it primarily affects older adults, it is not a normal part of aging.
Previous research has suggested a possible link between depression and dementia, but the exact nature of this relationship has been debated. Some studies suggest that depression could be an early symptom of dementia, while others propose that it might be a risk factor or a complication of dementia. The current study aimed to clarify this relationship by examining whether depression at baseline increases the risk of developing dementia over a long-term follow-up period.
“I have been a geriatrician for about 10 years. I believe that to confirm in a large population study that depression could be a risk factor for dementia and mild cognitive impairment is of importance,” said study author Nicola Veronese, an associate professor at the University of Palermo.
“Depression, in fact, differently from dementia, is a condition sensitive to pharmacological and non-pharmacological treatments. I hope that our study encourages further research in checking if to reverse depression is able to decrease the risk of dementia.”
The study utilized data from the Survey of Health, Aging and Retirement in Europe (SHARE), a large, multidisciplinary, cross-national panel study. The SHARE study includes a representative sample of individuals aged 50 and older from 27 European countries and Israel. The data was collected through multiple waves of the survey, beginning between 2004 and 2006 and continuing until 2019/2020.
Participants were assessed for depressive symptoms using the EURO-D scale, a 12-item questionnaire that measures various aspects of depression, including pessimism, sleep quality, and concentration. A score of 4 or higher on the EURO-D scale was indicative of depression.
The onset of dementia was determined through self-reports or reports from caregivers or family members, who were asked whether a doctor had diagnosed the participant with Alzheimer’s disease, dementia, or senility. Cognitive impairment was assessed using a combination of memory recall and verbal fluency tasks, with participants who performed significantly below age-graded norms being classified as cognitively impaired.
Among the 22,789 participants included in the study, 24.9% were identified as having depression at baseline. These participants were generally older, more likely to be female, less likely to be married or educated, and had higher rates of chronic diseases and limitations in daily activities.
Over the 15-year follow-up period, 1,419 participants developed dementia, corresponding to an incidence rate of 7.31 per 1,000 person-years. The study found that the presence of depression at baseline significantly increased the risk of dementia by 74%. This association was particularly strong in younger participants, with those under 60 years old being twice as likely to develop dementia if they had depression.
“The main take-home message is that depression has cognitive aspects that must be considered every time that we approach a person affected by this condition,” Veronese told PsyPost.
Interestingly, the study also found that specific symptoms of depression, such as loss of concentration, were strong predictors of dementia. Other symptoms, like pessimism and fatigue, were also associated with an increased risk, while poor sleep was not.
“I was surprised that not only depression, but also specific items of the tool used for the detection of depression may predict the onset of dementia,” Veronese said.
Despite its large sample size and long follow-up period, the study has some limitations. Firstly, the assessment of depression was based on self-reported symptoms rather than clinical diagnoses, which could introduce bias. Similarly, the diagnosis of dementia was also self-reported, which might not capture all cases accurately. The study did not distinguish between different types of dementia, which could have different risk profiles related to depression.
“The SHARE study was not designed to specifically explore the relationship between depression and dementia: their diagnoses are only based on tools or self-reported information that can introduce a bias in our findings,” Veronese explained.
Another limitation is the potential for reverse causation, where early symptoms of dementia could be mistaken for depression. Although the study attempted to address this by excluding cases of dementia diagnosed within the first five years of follow-up, this remains a possibility.
Future research should focus on confirming these findings in other populations and exploring whether treating depression can reduce the risk of dementia, Veronese said. Studies could also aim to identify the biological mechanisms linking depression and dementia. For example, examining the role of inflammation, hormonal changes, and genetic predispositions could provide insights into how these conditions are connected.
The study, “Association between depression and incident dementia: Longitudinal findings from the share study,” was authored by Nicola Veronese, Lee Smith, Ai Koyanagi, Pinar Soysal, Christoph Mueller, Chiara Maria Errera, Giusy Vassallo, Laura Vernuccio, Giuseppina Catanese, Marco Solmi, Ligia J. Dominguez, and Mario Barbagallo.
