People who experience prolonged depressive symptoms starting in young adulthood may have worse thinking and memory skills in middle age, according to a study published in the June 12, 2024, online issue of Neurology®, the medical journal of the American Academy of Neurology. The study also found that depressive symptoms were experienced more often by Black adults than white adults.
Leslie Grasset, PhD, of University of Bordeaux in France, the study’s author, emphasized the importance of this research, stating, “The processes that lead to dementia begin long before signs of the disease become apparent, and previous research has shown that Black adults have a higher risk of dementia than white adults. Our study found that prolonged exposure to elevated depressive symptoms in young adulthood has a negative effect on thinking and memory in middle age, especially for Black adults.”
Study Design and Findings
The study involved 3,117 people with an average age of 30 at the start of the study. Of participants, 47% were Black and 53% were white. Participants were evaluated for depressive symptoms every five years for 20 years, completing questionnaires that assessed changes in appetite or sleep, problems with concentration, and feelings of worthlessness, sadness, or loneliness. Researchers divided participants into four groups based on the progression of their symptoms over time: persistently low symptoms, medium decreasing, persistently medium, or high increasing symptoms. There was a higher proportion of Black participants, 52%, in the persistently medium group, as well as the high increasing depressive symptoms group with 70%.
Five years later, when participants had an average age of 55, they were given three tests to examine thinking and memory skills. After adjusting for factors such as age, physical activity, and total cholesterol, among Black participants, those in the high symptom group had an average score that was 0.64 standard deviations below the average score for the low symptom group. Among white participants, those in the high symptom group had an average score that was 0.40 standard deviations below the average score for the low symptom group.
Implications for Racial Disparities in Dementia Risk
After adjusting for factors such as education, blood pressure, and total cholesterol, researchers found that among Black participants, those in the three groups with high and medium symptoms had worse verbal memory, processing speed, and executive function scores when compared to those in the low group. Among white participants, those in the high symptom group had worse verbal memory and processing speed scores when compared to those in the low symptom group.
“Our results suggest that Black adults are not only more likely to experience worse depressive symptoms trajectories, but these symptoms may lead to worse repercussions on thinking and memory as early as middle age,” said Grasset. “This may help explain some of the disparities in dementia risk at older age.”
Grasset emphasized the importance of addressing racial inequalities when designing interventions to reduce a person’s risk of dementia, stating, “Having more depressive symptoms may be due to inequalities in socioeconomic resources such as housing and income, as well as access to health care and treatment. Racial inequalities should be accounted for when designing interventions to reduce a person’s risk of dementia.”
A limitation of the study was that symptoms were self-reported and no clinical diagnosis of depression was available. It is possible that some participants may not have accurately reported their symptoms.
