The happiness quotient in early adulthood, according to researchers, may be linked to the prevention of dementia in old age. While studies have shown that poor cardiovascular health can impair blood flow to the brain, increasing the risk of dementia, a new study led by UC San Francisco suggests that poor mental health may also have an impact on cognition.
The study adds to a growing body of evidence linking depression to dementia. However, while most studies have focused on the association in later life, the UCSF study shows that depression in early adulthood may lead to lower cognition 10 years later and cognitive decline in old age. The findings will be published in the Journal of Alzheimer’s Disease.
It turns out that your emotional state in early adulthood influences your cognition ten years later, as well as your cognition in old age. Researchers discovered that those estimated to have elevated depressive symptoms in early adulthood had a 73% higher risk of cognitive impairment, while those estimated to have elevated depressive symptoms later in life had a 43% higher risk. According to experts, it could be due to an increase in stress hormones caused by depression, which could damage the brain’s hippocampus, which is in charge of forming, organizing, and storing new memories.
While research has shown that poor cardiovascular health can damage blood flow to the brain increasing the risk for dementia, a new study indicates that poor mental health may also take its toll on cognition.
The researchers used novel statistical methods to forecast average trajectories of depressive symptoms for approximately 15,000 participants ranging in age from 20 to 89, divided into three life stages: older, midlife, and early adulthood. They then applied these predicted trajectories to a group of approximately 6,000 older participants and discovered that the odds of cognitive impairment were 73 percent higher for those estimated to have elevated depressive symptoms in early adulthood and 43 percent higher for those estimated to have elevated depressive symptoms later in life.
These findings were adjusted for depressive symptoms in other life stages, as well as differences in age, gender, race, educational attainment, BMI, diabetes history, and smoking status. The researchers discovered an association between depressive symptoms in midlife and cognitive impairment, but this was ruled out when they controlled for depression in other life stages.
Excess Stress Hormones May Damage Ability to Make New Memories
“Several mechanisms explain how depression may increase dementia risk,” said first author Willa Brenowitz, Ph.D., MPH, of the University of California, San Francisco’s Department of Psychiatry and Behavioral Sciences, and the Weill Institute for Neurosciences. “One of them is that hyperactivity of the central stress response system increases the production of the stress hormones glucocorticoids, resulting in damage to the hippocampus, the part of the brain essential for forming, organizing, and storing new memories.”
Other studies have linked depression to hippocampus atrophy, and one study found that women lose volume at a faster rate, she said. Researchers pooled data from younger participants with data from approximately 6,000 older participants to predict average trajectories of depressive symptoms across each life stage. The Healthy Aging and Body Composition Study and the Cardiovascular Health Study enrolled these participants, whose average age was 72 at the start of the study and who lived at home. They were monitored on an annual or semi-annual basis for up to 11 years.
U-Shaped Curve Adds Credence to Predicted Trajectories
While assumed values were used, the authors stated that no longitudinal studies across the life course had been completed. “Imputed depressive symptom trajectories fit a U-shaped curve, which is consistent with age-related trends in other research,” they wrote.
The CESD-10, a 10-item questionnaire assessing symptoms in the previous week, was used to screen participants for depression. Moderate to severe depressive symptoms were found in 13% of young adults, 26% of midlife adults, and 34% of older participants.
Following neuropsychological testing, evidence of global decline, documented use of a dementia medication, or hospitalization with dementia as a primary or secondary diagnosis, 1,277 participants were diagnosed with cognitive impairment.
“In general, we found that the more severe the depressive symptoms, the worse cognition and the faster the rates of decline,” said Brenowitz, who is also affiliated with the UCSF Department of Epidemiology and Biostatistics. “Older adults with moderate or high depressive symptoms in early adulthood were found to have a drop in cognition over a 10-year period.”
With up to 20% of the population suffering from depression at some point in their lives, it’s critical to understand its role in cognitive aging, according to senior author Kristine Yaffe, MD, of UCSF’s departments of Psychiatry and Behavioral Sciences and Epidemiology and Biostatistics. “Future research is required to confirm these findings, but in the meantime, we should screen for and treat depression for a variety of reasons.”
