Happiness in early adulthood may protect against dementia

Every week I come across studies which show that dementia is not a disease of old age, but rather a condition that has its roots much, much earlier in life—in some instances in the womb. This study confirms many of these earlier studies (reported in TR) but looks at the issue in terms of the connection between early depression and later dementia.

For example, while previous research has shown that poor cardiovascular health can damage blood flow to the brain increasing the risk for dementia, this new study indicates that poor mental health may also take its toll on cognition.

The research adds to a body of evidence that links depression with dementia, but while most studies have pointed to its association in later life, the latest study shows that depression in early adulthood may lead to lower cognition 10 years later and to cognitive decline in old age. The study was published in the Journal of Alzheimer’s Disease.

The researchers used innovative statistical methods to predict average trajectories of depressive symptoms for approximately 15,000 participants aged 20 to 89, divided into three life stages: older, midlife and young adulthood. They then applied these predicted trajectories and found that in a group of approximately 6,000 older participants, 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 in later life.

These results were adjusted for depressive symptoms in other life stages and for differences in age, sex, race, educational attainment, body mass index, history of diabetes and smoking status. For depressive symptoms in midlife, the researchers found an association with cognitive impairment, but this was discounted when they adjusted for depression in other life stages.

What the researchers say: “Several mechanisms explain how depression might increase dementia risk,” said the lead author. “Among them is that hyperactivity of the central stress response system increases production of the stress hormones glucocorticoids, leading to damage of the hippocampus, the part of the brain essential for forming, organizing and storing new memories.”

Other studies have linked depression with atrophy of the hippocampus, and one study has shown faster rates of volume loss in women, she said.

In estimating the depressive symptoms across each life stage, researchers pooled data from younger participants with data from the approximately 6,000 older participants and predicted average trajectories. These participants, whose average age was 72 at the start of the study and lived at home, had been enrolled by the Health Aging and Body Composition Study and the Cardiovascular Health Study. They were followed annually or semi-annually for up to 11 years.

Participants were screened for depression using a tool called the CESD-10, a 10-item questionnaire assessing symptoms in the past week. Moderate or high depressive symptoms were found in 13 percent of young adults, 26 percent of midlife adults and 34 percent of older participants.

Some 1,277 participants were diagnosed with cognitive impairment following neuropsychological testing, evidence of global decline, documented use of a dementia medication or hospitalization with dementia as a primary or secondary diagnosis.

“Generally, we found that the greater the depressive symptoms, the lower the cognition and the faster the rates of decline,” the researchers said. “Older adults estimated to have moderate or high depressive symptoms in early adulthood were found to experience a drop in cognition over 10 years.”

So, what? The rate of depression was increasing rapidly pre-COVID. Much of that increase was among the young—the rate of child depression was increasing alarmingly. This will inevitably lead—as this research points out—to an increase in dementia.

I have said for some time that dementia –and Alzheimer’s in particular—is a disease of modern lifestyle. Multiple studies have failed to find any sign of it in hunter-gatherer societies. There are probably various genetic predispositions to dementia—some have been documented—but these are only predispositions which are triggered by stress, which is also an underlying cause of depression. Most of the increase in stress worldwide is work-related (it increased by 200% in the 10 years prior to the pandemic). Working from home will increase this stress (as a number of studies have shown).

Economic uncertainty—much of it work-related—and poverty are also prime causes of stress-related depression. With increasing inequality these will only continue to cause more mental health problems and therefore more dementia.

In the words of one researcher in this area: “You ain’t seen nothing yet!”

For more on dementia click here. For more on depression click here. For more on work stress click here.