Does Depression Increase the Risk of Cognitive Decline?

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A new study has looked for links between depression and cognitive decline. Bangmaha Art / EyeEm / Getty Images
  • The researchers studied adults with depressive symptoms and projected their risk of developing cognitive impairment later in life.
  • People living with depression in early adulthood had a higher risk of developing dementia.
  • People with more severe depressive symptoms in early and late adulthood had a higher risk of developing severe cognitive decline.

According to the authors of a recent study, up to 20% of people will experience an episode of clinical depression in their lifetime.

Scientists have established that depression coexists with dementia at the end of life and that depression can be an early symptom of the disease.

However, in a study published in the Alzheimer’s Disease Journal, scientists report that depression in young adults is associated with a 59% higher risk of developing dementia.

Medical News Today asked the study’s first author, Dr. Willa Brenowitz, a San Francisco epidemiologist, about the results. She noted:

“We found that higher depressive symptoms in early adulthood and later in life were associated with late-life cognitive impairment in older adults. And that could mean depressive symptoms in early adulthood [are] potential risk factors for dementia and should be investigated further.

Dr Brenowitz, lead researcher Dr Kristine Yaffe and their colleagues pooled data from four large pre-existing groups of participants to make a total of about 15,000 people aged 20 to 89.

All four groups are part of ongoing studies looking at risk factors for cardiovascular disease or reduced body composition and function in the elderly.

Next, the researchers used a complex statistical method called imputation. They wanted to understand whether depression in early adulthood is associated with an increased risk of dementia.

Dr. Brenowitz defined imputation as “[t]trying to make associations that would not be possible otherwise. She explained to MNT:

“Imputation is about assigning a value to missing data. The underlying idea is this: we lack data from these elderly people on their [depressive symptoms as younger adults]. So, we try to place a value on what we think of to be their depressive symptoms. And, to do this, we need data on other [young] people we think are similar: people who are tradeable.

By comparing young people with older people with similar characteristics, scientists could draw more valid conclusions. To make sure the groups were similar, they compared similar traits, called covariates.

Dr Brenowitz explained, “We took people who look alike, based on certain covariates […] – it’s the age that’s different. We also included other covariates, such as smoking and cardiovascular risk factors. We therefore created this model which corresponds to the depression trajectories for all participants in [the] four different studies.

Dr Brenowitz admits that there is uncertainty in this unique model, which involves assumptions. However, these methods help scientists avoid excluding large groups of people that we want to better understand.

Previous work suggests possible mechanisms that make people living with depression more susceptible to dementia.

People with depression have hyperactivity in the area of ​​the brain that stimulates the adrenal glands to produce more glucocorticoids, such as the stress hormone cortisol. Higher cortisol levels can damage the hippocampus, a part of the brain that is important for cognitive function and memory.

Scientists have also identified that people living with Alzheimer’s disease can have hippocampal atrophy. Dr Brenowitz clarified for MNT:

“Those who suffer from depression have reduced hippocampal volumes. It is believed to be due to an increase in stress hormones, [and] because the hippocampus is a region more sensitive to damage to health […], it is also more susceptible to Alzheimer’s disease.

She explained that the hippocampus is a “vulnerable region that could tip over into a non-ideal state, where we end up with a sort of loss of volume. […] which may be independent of Alzheimer’s disease.

Dr Brenowitz continued: “He could already [be] a stroke of depression, then [a person is] more likely to have Alzheimer’s disease or to be more susceptible to it.

Research suggests that other mechanisms that contribute to cognitive decline may also be at work.

Depression can contribute to dementia through vascular disease, increased inflammation, decreased nerve growth factors, or increased accumulation of amyloid, a brain protein strongly associated with the disease. Alzheimer’s.

The researchers caution that their study estimates associations, not causation, between depression in early adulthood and cognitive impairment in late adulthood.

Depression in early adulthood was not the only factor that increased the risk of dementia in these people. People with more severe depressive symptoms in early adulthood and later in life also showed a higher association with more severe cognitive decline.

Dr Brenowitz said:

“At the end of life, it’s hard to tell the chicken and the egg: what happened first? People who develop dementia often have a 20-year decline trajectory, so it’s difficult to determine. Is it early dementia syndrome or is it due to other risk factors for dementia, such as vascular disease? “

Scientists conclude that the onset of adulthood may be a critical time to alter risk factors for dementia, such as depression. Current midlife interventions to reduce the likelihood of developing dementia include improving cardiovascular risk and managing diabetes, which may play a role in cognitive disorders.

Dr Brenowitz acknowledged that the team’s study raises difficult questions. She noted that it remains to be seen whether an aggressive fight against midlife risk factors or depressive symptoms in early adulthood will affect rates of cognitive impairment in later life.

“I feel like there is a window in early adulthood where people start to move past the feeling that they have nothing to do, and they start to think that they should have a life. life [healthier lifestyle]. They start to develop good habits that will impact not only cognitive impairment, but also physical and mental health later on. “

– Dr Willa Brenowitz

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Hector Hedgepeth

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