New research from the United Kingdom has found that people who experience recurrent episodes of depression throughout adulthood are more at risk of developing memory problems later in life.

Scientists have already shown that depression and other mental health problems can affect a person's memory in the short term. For instance, a study that the journal Cognition and Emotion published in 2016 found that individuals with dysphoria—a persistent sense of unhappiness or dissatisfaction that is often a symptom of depression—had poorer working memory than people without any mental health problems.

Now, however, researchers from the University of Sussex in Brighton, United Kingdom, have found evidence that links experiencing mental health problems throughout adulthood to memory problems at the age of 50 years.

The implications, says study author Darya Gaysina, are that "the more episodes of depression people experience in their adulthood, the higher risk of cognitive impairment they have later in life. This finding highlights the importance of effective management of depression to prevent the development of recurrent mental health problems with long-term negative outcomes."

In the new longitudinal study, the findings of which appear in the British Journal of Psychiatry, researchers analyzed the data of 9,385 people born in the United Kingdom in 1958, which the National Child Development Study (NCDS) has been collecting. This new study is the first to look at the long-term relationship between mental and cognitive health.

Mental health problems and memory

To date, the NCDS has followed this cohort for more than 60 years, collecting information about each participant's health at the ages of 7, 11, 16, 23, 33, 42, 44, 46, 50, and 55 years. Additionally, these participants reported their affective symptoms at the ages of 23, 33, 42, and 50 years and agreed to take memory and other cognitive function tests when they reached 50 years of age.

Gaysina and colleagues looked at how often the participants experienced mental health symptoms throughout the study period and assessed their performance in terms of memory function at age 50. The researchers used a word-recall test to assess the participants' memory, and they also evaluated each person's verbal memory, verbal fluency, information-processing speed, and information-processing accuracy.

The investigators report their findings in the study paper, writing that the "accumulation of affective symptoms across three decades of adulthood (from age 23 to age 50) was associated with poorer cognitive function in midlife," and, specifically, with poorer memory.

Although experiencing a single episode of depression or another mood disorder did not seem to affect a person's memory in midlife, the researchers explain that going through depression and anxiety repeatedly throughout adulthood was a good predictor of poorer cognitive function at age 50.

"We knew from previous research that depressive symptoms experienced in mid-adulthood to late-adulthood can predict a decline in brain function in later life, but we were surprised to see just how clearly persistent depressive symptoms across three decades of adulthood are an important predictor of poorer memory function in midlife," says the study's first author Amber John.

Calling for an 'investment in mental health'

In the study paper, the researchers emphasize that the main strength of the current research lies in its numbers, noting that it involved "a large, nationally representative sample with a long follow-up period."

At the same time, they caution that the data did have its limitations, the main one being that the participants undertook cognitive function assessments only once, at age 50. As a result, the investigators were unable to trace potential changes in cognitive function over time.

Moreover, they explain that at the point when the participants undertook the tests assessing their memory and other cognitive functions, these exams were limited and checked for fewer factors than more recent assessments.

However, the University of Sussex research team also believes that the current findings should be a wake-up call, particularly for governmental policy-makers and health-care providers, but also for individuals who may have a tendency to put mental health self-care on the back burner.

"With the publication of this research, we're calling for the government to invest in mental health provision to help stem the risk of repeated episodes of depression and anxiety," says John.

"From an individual's perspective," she adds, "this research should be a wake-up call to do what you can to protect your mental health, such as maintaining strong relationships with friends and family, taking up physical exercise, or practicing mindfulness meditation—all of which have been shown to boost mental health."

Finally, she advises "seeing your [doctor] for advice if you feel you need help with depression or anxiety" rather than allowing the problem to develop.