As much as 20 percent of people experience their highest-ever rate of psychological distress in middle age, new research spanning multiple decades of post-war British life has found.

In the new study, researchers analysed the mental health of three distinct cohorts, studying data collected in longitudinal studies of participants born in 1946, 1958, and 1970.

The results – a snapshot of the psychological health of Britons from the Baby Boomers to Generation X – suggest mental health disorders peak in middle age, reframing the notion of the midlife crisis, which is under-recognised, researchers say.

"Mental health in adolescence and older age tends to gain much more attention than psychological distress in middle age, despite adults being particularly vulnerable to mental ill-health at this stage of life," explains public health researcher Dawid Gondek from University College London (UCL).

"Our study suggests that increased attention should be paid to the detection and management of mental health in middle age."

In the new research, Gondek and his team analysed data collected from the National Survey of Health & Development (NSHD, studying the health and development of children born in 1946), as well as the National Child Development Study (NCDS, looking at children born in 1958), and the British Cohort Study (BCS70, for children born in 1970).

Looking at a subset of over 28,000 individuals from the three cohorts – including only participants who had experienced some form of psychological distress between age 23 and 69 – the researchers wanted to come up with an age profile of what psychological distress looked like.

For the purposes of the study, psychological distress was defined in general terms, encompassing broad measures of depression and anxiety, but not diagnosing or differentiating between specific mental disorders.

The results showed that the cross-sectional proportion of psychological distress cases was highest in midlife ages in all three cohorts, reaching 19.1 percent at age 53 in NSHD, 15.2 percent at age 50 in NCDS, and 19.9 percent at age 46 in BCS70, following a consistent increase in psychological distress from early adulthood years into middle age.

"Overall, after controlling for cohort differences, the age profile of psychological distress followed an inverted U-shape in adulthood, with symptoms increasing from early- to mid-adulthood, and subsequently declining," the authors explain in their paper, noting that the Generation X cohort, born in 1970, appears to experience the highest consistent rates of mental ill health during adulthood.

"Generation X were more likely to have psychological distress than the Baby Boomers across their lives," says UCL population health researcher George Ploubidis.

"They entered the job market in the late 1980s and early 1990s during a period of recession and high unemployment, and also found it more difficult than earlier generations to get on the housing ladder. As a result, these particular circumstances may have had a lasting effect on the mental health of this generation throughout adulthood."

As for why mental health problems would generally surface more in middle age than in earlier or later life, the researchers aren't entirely sure.

But it's possible, they say, that numerous factors coincide at this particular time in people's lives, putting greater pressures and stresses onto them.

"Midlife tends to involve a 'peak' in career, with middle-aged adults acquiring increasing responsibility as the 'decision-makers' in society, which is accompanied by reduced leisure time," the team writes.

"Midlife individuals were found to experience declining quality and quantity of leisure time, as well as time with friends and family, which may translate into worse mental health."

In addition, middle age is often associated with significant changes to family structure, the researchers say, either in the form of divorce, ongoing parental responsibilities, or having to care for ageing parents.

The researchers acknowledge that there are a number of limitations in their study, which relies upon different measures of psychological distress in the original studies.

Due to this, and the subsequent generality of depression and anxiety symptoms noted in the analysis, the team says the findings don't capture specific mental health problems in the population, such as psychosis or bipolar disorder.

Given all the data come from cohorts living in the UK at specific times in history also means we can't necessarily assume the same trends in psychological distress would appear for people from other places and times.

Nonetheless, the study does seem to reveal a phenomenon in mental health that looks more likely to affect people in middle age than at other times in their life – and it's something we need to know more about, if we're to have a hope of helping people experiencing this midlife surge.

"There is a need for further research to understand processes underlying elevated psychological distress at each life phase (early and mid-20s as well as 40s-50s) and for cross-cohort differences," the authors explain.

"The British birth cohorts, including those following younger participants, are well-suited for studying those mechanisms."

The findings are reported in Psychological Medicine.