Parental mental illness is linked to lower cognitive scores in young men

Young men who grew up with a parent diagnosed with a mental disorder tend to score slightly lower on cognitive tests in late adolescence. But this link vanishes for children who experienced multiple other hardships, lived with a single parent, or were placed in foster care. The findings were published in the European Journal of Pediatrics.

Mental health conditions are common and can represent a major source of stress in a young child’s environment. The first six years of life are a time of rapid brain development. During this period, children rely heavily on their parents for care and stability. Disruptions in the home can sometimes affect how a child’s cognitive abilities develop over time.

Often, a parent’s mental illness does not happen in isolation. It frequently co-occurs with other stressful situations, such as poverty, physical illness in the family, or parents separating. Scientists refer to the tendency of childhood hardships to cluster together within families as a compounding burden.

Some researchers propose a theory of cumulative disadvantage. This idea suggests that early hardships pile up over time, resulting in worse outcomes for the child’s development. But few studies have looked at how other family hardships might change the specific relationship between a parent’s mental health and a child’s later intelligence.

Tanja Gram Petersen, a researcher at the University of Southern Denmark, led a team to investigate these specific patterns. The researchers wanted to see if having a parent with a mental illness before age six was linked to cognitive performance at age 18. They also wanted to know if this association changed when a child faced other types of adversity during those same early years.

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To find answers, the researchers conducted a large study using data from the Danish nationwide registry system. In Denmark, all residents receive a unique personal identification number. This allows scientists to link individual health records, family relationships, and education data securely and anonymously.

The team identified 125,791 male adolescents born in Denmark between 1996 and 2001. They focused on young men because all 18-year-old male citizens in Denmark are required by law to undergo a military conscription examination. As part of this evaluation, the young men take a standardized cognitive test.

The military test assesses logical, verbal, numerical, and spatial reasoning skills. The researchers standardized the resulting scores to a scale with an average of 100. This made the scores resemble a typical intelligence quotient scale, making it easier to compare the results with other studies.

Using the national registers, the team looked for records of parental mental disorders. They specifically checked if a mother or father had received an inpatient or outpatient psychiatric diagnosis at a hospital before the child’s sixth birthday. About 5.3 percent of the boys in the study had a parent who met this criteria.

The researchers also tracked other hardships the children might have faced before age six. They grouped these events into three categories. The first category involved family health issues, such as the death of a parent or sibling, or a family member with a severe physical illness.

The second category captured socioeconomic disadvantages. This included prolonged family poverty or a parent experiencing long-term unemployment. The third category covered family instability, which included parents living apart, the family moving across municipality lines frequently, or the child being placed in out-of-home care.

Overall, the study found a modest link between parental mental illness and lower offspring test scores. Young men whose parents were diagnosed with a mental disorder scored, on average, 0.91 points lower on the cognitive test at age 18. This was compared to peers whose parents did not have a recorded psychiatric diagnosis.

But when the researchers divided the data based on other hardships, the patterns shifted. For teenagers who lived with both parents up to age six, a parent’s mental illness was linked to a 1.6-point drop in test scores. For boys who lived with only one parent, there was no association between the affected parent’s diagnosis and the child’s test scores.

The results were even more different for children who had been placed in out-of-home care before age six. In that group, having a parent with a mental illness was actually associated with a 3.2-point increase in cognitive scores at age 18. The researchers note that children in the foster system often face severe situations, and these estimates were based on a smaller number of boys, meaning the numbers should be read with caution.

The total number of hardships also mattered. The team counted how many additional stressful events each child experienced. For boys who faced up to two other hardships, a parent’s mental illness was still linked to lower cognitive scores.

But for young men who experienced three or more additional early hardships, the association vanished. These boys already had lower cognitive scores overall, regardless of their parent’s mental health. Having a parent with a psychiatric diagnosis did not reduce their test scores any further.

The researchers note that these results do not prove that a parent’s diagnosis directly causes a drop in intelligence. Both psychiatric conditions and cognitive abilities are heavily influenced by genetics. Families share genes, and they also share home environments. The overlap of inherited traits and stressful surroundings makes it hard to separate exactly what is driving the lower test scores.

If a child already faces multiple hardships, those events might share the same underlying genetic or environmental roots as the parent’s mental illness. Because of this, adding a parental diagnosis to an already stressful environment might not result in any additional measurable impact on the child’s brain development.

The study included a few limitations that readers should keep in mind. The research focused entirely on males, and it is possible that young women might respond differently to childhood adversity. The data also lacked details on the quality of parenting or the presence of abuse and neglect in the home.

Additionally, Denmark provides a robust universal welfare system. Citizens have free access to most health and social services. The ways in which early hardships affect long-term development might look different in countries with less supportive social safety nets.

The researchers believe that reducing early childhood hardships could still yield broad benefits for society. Cognitive ability is linked to many important life outcomes, including physical health, socioeconomic status, and overall mortality. Understanding how different family situations shape cognitive development will help scientists better support children facing multiple hurdles.

The study, “Cognitive ability following exposure to parental mental disorders and other childhood adversities: a population-based cohort study of Danish males in late adolescence,” was authored by Tanja Gram Petersen, Gunhild Tidemann Okholm, Kirstine Davidsen, Rikke Wesselhoeft, Merete Osler, Trine Munk-Olsen, and Mette Bliddal.