A recent longitudinal study provides new insight into the association between intelligence in adolescence and mental health outcomes in middle age.
The research indicates that higher intelligence in youth is linked to a lower risk of some common mental health issues at age 50, but a greater likelihood of receiving a depression diagnosis.
Key facts:
- Participants took an IQ test in youth and reported on mental health around age 50.
- Higher IQ was tied to lower depression symptoms and better mental health status at 50.
- However, higher IQ was also associated with an increased chance of a lifetime depression diagnosis.
- Childhood socioeconomic status did not explain much of these relationships.
- Adult socioeconomic status seemed to account for many links between youth IQ and mental health.
Source: Intelligence
Youth IQ Scores & Adult Mental Health (Study)
The study utilized data from the National Longitudinal Survey of Youth 1979 (NLSY79), which tracked a group of nearly 13,000 Americans starting when they were ages 14-22 in 1979.
Participants took the Armed Forces Qualification Test (AFQT) as a measure of IQ from 1980-1984.
The same individuals then completed questionnaires on mental health outcomes around 2012, when they were approximately 50 years old.
In total, 5,793 people completed the mental health assessments at age 50 and had IQ test results from youth available.
This longitudinal design with IQ measured in adolescence provides a relatively strong basis to assess how early intelligence may influence later mental health.
Evaluating Mental Health Outcomes
Participants completed various mental health measures at age 50, allowing the researchers to relate IQ to several outcomes:
- Lifetime diagnosis of major depressive disorder: Based on a simple yes/no self-report of whether a doctor had ever diagnosed the participant with depression.
- Mental health status: Assessed using the Mental Component Summary score from the 12-item Short Form Health Survey (SF-12), a widely used scale.
- Depressive symptoms: Measured via the Center for Epidemiologic Studies Depression Scale (CES-D), a 7-item screening tool.
- Sleep difficulties: Participants reported how often they experienced trouble sleeping, trouble staying asleep, and other sleep issues.
Higher IQ Linked to Lower Depression and Better Mental Health
Analyses adjusting for participants’ age and sex revealed that higher IQ scores in youth were significantly associated with lower depression scores on the CES-D, fewer sleep difficulties, and better mental health status per the SF-12 at age 50.
For example, every 1 standard deviation (SD) higher IQ was linked to scoring 1.6 points lower on the CES-D depression scale, reporting less frequent sleep problems, and 78% lower odds of having poor mental health per the SF-12.
These relationships indicate that higher cognitive abilities in adolescence may protect against mental health issues like depression and poor well-being in mid-life.
The higher resiliency observed for individuals with superior IQs may allow them to better cope with stressors and avoid negative thought patterns.
Surprising Link: Higher IQ & Lifetime Depression Diagnoses
However, paradoxically, higher IQ was also related to an increased likelihood of having received a diagnosis of major depressive disorder from a doctor by age 50.
Specifically, every 1 SD higher IQ was associated with 11% greater odds of a lifetime depression diagnosis.
This finding was contrary to the hypothesis that higher intelligence is protective across mental health outcomes.
It also conflicts with the other observed links between higher youth IQ and lower depression symptoms and better well-being at 50.
The study authors proposed several potential explanations for the surprising positive relationship between IQ and lifetime depression diagnoses:
- Health literacy: People with higher intelligence tend to have greater health literacy, meaning they are better equipped to recognize potential health problems. Thus, they may be more likely to notice symptoms of depression and seek help from a doctor, resulting in an official diagnoses.
- Insurance incentives: In the U.S. healthcare system, a depression diagnosis can enable access to insurance coverage for therapy and medications. Intelligent individuals may therefore be more inclined to strategically seek a diagnosis, even if symptoms are mild.
However, these hypotheses require further investigation to understand the counterintuitive correlation observed here.
Childhood Socioeconomic Status (SES) Does Not Explain the Links
The researchers also tested whether the observed relationships might simply be explained by differences in childhood socioeconomic status (SES).
For example, children from lower SES backgrounds tend to have lower IQs and are more prone to experiencing mental health issues.
However, adjusting the statistical models for childhood SES had little effect.
This indicates that the links between youth IQ and mental health outcomes do not appear to be an artifact of confounding by childhood socioeconomic environment.
Instead, cognitive abilities in adolescence seem to independently predict better or worse mental health outcomes decades later in adulthood.
Adult Socioeconomic Status (SES) May Mediate Associations
Yet, adjusting for adult SES did substantially impact the results.
Accounting for adult socioeconomic factors – like education, income, and occupational status – appeared to mediate many of the observed associations.
For instance, the relationships between higher youth IQ and lower depression, fewer sleep disturbances, and better mental well-being in adulthood were no longer significant after adjusting for adult SES.
This suggests that the apparent protective effects of superior cognitive abilities on these mental health outcomes may operate indirectly through gains in socioeconomic resources in adulthood.
In contrast, adjusting for adult SES amplified the positive link between youth IQ and lifetime depression diagnosis.
This was unexpected and indicates that higher IQ individuals are more likely to get diagnosed with depression during their life, even when accounting for their socioeconomic status.
No Evidence that Sex Influences the Links
Another question was whether the relationships might differ between males and females – but no evidence for sex differences was found.
The associations between IQ and each of the mental health outcomes were consistent across men and women.
This bolsters confidence that higher intelligence broadly influences mental health trajectories regardless of gender.
Study Limitations: Youth Intelligence & Adult Mental Health
While this study had a longitudinal dataset and a large sample size, the findings should be considered in light of some limitations:
- Mental health measures were based on self-report, which is less reliable than clinical assessments and medical records.
- There was no mental health assessment at the initial baseline, so it is unknown if depression or other issues were already present when IQ was measured in youth.
- The lifetime depression diagnosis measure did not indicate when the first diagnosis occurred, so the temporal sequence is unclear.
- Data on other potential mediating factors, like major life stressors or physical health status, were not available.
Conclusions: Cognitive Abilities Protect Against Depression?
This research provides unique evidence that cognitive abilities in adolescence may confer some lasting protective effects against depression and poor mental health into middle age.
However, it also indicates higher IQ could be linked to an increased likelihood of receiving a depression diagnosis earlier in adulthood.
These complex results have several notable implications:
- Early identification of individuals with lower IQs may help target those at higher risk for future mental health problems.
- Interventions aiming to improve emotional regulation and coping strategies could mitigate this elevated risk.
- It appears reducing exposure to adult socioeconomic risk factors like poverty could interrupt the pathway from lower youth IQ to later depression.
- Enhancing mental health literacy across the population may help address the disparity in diagnoses.
Overall, these findings demonstrate that links between prior cognitive abilities and subsequent mental health are multifaceted.
More work is still needed to unravel the causal pathways underlying risks versus resilience.
Nevertheless, this study highlights opportunities to proactively support the emotional well-being of all individuals, especially those with lower youth IQ.
References
- Study: Intelligence in youth and mental health at age 50
- Authors: Christina Wraw et al. (2016)
