May 25, 2025, 9:39 am | Read time: 4 minutes
The specific causes of various illnesses are not yet fully understood. However, research continues to uncover new potential risk factors through studied correlations. This list could potentially expand to include a low intelligence quotient (IQ) for conditions such as schizophrenia, depression, and some physical findings. A new meta-analysis revealed a surprising connection. FITBOOK author Laura Pomer reports.
Previous research shows that a low IQ tends to be associated with an increased risk of obesity.1 This alone can have a negative impact on overall health. A new study from the University of Vienna has now examined whether a low IQ in childhood, adolescence, or young adulthood is independently linked to a higher risk of physical and mental illnesses later in life.2 And the results indeed suggest this.
Overview
Study on Low IQ as a Risk Factor for Illnesses
The research model was a comprehensive review followed by a meta-analysis. Initially, the researchers conducted “a systematic literature search,” according to a press release, “and identified 49 relevant studies from tens of thousands of documents.”3 These studies used standardized IQ tests and included healthy control groups. Overall, data from 2.9 million test subjects from eight countries were available, making the study the largest on this topic to date. Most samples came from the United Kingdom, followed by the United States, Denmark, Sweden, and Israel, as well as Finland, New Zealand, and Norway.
Details on the Approach
A so-called multilevel multiverse meta-analysis was used. This is a relatively new and particularly comprehensive research method. It allows scientists to summarize the results of many individual studies and systematically examine how different methodological decisions affect the overall outcome. Additionally, the method considers different data levels, such as differences between studies, countries, or age groups.
For the study, IQ in an early life stage, that is, in childhood, adolescence, or young adulthood (before age 21), was crucial. This largely excluded a reverse relationship—meaning that certain diseases lower intellectual performance. IQ is generally quite stable from childhood onward. However, theoretically, it can deteriorate due to extreme life events like traumatic experiences or brain injuries, but it can also improve through intensive support.
The average age at IQ assessment was 14 years, and the follow-up period averaged 34.1 years.
Low IQ Primarily Favors Mental Illnesses
The meta-analysis concludes that a low IQ in early life stages should be considered an independent risk factor for physical and mental illnesses. Young people with an IQ just 15 points lower had about a 22 percent higher risk for various diseases later in life. This pattern existed across different health conditions, the authors write, but was most pronounced in the area of mental health. Specific illnesses included schizophrenia, depression, anxiety disorders, general personality disorders, post-traumatic stress disorder, alcohol and drug addiction, and substance abuse.
Further analyses showed differences between countries, which depended on the quality of medical care. In countries with a higher standard, the impact of IQ on the likelihood of illnesses was less. Education level also proved to be a significant factor. “This suggests that both health policy measures and educational initiatives could help reduce health inequalities,” the press release states.
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Possible Significance of the Study
It should be noted that the data examined came from highly developed countries, most of them from the United Kingdom. Therefore, the observations are not easily transferable. Additionally, the ratio between male and female samples was 10 to 1. Thus, the results can only be generalized to women to a limited extent. Since these were observational studies, numerous potential influencing factors could not be considered in the evaluation.
Nevertheless, the study provides clear evidence of the significance of IQ in early life as a significant risk factor for later physical and mental illnesses. These findings offer the potential for prevention. Targeted interventions such as educational and health promotions in childhood and adolescence might reduce susceptibility to diseases. FITBOOK reached out to the authors to ask what specific measures might be useful here. Could other socioeconomic variables (e.g., employment status, living environment) influence the observed relationship? A response is still pending.