Smart people aren't more miserable
Intelligence and physical health
It has long been known that intelligence is associated with lifespan and health. For example, (Cukic et al., 2017) traces the records of 70,000 Scottish citizens in Scotland who were born in 1936 and took the government's intelligence and health screening test at the age of 11 and finds that intelligence measured in childhood and life expectancy have a positive relationship. As can be seen from the graph, there is a linear relationship between the intelligence percentiles and the likelihood of being alive in 2015.
Examining studies on intelligence and life expectancy measured at an early age (Batty et al., 2007), finds that all studies show this relationship.
Similarly, (Deary et al., 2021) reaches the same conclusion in his article examining large-scale studies on intelligence, longevity, and causes of death.
When it comes to specific causes of death, intelligence seems to have a negative relationship with every disease. As intelligence increases, the risk of death due to cancer, respiratory tract, cardiovascular and stomach diseases, stroke, diabetes and Alzheimer's decreases.
Similarly (Fries and Pietschnig, 2022), in their study of 12 European countries, finds a negative relationship between intelligence and environmental factors that increase chronic fitness, symptoms, doctor visits and health risks.
An important aspect of this study is that it shows that the relationship between health and intelligence is not due to environmental reasons. One of the proposed mechanisms for the relationship between intelligence and health was that more intelligent people avoided environmental factors that would increase the risk of illness/death (e.g., smoking and alcohol use, not paying attention to body mass index, etc.), but this large-scale study finds the impact of environmental factors to be minimal. Only there seems to be a statistically significant link between physical activity and intelligence, but its impact is also low.
There are reasons to think that the health-intelligence relationship stems from pleitropy. The systematic review of this relationship (Deary et al., 2019) finds genetic correlations between many health phenotypes and intelligence when examining genetic correlations between different health indicators and intelligence. For example, genetic factors that increase the risk of type 2 diabetes are also negatively associated with intelligence. The following table shows all the relationships. This does not mean that there is a direct pleitropic relation between all of them, but it gives us reason to think that there is a relationship in this direction and to conduct further research.
Similarly, (Hagenaars et al., 2016), in his study of the UK Biobank, finds a genetic correlation between cognitive abilities and many health-related variables, suggesting that this relationship points to a common origin between health and intelligence.
Intelligence and Mental Health
General Psychopathology Factor or p-factor and Intelligence
One of the important developments in the field of psychiatry was studies showing that, similar to the g-factor in intelligence studies, there is a latent p-factor underlying psychopathological/psychiatric disorders. The psychopathology (p) factor is a latent factor that is associated with all psychopathological disorders and increases your risk of having other disorders when you have one disorder. For example, (Allegrini et al., 2020) examines 7,000 pairs of twins for psychopathology and finds a genetic p-factor associated with behavioral and emotional disorders.
But is there a relationship between the p-factor and intelligence?
(Caspi et al., 2014), Weschler finds a negative relationship (-.19) between the Adult Intelligence Scale-IV result and the p factor.
(Harden et al., 2019), in his study of 1900 twins, finds a negative relationship between full-scale IQ, general intelligence, and the p factor (r≈-.20-25)
Specific disorders and intelligence
(Gale et al., 2010) examines the risk of being hospitalized for intelligence and mental impairment as measured in young adulthood. As can be seen from the graph, as intelligence increases, the risk of being hospitalized due to psychological disorders such as schizophrenia, mood disorder, neurosis, personality disorder decrease
(Williams et al., 2022), when he examines the mental state of the highly intelligent people (2 standard deviations or more from the population intelligence average, equivalent to an IQ of 130 and above), he finds that the highly intelligent have lower trauma, anxiety, PTSD, neuroticism and social isolation than the average, in short, they are mentally healthier.
(Hatch et al., 2007) interviews 1800 of those born in the United Kingdom in 1946 and who participated in national cognition and health screening at the age of 8, at age 53, and found that childhood intelligence was negatively associated with depression and anxiety in adult women, but found no such effect for men. But theoretically, because of Lynn's Developmental Theory, we can expect childhood intelligence to have lower predictive power for men when separated by gender.
Based on adult men (Christensen et al., 2018), a study of 620,000 men found that the risk of major depression increased as intelligence declined.
(Tsitsipa and Fontoulakis, 2015) finds that IQ and other cognitive functions are negatively associated with bipolar disorder.
(Kendral et al., 2015), a study of 1.2 million people finds a negative relationship between intelligence and schizophrenia.
Conclusion
In conclusion, it is possible to say that intelligence and both physical and mental health go hand in hand, and that they come from a common origin (i.e., common genetic effects). Smarter people are healthier, live longer, and are more mentally stable.
Bibliography
Allegrini, A. G., Cheesman, R., Rimfeld, K., Selzam, S., Pingault, J., Eley, T. C., & Plomin, R. (2020). The p factor: Genetic analyses support a general dimension of psychopathology in childhood and adolescence. Journal of Child Psychology and Psychiatry,61(1), 30-39. https://doi.org/10.1111/jcpp.13113
Caspi, A., Houts, R. M., Belsky, D. W., Goldman-Mellor, S. J., Harrington, H., Israel, S., Meier, M. H., Ramrakha, S., Shalev, I., Poulton, R., & Moffitt, T. E. (2014). The p Factor: One General Psychopathology Factor in the Structure of Psychiatric Disorders? Clinical Psychological Science,2(2), 119-137. https://doi.org/10.1177/2167702613497473
Christensen, G. T., Rozing, M. P., Mortensen, E. L., Christensen, K., & Osler, M. (2018). Young adult cognitive ability and subsequent major depression in a cohort of 666,804 Danish men. Journal of Affective Disorders,235, 162-167. https://doi.org/10.1016/j.jad.2018.04.035
Čukić, I., Brett, C. E., Calvin, C. M., Batty, G. D., & Deary, I. J. (2017). Childhood IQ and survival to 79: Follow-up of 94% of the Scottish Mental Survey 1947. Intelligence,63, 45-50. https://doi.org/10.1016/j.intell.2017.05.002
Deary, I. J., Hill, W. D., & Gale, C. R. (2021). Intelligence, health and death. Nature Human Behaviour,5(4), 416-430. https://doi.org/10.1038/s41562-021-01078-9
Fries, J., & Pietschnig, J. (2022). An intelligent mind in a healthy body? Predicting health by cognitive ability in a large European sample. Intelligence,93, 101666. https://doi.org/10.1016/j.intell.2022.101666
Gale, C. R., Deary, I. J., Boyle, S. H., Barefoot, J., Mortensen, L. H., & Batty, G. D. (2008). Cognitive Ability in Early Adulthood and Risk of 5 Specific Psychiatric Disorders in Middle Age: The Vietnam Experience Study. Archives of General Psychiatry,65(12), 1410. https://doi.org/10.1001/archpsyc.65.12.1410
Hagenaars, S., Harris, S., Davies, G., Hill, W., Liewald, D., Ritchie, S., Marioni, R., Fawns-Ritchie, C., Cullen, B., Malik, R., Wardlaw, J., Gallacher, J., Pell, J., McIntosh, A., Smith, D., Gale, C., & Deary, I. (2016). Shared genetic aetiology between cognitive functions and physical and mental health in UK Biobank (N = 112 151) and 24 GWAS consortia. Molecular Psychiatry, 9.
Harden, K. P., Engelhardt, L. E., Mann, F. D., Patterson, M. W., Grotzinger, A. D., Savicki, S. L., Thibodeaux, M. L., Freis, S. M., Tackett, J. L., Church, J. A., & Tucker-Drob, E. M. (2020). Genetic Associations Between Executive Functions and a General Factor of Psychopathology. Journal of the American Academy of Child & Adolescent Psychiatry,59(6), 749-758. https://doi.org/10.1016/j.jaac.2019.05.006
Hatch, S. L., Jones, P. B., Kuh, D., Hardy, R., Wadsworth, M. E. J., & Richards, M. (2007). Childhood cognitive ability and adult mental health in the British 1946 birth cohort. Social Science & Medicine,64(11), 2285-2296. https://doi.org/10.1016/j.socscimed.2007.02.027
Kendler, K. S., Ohlsson, H., Sundquist, J., & Sundquist, K. (2015). IQ and Schizophrenia in a Swedish National Sample: Their Causal Relationship and the Interaction of IQ With Genetic Risk. American Journal of Psychiatry,172(3), 259-265. https://doi.org/10.1176/appi.ajp.2014.14040516
Michèle Williams, C., Peyre, H., Labouret, G., Fassaya, J., Guzmán García, A., Gauvrit, N., & Ramus, F. (2022). High Intelligence is not a Risk Factor for Mental Health Disorders[Preprint]. Pathology. https://doi.org/10.1101/2022.05.26.22275621
Tsitsipa, E., & Fountoulakis, K. N. (2015). The neurocognitive functioning in bipolar disorder: A systematic review of data. Annals of General Psychiatry,14(1), 42. https://doi.org/10.1186/s12991-015-0081-z
Intelligence and physical health
It has long been known that intelligence is associated with lifespan and health. For example, (Cukic et al., 2017) traces the records of 70,000 Scottish citizens in Scotland who were born in 1936 and took the government's intelligence and health screening test at the age of 11 and finds that intelligence measured in childhood and life expectancy have a positive relationship. As can be seen from the graph, there is a linear relationship between the intelligence percentiles and the likelihood of being alive in 2015.
Examining studies on intelligence and life expectancy measured at an early age (Batty et al., 2007), finds that all studies show this relationship.
Similarly, (Deary et al., 2021) reaches the same conclusion in his article examining large-scale studies on intelligence, longevity, and causes of death.
When it comes to specific causes of death, intelligence seems to have a negative relationship with every disease. As intelligence increases, the risk of death due to cancer, respiratory tract, cardiovascular and stomach diseases, stroke, diabetes and Alzheimer's decreases.
Similarly (Fries and Pietschnig, 2022), in their study of 12 European countries, finds a negative relationship between intelligence and environmental factors that increase chronic fitness, symptoms, doctor visits and health risks.
An important aspect of this study is that it shows that the relationship between health and intelligence is not due to environmental reasons. One of the proposed mechanisms for the relationship between intelligence and health was that more intelligent people avoided environmental factors that would increase the risk of illness/death (e.g., smoking and alcohol use, not paying attention to body mass index, etc.), but this large-scale study finds the impact of environmental factors to be minimal. Only there seems to be a statistically significant link between physical activity and intelligence, but its impact is also low.
There are reasons to think that the health-intelligence relationship stems from pleitropy. The systematic review of this relationship (Deary et al., 2019) finds genetic correlations between many health phenotypes and intelligence when examining genetic correlations between different health indicators and intelligence. For example, genetic factors that increase the risk of type 2 diabetes are also negatively associated with intelligence. The following table shows all the relationships. This does not mean that there is a direct pleitropic relation between all of them, but it gives us reason to think that there is a relationship in this direction and to conduct further research.
Similarly, (Hagenaars et al., 2016), in his study of the UK Biobank, finds a genetic correlation between cognitive abilities and many health-related variables, suggesting that this relationship points to a common origin between health and intelligence.
Intelligence and Mental Health
General Psychopathology Factor or p-factor and Intelligence
One of the important developments in the field of psychiatry was studies showing that, similar to the g-factor in intelligence studies, there is a latent p-factor underlying psychopathological/psychiatric disorders. The psychopathology (p) factor is a latent factor that is associated with all psychopathological disorders and increases your risk of having other disorders when you have one disorder. For example, (Allegrini et al., 2020) examines 7,000 pairs of twins for psychopathology and finds a genetic p-factor associated with behavioral and emotional disorders.
But is there a relationship between the p-factor and intelligence?
(Caspi et al., 2014), Weschler finds a negative relationship (-.19) between the Adult Intelligence Scale-IV result and the p factor.
(Harden et al., 2019), in his study of 1900 twins, finds a negative relationship between full-scale IQ, general intelligence, and the p factor (r≈-.20-25)
Specific disorders and intelligence
(Gale et al., 2010) examines the risk of being hospitalized for intelligence and mental impairment as measured in young adulthood. As can be seen from the graph, as intelligence increases, the risk of being hospitalized due to psychological disorders such as schizophrenia, mood disorder, neurosis, personality disorder decrease
(Williams et al., 2022), when he examines the mental state of the highly intelligent people (2 standard deviations or more from the population intelligence average, equivalent to an IQ of 130 and above), he finds that the highly intelligent have lower trauma, anxiety, PTSD, neuroticism and social isolation than the average, in short, they are mentally healthier.
(Hatch et al., 2007) interviews 1800 of those born in the United Kingdom in 1946 and who participated in national cognition and health screening at the age of 8, at age 53, and found that childhood intelligence was negatively associated with depression and anxiety in adult women, but found no such effect for men. But theoretically, because of Lynn's Developmental Theory, we can expect childhood intelligence to have lower predictive power for men when separated by gender.
Based on adult men (Christensen et al., 2018), a study of 620,000 men found that the risk of major depression increased as intelligence declined.
(Tsitsipa and Fontoulakis, 2015) finds that IQ and other cognitive functions are negatively associated with bipolar disorder.
(Kendral et al., 2015), a study of 1.2 million people finds a negative relationship between intelligence and schizophrenia.
Conclusion
In conclusion, it is possible to say that intelligence and both physical and mental health go hand in hand, and that they come from a common origin (i.e., common genetic effects). Smarter people are healthier, live longer, and are more mentally stable.
Bibliography
Allegrini, A. G., Cheesman, R., Rimfeld, K., Selzam, S., Pingault, J., Eley, T. C., & Plomin, R. (2020). The p factor: Genetic analyses support a general dimension of psychopathology in childhood and adolescence. Journal of Child Psychology and Psychiatry,61(1), 30-39. https://doi.org/10.1111/jcpp.13113
Caspi, A., Houts, R. M., Belsky, D. W., Goldman-Mellor, S. J., Harrington, H., Israel, S., Meier, M. H., Ramrakha, S., Shalev, I., Poulton, R., & Moffitt, T. E. (2014). The p Factor: One General Psychopathology Factor in the Structure of Psychiatric Disorders? Clinical Psychological Science,2(2), 119-137. https://doi.org/10.1177/2167702613497473
Christensen, G. T., Rozing, M. P., Mortensen, E. L., Christensen, K., & Osler, M. (2018). Young adult cognitive ability and subsequent major depression in a cohort of 666,804 Danish men. Journal of Affective Disorders,235, 162-167. https://doi.org/10.1016/j.jad.2018.04.035
Čukić, I., Brett, C. E., Calvin, C. M., Batty, G. D., & Deary, I. J. (2017). Childhood IQ and survival to 79: Follow-up of 94% of the Scottish Mental Survey 1947. Intelligence,63, 45-50. https://doi.org/10.1016/j.intell.2017.05.002
Deary, I. J., Hill, W. D., & Gale, C. R. (2021). Intelligence, health and death. Nature Human Behaviour,5(4), 416-430. https://doi.org/10.1038/s41562-021-01078-9
Fries, J., & Pietschnig, J. (2022). An intelligent mind in a healthy body? Predicting health by cognitive ability in a large European sample. Intelligence,93, 101666. https://doi.org/10.1016/j.intell.2022.101666
Gale, C. R., Deary, I. J., Boyle, S. H., Barefoot, J., Mortensen, L. H., & Batty, G. D. (2008). Cognitive Ability in Early Adulthood and Risk of 5 Specific Psychiatric Disorders in Middle Age: The Vietnam Experience Study. Archives of General Psychiatry,65(12), 1410. https://doi.org/10.1001/archpsyc.65.12.1410
Hagenaars, S., Harris, S., Davies, G., Hill, W., Liewald, D., Ritchie, S., Marioni, R., Fawns-Ritchie, C., Cullen, B., Malik, R., Wardlaw, J., Gallacher, J., Pell, J., McIntosh, A., Smith, D., Gale, C., & Deary, I. (2016). Shared genetic aetiology between cognitive functions and physical and mental health in UK Biobank (N = 112 151) and 24 GWAS consortia. Molecular Psychiatry, 9.
Harden, K. P., Engelhardt, L. E., Mann, F. D., Patterson, M. W., Grotzinger, A. D., Savicki, S. L., Thibodeaux, M. L., Freis, S. M., Tackett, J. L., Church, J. A., & Tucker-Drob, E. M. (2020). Genetic Associations Between Executive Functions and a General Factor of Psychopathology. Journal of the American Academy of Child & Adolescent Psychiatry,59(6), 749-758. https://doi.org/10.1016/j.jaac.2019.05.006
Hatch, S. L., Jones, P. B., Kuh, D., Hardy, R., Wadsworth, M. E. J., & Richards, M. (2007). Childhood cognitive ability and adult mental health in the British 1946 birth cohort. Social Science & Medicine,64(11), 2285-2296. https://doi.org/10.1016/j.socscimed.2007.02.027
Kendler, K. S., Ohlsson, H., Sundquist, J., & Sundquist, K. (2015). IQ and Schizophrenia in a Swedish National Sample: Their Causal Relationship and the Interaction of IQ With Genetic Risk. American Journal of Psychiatry,172(3), 259-265. https://doi.org/10.1176/appi.ajp.2014.14040516
Michèle Williams, C., Peyre, H., Labouret, G., Fassaya, J., Guzmán García, A., Gauvrit, N., & Ramus, F. (2022). High Intelligence is not a Risk Factor for Mental Health Disorders[Preprint]. Pathology. https://doi.org/10.1101/2022.05.26.22275621
Tsitsipa, E., & Fountoulakis, K. N. (2015). The neurocognitive functioning in bipolar disorder: A systematic review of data. Annals of General Psychiatry,14(1), 42. https://doi.org/10.1186/s12991-015-0081-z
