The idea that how smart you are might be connected with how healthy you are is not new. Those who studied social sciences have probably seen the published works on the subject dating back to 1980s.
The problem is not so easy to study academically, though. It is hard to separate the influence of various social factors on both intelligence level and health from a pure connection between health and brightness. As a result, many of the existing studies have been inconclusive. Factors such as age, sex, social and economic level, and education of the study cohort may seriously affect the conclusions. However, when these factors are taken into account, or the study groups are designed in a way minimizing their influence, rather interesting findings emerge.
To measure the cleverness, most studies use IQ. With all its disadvantages, IQ testing still remains the most reliable measure of intelligence. This article will briefly outline the results of studies investigating possible effects that different IQ levels might have on the health.
First, it is important to ask how IQ and health could be connected. Social components are relatively obvious: lower IQ might mean lower level of knowledge about healthy living, for instance. Also, the gradual progression of some chronic diseases may affect cognitive functions leading to lower IQ in unhealthy people. A published analysis showed that long-term sick leave and disability pension are often related to low cognitive abilities. Obviously, this effect is secondary and does not confirm the link between the initial IQ before the disease and the risk of developing this particular disease.
Apart from these obvious connections, there are genetic and physiological components. Recent research data suggest (twin studies in particular) that 60% of factors influencing our intelligence level are dictated by our genes.
There are many genes that directly or indirectly can influence our IQ: these are the genes involved in functioning of the brain, efficiency of neurotransmission, production of neuromediators and so on. The proteins produced by these genes work on multiple levels, and not only in neurons. They may, for instance, regulate the blood supply to the brain or other organs, or availability of various nutrients to neurons or other cells. These proteins may work in different cells of our body performing similar functions. If a gene works not particularly well in the brain cells, it is also likely to underperform elsewhere. At least, this is a general scientific assumption. However, the same gene may have different effects in different cell types, and therefore the link is not so obvious and not so easy to investigate.
It is interesting to mention what the published studies do not confirm. The data show no gender differences in correlations between mortality/morbidity and the IQ level. One study published in the British Medical Journal also demonstrated quite clearly that there is no correlations between high IQ in childhood and morbidity/mortality rates later in life. In both cases the social factors such as social class and culture were taken into account.
Links Between IQ and Specific Diseases
One study demonstrated that high IQ in men was correlated with the incidence of coronary heart disease, although when socio-economic variables were taken into account the relation was not very strong.
Another study showed that atherosclerosis and hypertension could be linked to lower IQ. This relationship might, to a certain degree, reflect social phenomena, as those with higher IQ levels tend to be better informed and live healthier life styles.
Studies have also shown that a lower IQ in children can lead to obesity in adulthood.
Many of the diseases mentioned above can be causes of, or lead to, stroke. Therefore, it is not surprising that a low IQ is linked to a higher risk of stroke. The latter conclusion in regards to the stroke risk stands even when socioeconomic variables are rigorously taken into consideration.
Psychiatric disorders have also long been considered to have a very close link with high IQ. Many geniuses were known to have rather strange or unpredictable characters, suffered from mood disorders and depression. Indeed, statistics shows that creative people with higher IQ are more likely to suffer from bipolar disorder and mood swings. Most studies done on this subject were small but all show similar results nonetheless.
One study among the students in Swedish schools found that those with higher grades were more likely to show signs of bipolar disorder. However, the study also demonstrated that students with the lowest grades were twice more likely to show signs of bipolar disorder compared to the average students. Interestingly, a New Zealand study showed similar associations between low IQ and psychiatric disorders.
Another study published in The Archive of General Psychiatry showed that people with higher IQ were less likely to suffer from post-traumatic stress disorder. This study has considered socioeconomic variables, as discussed earlier.
Interestingly, a recent study published this year found a higher risk of developing glioma, a type of brain tumor, among university-educated people. The risk is 19% higher in educated men and 23% higher in women with a university degree. The reasons for such correlation remain speculative.
The findings discussed above highlight that both low and high IQ levels can be associated with certain risks. Lower IQ might be linked with poorer general health, while high IQ level is associated with higher chances of psychiatric disorders. It is important to emphasize, however, that these correlations are not very strong – having a specific IQ level, whether it is low or high, does not automatically load your body with associated health problems of any kind. Further research are needed to see how the health and intelligence are connected on genetic and physiological levels: I’m sure there are lots of surprising discoveries there!
Batty, G. (2006). Does IQ explain socioeconomic inequalities in health? Evidence from a population based cohort study in the west of Scotland BMJ, 332 (7541), 580-584 DOI: 10.1136/bmj.38723.660637.AE
Dennis, M., Francis, D., Cirino, P., Schachar, R., Barnes, M., & Fletcher, J. (2009). Why IQ is not a covariate in cognitive studies of neurodevelopmental disorders Journal of the International Neuropsychological Society, 15 (03) DOI: 10.1017/S1355617709090481
Hauser, R., & Palloni, A. (2011). Adolescent IQ and Survival in the Wisconsin Longitudinal Study The Journals of Gerontology Series B: Psychological Sciences and Social Sciences, 66B (Supplement 1) DOI: 10.1093/geronb/gbr037
Khanolkar, A., Ljung, R., Talbäck, M., Brooke, H., Carlsson, S., Mathiesen, T., & Feychting, M. (2016). Socioeconomic position and the risk of brain tumour: a Swedish national population-based cohort study Journal of Epidemiology and Community Health DOI: 10.1136/jech-2015-207002
Lager, A., Bremberg, S., & Vagero, D. (2009). The association of early IQ and education with mortality: 65 year longitudinal study in Malmo, Sweden BMJ, 339 (dec11 1) DOI: 10.1136/bmj.b5282
Wraw, C., Deary, I., Gale, C., & Der, G. (2015). Intelligence in youth and health at age 50 Intelligence, 53, 23-32 DOI: 10.1016/j.intell.2015.08.001
This guest article originally appeared on the award-winning health and science blog and brain-themed community, BrainBlogger: Is Being Clever Dangerous For Your Health?