UK and US researchers found that more intelligent people are often healthier, and suggest that this could be due to what they describe as a genetic "fitness factor" whereby both body fitness (health) and brain fitness (intelligence) are influenced by genetic differences among people.
The study was the work of scientists at the Institute of Psychiatry, King's College London, the University of Delaware, in Newark, US, and University of New Mexico, in Albuquerque, US. The paper is to be published in the journal Intelligence where an early corrected proof issue was put online on 28 April.
Other studies that have found intelligence and health often go together have suggested it could be due to several things, including childhood poverty, which harms both intelligence and health, and the fact that brighter people may find it easier to learn how to keep healthy by eating the right foods, not smoking and taking regular exercise.
But as lead and corresponding author Dr Rosalind Arden told the press:
"We had a different idea, that there may be an over-arching genetic 'fitness-factor' that influences both intelligence and health, regardless of childhood experiences or healthy lifestyles."
For the study, Arden and colleagues looked at a range of health data from 3,654 middle-aged (age 31-49) male US service veterans who had served around the era of the Vietnam war. Half of the men had served in Vietnam and the other half had served in Germany, the US, and Korea.
The men had had physical exams that gave a range of clinical data on things like ear inflammation, nose malformation, hernia, muscle atrophy (wasting away), club toes, scoliosis (crooked spine), and urine content of glucose, ketones and proteins.
The men had also completed 5 different kinds of cognitive tests and filled in lifestyle questionnaires from which the researchers were able to get data on smoking status, drugs, weight, alcohol consumption, and so on.
The researchers then compiled an index of physical health by aggregating "abnormality counts" in 8 categories and by using a statistical tool called regression analysis they were able to show that intelligence was a signficant positive predictor of 6 of the 8 categories.
This was even after they took into account lifestyle factors such as age, obesity, combat exposure in Vietnam (including to toxins), smoking, alcohol, and drugs.
Arden and colleagues concluded that:
"These results give preliminary support for the notion of a superordinate fitness factor above intelligence and physical health, which could be further investigated with direct genetic assessments of mutation load across individuals."
Arden said that:
"We found that lower intelligence predicted these diverse health problems, and did so more strongly than the life-style factors (smoking, drug use, drinking, obesity, serving in Vietnam)."
"The health problems from head to toe were also mildly inter-correlated with one another, despite having no obvious medical coherence," she added, explaining that:
"These results are consistent with the idea that a genetic 'fitness factor' influences both bodily health and brain function."
Arden explained that while she and her team agreed that factors such as poverty and looking after one's health also make a difference to health, this study, which the authors describe as a "proof of concept", shows there could also be a genetic factor which warrants further investigation.
The researchers defined the genetic "fitness factor" as "an index of general genetic quality that predicts survival and reproductive success
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