In an aging society, it is crucial to understand why some people live long and others do not. There has been a proliferation of studies in recent years that highlight the importance of psycho-behavioral factors in the ways of aging, one of those psychological components is intelligence. In this meta-analysis, the association between intelligence and life expectancy in late adulthood is analysed through the Hazard Ratio (HR). The objectives are:
- (i) to update a previous meta-analysis, especially the estimate of the association between survival and intelligence;
- (ii) to evaluate the role of some moderators, especially the age of the participants, to explore intelligence–mortality throughout adulthood and old age.
The results show a positive relationship between intelligence and survival (HR•: 0.79; 95% CI: 0.81–0.76). This association is significantly moderated by the years of follow-up, the effect size being smaller the more years elapse between the intelligence assessment and the recording of the outcome.
The authors concluded that intelligence is a protective factor to reach middle-high age, but from then on survival depends less and less on intelligence and more on other factors.
The consistency of the primary studies is remarkable. This suggests that the association is real. Yet, the question remains: what causes the relationship between intelligence and longevity? Factors such as childhood environment, family income, schooling, and healthy/unhealthy lifestyle habits (diet, exercise, tobacco use, alcohol, illnesses), have been studied. There seems to be a reciprocal dynamic association between intelligence and health throughout life, and although there are several constructs associated with health/ illness and death (e.g., parental social class, intelligence in youth, more education, higher health literacy, healthy behaviors, and more affluent social class) shared genetic differences are likely to account for only a small proportion of these associations.
Arden and colleagues analyzed three twin studies (from the U.S., Denmark, and Sweden) and found a small positive phenotypic correlation between intelligence and lifespan, furthermore, in the combined sample, the genetic contribution to covariance was 95%; in the US study, 84%; in the Swedish study, 86%, and in the Danish study, 85%. These authors pointed out that any genetic factors contributing to intelligence and mortality may operate indirectly via good health choices.
Following this line of argument, I might (with my tongue placed firmly in my cheek) postulate that intelligence leads people to opt for medical treatments that are effective and thus prolong life, while avoiding so-called alternative medicines (SCAMs).