Intelligence in early adulthood and life span up to 65 years later in male elderly twins

Background: previous research has reported that greater intelligence in early life is associated with longer lifespan. Whether this relationship is mediated by genetic factors or environmental factors, some of which could be modified by an individual, is unclear. Objective: we examined the association between intelligence test scores, obtained during the 1940s, and age at death in a group of 492 male twin pairs, members of the National Academy of Sciences - National Research Council Twins Registry of WWII veterans. Design: using self-report information collected in the 1960s, we examined whether modifiable risk factors for mortality, such as use of tobacco and alcohol, cardiovascular disease, and body mass index altered the association between intelligence and longevity. Results: when each member of a twin pair was treated as an independent observation, higher intelligence test scores were associated with longer life span (P = 0.0002). Modifiable risk factors were associated with life span as expected. However, in co-twin control analyses in which one twin served as the control for the other twin, neither intelligence nor any modifiable risk factors showed a significant association with life span. Conclusion: our findings suggest that genetics and early life environmental factors contribute heavily to lifespan and when one controls for these factors using twins, the effect of intelligence on longevity is diminished.