Cardiovascular fitness is associated with cognition in young adulthood

Abstract

During early adulthood, a phase in which the central nervous system displays considerable plasticity and in which important cognitive traits are shaped, the effects of exercise on cognition remain poorly understood. We performed a cohort study of all Swedish men born in 1950 through 1976 who were enlisted for military service at age 18 (N = 1,221,727). Of these, 268,496 were full-sibling pairs, 3,147 twin pairs, and 1,432 monozygotic twin pairs. Physical fitness and intelligence performance data were collected during conscription examinations and linked with other national databases for information on school achievement, socioeconomic status, and sibship. Relationships between cardiovascular fitness and intelligence at age 18 were evaluated by linear models in the total cohort and in subgroups of full-sibling pairs and twin pairs. Cardiovascular fitness, as measured by ergometer cycling, positively associated with intelligence after adjusting for relevant confounders (regression coefficient b = 0.172; 95% CI, 0.168-0.176). Similar results were obtained within monozygotic twin pairs. In contrast, muscle strength was not associated with cognitive performance. Cross-twin cross-trait analyses showed that the associations were primarily explained by individual specific, non-shared environmental influences (> or = 80%), whereas heritability explained < 15% of covariation. Cardiovascular fitness changes between age 15 and 18 y predicted cognitive performance at 18 y. Cox proportional-hazards models showed that cardiovascular fitness at age 18 y predicted educational achievements later in life. These data substantiate that physical exercise could be an important instrument for public health initiatives to optimize educational achievements, cognitive performance, as well as disease prevention at the society level.

Fig. 1.

Study design. The conscription register data were linked with the National Swedish Board of Education school records database to obtain grades from the final year of compulsory school (age 15 y), the Multi-Generation Register for data on full brothers, the Swedish Twin Register for information on zygosity, and Statistics Sweden National Longitudinal Integration Database for Health Insurance and Labour Market Studies (LISA) for information on education and occupation.

Fig. 2.

Mean levels of intelligence stanine scores by cardiovascular fitness or muscular strength at age 18 y. For each cognitive measure, all means significantly differed from the others, with the exception of cardiovascular fitness scores 6 vs. 7 and 8 vs. 9 in F. In B, the means of global intelligence score for muscular strength scores 4–9 were not significantly separated from each other. The SDs were 1.8–2.0 (A), 1.8–2.3 (B), and 0.8–1.3 (C–F). The P value was <0.0001 for all associations. For regression and correlation coefficients, see Table 1.

Fig. 3.

Change in cardiovascular fitness between age 15 y and 18 y predicts intelligence scores. (A) Schematic presentation of the model. Note that the regression line is not perfectly straight in reality, but it has essentially this appearance in the various analyses. (B) From all subjects with physical education grades at age 15 y and cardiovascular fitness scores at age 18 y, the 10% of subjects with the highest and lowest changes in fitness scores compared with predicted scores were selected (<10th percentile; 10% lowest vs. predicted scores; >90th percentile, 10% highest vs. predicted scores; 10th-90th percentile, remaining 80%). Mean global intelligence, logical, verbal, visuospatial, and technical scores were compared among the 3 percentile groups and significant differences were found among all groups (P < 0.0001). The SDs were 1.81–1.97.