Low Exercise Capacity Increases the Risk of Low Cognitive Function in Healthy Young Men Born Preterm: A Population-Based Cohort Study

Abstract

Background: Preterm birth is a risk factor for decreased exercise capacity and impaired cognitive functions in later life. The objective of this study was to disentangle the associations between preterm birth, physical fitness and cognitive performance in young adulthood.

Methods: This population-based cohort study included 218,802 young men born in Sweden 1973-1983. Data on birth characteristics was obtained from the Medical Birth Register and linked to exercise capacity assessed by ergometer cycling and cognitive tests performed at conscription for military service in 1993-2001. Cognitive performance was assessed using stanine (STAndard NINE) scores. The results were adjusted for socioeconomic factors.

Results: Exercise capacity was positively associated with cognitive performance across all gestational ages. The sub-group of men who were born extremely preterm (gestational age <28 weeks) and had low exercise capacity exhibited the lowest odds ratio (OR = 0.26, 95%CI:0.09-0.82) of having a cognitive function above the mean stanine score (2.9) for men born at term with normal birth weight. Men born extremely preterm with a high exercise capacity had similar or even higher ORs for cognitive function (OR = 0.59; 95% CI:0.35-0.99) than men born at term with low Wmax (OR = 0.57; 95% CI:0.55-0.59).

Conclusions: Physical fitness is associated with higher cognitive function at all gestational ages, also in young men born extremely preterm. Targeting early physical exercise may be a possible intervention to enhance cognitive performance and educational achievements in populations at risk, such as childhood and adult survivors of preterm birth.

Fig 1. Formation of the study cohort.

All men who were registered in both the Medical Birth Register (MBR) and the Conscript Register formed the primary cohort. Men who did not perform the exercise or the IQ test were excluded as well as men with missing data in the Population and Housing Census. Finally, subjects with data in the MBR which were judged as misclassified were excluded.

Fig 2. Associations of Odds Ratio (OR) for higher cognitive function with Gestational Age (GA) and maximal exercise capacity (W_max).

Men exhibiting a low exercise capacity had lower ORs for cognitive function (blue line) compared to men with average to high W_max (red line). *p<0.05.