Background and aims Physical exercise has been demonstrated to give positive cognitive effects. We have previously reported lower exercise capacity in otherwise healthy young men with low birth weight or preterm birth. The objective of this study was to investigate the association between perinatal risk factors, cognitive performance and physical fitness in young adulthood.

Methods This was a population-based cohort study including 218,915 young men born in Sweden 1973–1981, conscripted for military service in 1993–2001. Data on birth characteristics was obtained from the Medical Birth Register and linked to information on cognitive test scores and results on ergometer cycling test from the Military Conscript Register.

Results Exercise capacity, as measured by ergometer cycling, was positively associated with cognitive performance, as measured by global intelligence stanine scores, p<0.001. The sub-group with shortest gestational age, less than 28 weeks, exhibited both the lowest cognitive test scores and the lowest exercise capacity. Low birth weight standard deviation scores (BWSDS) for gestational age was associated with lower cognitive performance in a stepwise manner. Using ordinal regression analysis, low BWSDS remained independently associated with low cognitive scores in young adult age.

Conclusions The lower cognitive performance observed in young adults born prematurely or with low birth weight is associated with physical fitness. Targeting physical exercise may be an intervention to enhance cognitive performance and educational achievements in a population at risk, such as survivors of preterm birth and poor fetal growth.