Abstract
BackgroundIncreasing numbers of survivors of preterm birth are growing into adulthood today. Long-term health-effects of prematurity are still poorly understood, but include increased risk for diabetes, obesity and cardiovascular diseases in adult life. To test if reduced physical fitness may be a link in the causal chain of preterm birth and diseases in later life, the association of preterm birth and adult exercise capacity was investigated. The hypothesis was that preterm birth contributes independently of other risk factors to lower physical fitness in adulthood.Methods and FindingsPopulation-based national cohort study of all males conscripting for military service in 1993–2001 and born in Sweden 1973–1983, n = 218,820. Data were retrieved from the Swedish Conscript Register, the Medical Birth Register and the Population and Housing Census 1990. Primary outcome was the results from maximal exercise test (Wmax in Watt) performed at conscription. Association to perinatal and socioeconomic risk factors, other co-variates and confounders were analysed. General linear modelling showed that preterm birth predicted low Wmax in a dose-response related pattern, with 25 Watt reduction in Wmax for the lowest gestational ages, those born ≤27 weeks. Low birth weight for gestational age also independently predicted low Wmax compared to normal and high birth weight (32 Watt reduction for those with a birth weight Standard Deviation Score <2). Low parental education was significantly associated with reduced Wmax (range 17 Watt), as well as both low and high current BMI, with severe obesity resulting in a 16 Watt deficit compared to Wmax top performance.ConclusionBeing born preterm as well as being born small for gestational age predicts low exercise capacity in otherwise healthy young men. The effect size of being born preterm equal or exceed that of other known risk factors for unfitness in adults, such as low parental education and overweight.
Highlights
Advances in perinatal medicine have dramatically increased survival after preterm birth [1,2]. This progress is very welcome for women delivering preterm and their families, there is an increasing concern that preterm birth may be an emerging risk factor for chronic lung problems [3,4,5], arterial hypertension [6,7,8] and type 2 diabetes [9,10,11], which predicts accelerated aging, cardiovascular disease and early death [12]
Most studies report Physical Activity (PA) as health promoting independently of other factors [13], but the effect may be mediated through changes in insulin sensitivity [15], physical fitness and body weight [15,18]
Several previous studies have used birth weight as a proxy for Gestational age (GA) or included subjects according to birth weight [3,5,19,23], resulting in a selection bias towards growth restricted infants
Summary
Advances in perinatal medicine have dramatically increased survival after preterm birth [1,2] This progress is very welcome for women delivering preterm and their families, there is an increasing concern that preterm birth may be an emerging risk factor for chronic lung problems [3,4,5], arterial hypertension [6,7,8] and type 2 diabetes [9,10,11], which predicts accelerated aging, cardiovascular disease and early death [12]. Observational studies indicate that subjects born very or extremely preterm end up less physically active or less resilient to PA in later life [5,19,20,21,22], contemporary and large population-based follow-up studies on PA and exercise capacity in all adult survivors of preterm birth are lacking. Long-term health-effects of prematurity are still poorly understood, but include increased risk for diabetes, obesity and cardiovascular diseases in adult life. The hypothesis was that preterm birth contributes independently of other risk factors to lower physical fitness in adulthood
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