Högskolan i Skövde

Background: Muscular and cardiorespiratory fitness (MF and CRF) have been related to inflammation. Thus, the aim of this study was to assess the relationship between fitness and high-sensitivity C-reactive protein (hs-CRP) in European children both in the cross-sectional and longitudinal analysis. Methods: Three hundred and fifty-seven children (46.2% males) aged 2–9 years with hs-CRP measured, data from MF and CRF, diet quality, objectively measured physical activity (PA) and screen time at baseline and follow-up after 2 years were included. Body mass index z-score (zBMI), waist circumference (WC) and fat mass index (FMI) were assessed. MF and CRF were also dichotomized as follows: low-medium quartiles (Q1–Q3) and highest quartile (Q4). Results: At follow-up, children with the highest CRF (Q4) showed a lower probability of having high hs-CRP. In the longitudinal analysis, children who improved their CRF over time showed a significantly lower probability (p < 0.05) of being in the highest hs-CRP category at follow-up, independently of the body composition index considered: odds ratio (OR) = 0.22 for zBMI, OR = 0.17 for WC, and OR = 0.21 for FMI. Conclusions: Improving CRF during childhood reduces the odds of an inflammatory profile, independently of body composition and lifestyle behaviours. These highlight the importance of enhancing fitness, especially CRF, to avoid an inflammatory state in children. Impact: Improvements in the cardiorespiratory profile during childhood could reverse an unfavourable inflammatory status.There is a longitudinal and inverse association between CRF and inflammation in children.This is the first longitudinal study assessing the relationship between fitness and inflammation during childhood that takes also into account the lifestyle behaviours.Results from the present study suggest a protective role of fitness already in childhood.Efforts to improve fitness in children should be aimed at as inflammation could trigger future cardiovascular disease.