Muscular fitness, fatness and inflammatory biomarkers in adolescents

Commentary:
Rona Macniven, Prevention Research Collaboration, University of Sydney

Adolescence is known to be a period of time where physical activity levels decline and weight increases so it is therefore an optimum opportunity for health interventions. This international study looked at the science around inflammatory biomarkers present in blood samples and their relationship with fitness and fatness, finding beneficial health effects of being fit, even in overweight and obese teenagers.

Over 600 young people aged 12.5 to 17.5 years were involved in the study, which was part of the Healthy Lifestyle in Europe by Nutrition in Adolescence (HELENA) research project which took place in 9 European countries including France, Greece, Hungary, Spain and Sweden. The adolescents completed a series of fitness tests such as isometric handgrip strength and standing long jump to measure muscular fitness and a 20 m shuttle run test to measure cardiorespiratory fitness. Blood samples were taken to obtain Z-scores of C-reactive protein, complement factors C3 and C4, leptin and white blood cell counts which were summed to create a cluster of inflammatory biomarkers. A series of statistical models tested the relationships between these fitness measures and the biomarkers, adjusting for sex, age, pubertal stage as well as insulin resistance (HOMA-IR) and skinfolds to measure obesity.

Results revealed high muscular fitness was significantly associated with low levels of both single and grouped inflammatory biomarkers, associations which remained after accounting for cardiorespiratory fitness and insulin resistance. Interestingly, after fatness was also accounted for, the associations did not remain, highlighting how even adolescents who were overweight or obesity had favourable biomarkers if they also had high fitness levels. These associations also displayed a dose-response pattern whereby the higher the fitness levels, the more favourable the biomarker profiles.

These findings emulate evidence in adults which shows healthier outcomes among people who are physically active and fit, regardless of whether they are overweight or obese, when compared to people who are inactive and/or unfit but who are within a healthy weight range. Both physical activity and having a healthy body weight are important for populations ultimately and strategies which focus on increasing physical activity in both adults and children, regardless of weight status will be of particular benefit.