Physical fitness during childhood may offer protection against lung problems later in life, a new analysis shows.
Further, there appears to be a dose–response relationship between the degree of fitness improvement during childhood into adolescence and lung capacity in adulthood, Robert J. Hancox, MD, from the Department of Preventive and Social Medicine, Dunedin School of Medicine, University of Otago, New Zealand, and Finn Rasmussen, MD, from the Department of Allergy and Respiratory Medicine, Near East University Hospital, Nicosia, Cyprus, report in an article published February 1 in the European Respiratory Journal.
To evaluate the relationship between fitness and lung function from childhood to early adulthood, the investigators analyzed the findings of two population-based childhood health and development studies. In the prospective, multidisciplinary Odense schoolchild study, researchers followed 1369 children from third grade through age 29 years, conducting spirometry at regular intervals and maximal exercise tests at ages 9, 15, 21, and 29 years. In the Dunedin Multidisciplinary Health and Development Study, researchers followed a birth cohort comprising 1037 children who underwent spirometry testing at the same intervals as the Odense cohort and aerobic fitness tests at ages 15, 26, 32 and 38 years.
The measures of interest for the study included maximal exercise capacity, forced expiratory volume in 1 second (FEV1), forced vital capacity (FVC), and FEV1/FVC ratio.
The results of the Odense study showed that aerobic fitness increased with age into early adulthood but declined after age 21 years, and that FEV1 also peaked in early adulthood, whereas FVC continued to increase up to age 29 years. Similar patterns were observed in the Dunedin study; however, the fitness decline was seen after 26 years, and FVC increased up to age 32 years, the authors report.
Using linear regression, the investigators analyzed associations between maximal aerobic fitness and lung function at each age, adjusting the analyses for sex, height, weight, current asthma, and current smoking (age 15 years and older).
In both studies, aerobic fitness was associated with higher values of FEV1 and FVC at all ages. Improvements in fitness during childhood and adolescence, determined via linear regression analyses comparing V′O2max between each age and FEV1, FVC, or FEV1/FVC at the older age, were associated with increases in lung volumes up to early adulthood.
The researchers note that percentage predicted values for FEV1 and FVC were 2% to 3% higher for each standard deviation improvement in fitness in early adulthood. Specifically, the lung function differences were up to 0.5 L for men and 0.36 L for women in FVC at the age 29 years, and 0.35 and 0.21 L, respectively, at the age of 38 years.
Acknowledging that the strength of the associations between fitness improvements and lung function are modest, the researchers stress that they are not trivial. “Early adulthood is the time of peak lung function, and differences of this magnitude may be clinically important for some individuals. In addition, longitudinal improvements in fitness from childhood to early adulthood were associated with better adult lung function, particularly for males,” they write. “These findings may have public health relevance, particularly in view of concerns about declining levels of physical activity and fitness among young people.”
The associations between fitness and lung volumes weakened with age after early adulthood and were not significant in the older age groups, the authors note. Further, the fact that fitness was not associated with FEV1/FVC ratios indicates that aerobic fitness “is primarily associated with lung size rather than airway calibre,” they write. “These findings suggest that improving physical fitness during childhood and adolescence may enhance peak lung function in early adulthood.”
They note, however, that the direction of the fitness/lung function association is unclear, and reversing the dependent and independent variables in the analyses resulted in similar findings.
“Further research is needed to identify plausible mechanisms by which fitness and lung function may be related. In addition, we need to know whether maintaining fitness will help to preserve lung function in old age. Greater lung volumes and fitness are both associated with lower all-cause mortality,” the authors write.
In an accompanying editorial, Luis Puente-Maestu, MD, from Servicio de Neumología del Hospital Universitario Gregorio Marañón, Madrid, Spain, and William W. Stringer, MD, from the University of California, Los Angeles, Medical Center, and the Geffen School of Medicine at the University of California, Los Angeles, offer some possible explanations for the association. One possibility is that the forceful inspiration and expiration that occurs during exercise strengthens respiratory muscles, they suggest. In addition, “[m]aximum lung inflation and deflation is an important physiological stimulus for the release of surfactant, and finally, among the pneumocyte type II population, there appears to be some stem cells with the potential to develop new alveoli, at least in rodents, after the development period.”
Regardless of the mechanism, the study authors say the “findings of this study give further reason to encourage exercise and the development of fitness in young people.”
Dr. Puente-Maestu and Dr. Stringer agree. “In adults, cardiorespiratory fitness has been shown to be protective against the development of cardiovascular diseases, arterial hypertension, hyperlipidaemia and type 2 diabetes. While these metabolic and cardiovascular benefits of physical activity are of the utmost importance, we tend to neglect that fitness improves lung health too and to complete the picture, the evidence presented in this paper shows that improving fitness in childhood and adolescence results in better lung function in early adulthood,” they write.
Eur Respir J. 2018;51:1701374. Article abstract, Editorial full text
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