Adverse effect of outdoor air pollution on cardiorespiratory fitness in Chinese children

Little is known about the health impact of air pollution on children's cardiovascular health. A cross-sectional study was conducted and data was analysed in 2048 Chinese schoolchildren (aged 8–10 years) in three districts of Hong Kong to examine the association between exposure to outdoor air pollution and cardiorespiratory fitness. Annual means of ambient PM₁₀, SO2, NO2 and O₃ from 1996 to 2003 were used to estimate individual exposure of the subjects. Cardiorespiratory fitness was measured for maximal oxygen uptake (VO_2max), predicted by the multistage fitness test (MFT). Height and weight were measured and other potential confounders were collected with questionnaires. Analysis of covariance was performed to estimate the impact of air pollution on complete speed in the MFT and predicted VO_2max. The results showed that children in high-pollution district had significantly lower complete speed and predicted VO_2max compared to those in low- and moderate-pollution districts. Complete speed and predicted VO_2max was estimated to reduce 0.327 km h⁻¹ and 1.53 ml kg⁻¹ min⁻¹ per 10 μg m⁻³ increase in PM₁₀ annual mean respectively, with those in girls being greater than in boys. Being physically active could not significantly result in improved cardiorespiratory fitness in polluted districts. The adverse effect seems to be independent of short-term exposure to air pollution. We concluded that long-term exposure to higher outdoor air pollution levels was negatively associated with cardiorespiratory fitness in Chinese schoolchildren, especially for girls. PM₁₀ is the most relevant pollutant of the adverse effect. Elevated cardiorespiratory fitness observed in physically activate children could be negated by increased amount of inhaled pollutants during exercise.