Discussion
This study shows an association between secular
improvements in air quality in southern California
and measurable improvements in lung-function
development in children. Improved lung
function was most strongly associated with
lower levels of particulate pollution (PM2.5 and
PM10) and nitrogen dioxide. These associations
were observed in boys and girls, Hispanic white
and non-Hispanic white children, and children
with asthma and children without asthma, which
suggests that all children have the potential to
benefit from improvements in air quality.
In addition to improvements in lung-function
development from 11 to 15 years of age, we also
found a strong association between a reduction
in air pollution and a reduction in the proportion
of children with clinically low FEV1
and FVC
at 15 years of age. In general, the age range of
11 to 15 years captures a period during which
lungs are developing rapidly in both boys and girls.
Lung-function development continues in girls until
their late teens and in boys until their early 20s,
but at a much-reduced rate as compared with the
rate during the earlier adolescent period.15,16 It is
therefore likely that the improved function we
observed in the children who were less exposed
to the pollutants will persist into their adulthood.
A higher level of lung function in early adulthood
may decrease the risk of respiratory conditions.17
However, the greatest benefit of improvements
in lung-function development may occur later in
life, because it has been shown that greater lung
function in adulthood can contribute to lower
risks of premature death and other adverse health
outcomes.18-24 Consistent with the growth effects
we have observed in children, there is evidence