Most of these studies have been conducted
on middle aged adults and it is worthwhile to
remember that lung function in this age group
may be the result of several mechanisms.27 A
reduced lung function in middle age may result
from a low maximally attained lung function
due to either low lung function at birth or
decreased growth of lung function during
childhood and adolescence, a shortened plateau
phase during early adult life, or an
increased decline in lung function in later adult
life. The important unanswered question
remains: which risk factors linked to socioeconomic
status are causally related to the occurrence
of COPD? The link is likely to be multifactorial
and includes prenatal exposures, more
frequent lower respiratory tract illness in childhood,
housing conditions, air pollution, environmental
tobacco smoke, diet, and other lifestyle
factors including smoking, in addition to
possible genetic factors. As these factors may or
may not be directly associated with socioeconomic
status, they will be briefly discussed in
more detail. A list of the factors of interest in
this review is given in table 2.