An obstructive impairment of ventilatory
function in the NHANES III
population was correlated with urinary
cadmium levels even after adjustment
for pack years and cotinine level—a
point in favour of cadmium being
relevant independently. Although variability
in puff frequency and depth of
inhalation may play a role in the implicit
discordance between reported pack
years and urinary cadmium, the major
factor could be the notorious inaccuracy
with which smokers estimate their
levels of consumption. If all underestimate
by similar degrees, the effect
on epidemiological investigation would
be minor, but the likelihood is that a
minority provide accurate estimates
while the majority provide estimates
with variable degrees of inaccuracy. In
such circumstances, urinary cadmium
may simply provide a more accurate
reflection of cumulative tobacco consumption.