L, JP Bonde, E Ernst, M Spanô, CY Andersen, M Frydenberg and
J Olsen. 2003. Does Smoking During Pregnancy Affect Sons’
Sperm Counts? Epidemiology 14:278–286.
who smoke more than 10 cigarettes a day while pregnant may be cutting
their son's sperm count, once he reaches adulthood, by almost half.
This effect could be an important contributor to regional and temporal
variation in sperm count.
did they do? Storgaard et al. obtained smoking
histories via questionnaires from the mothers of 265 men, a combination
of twins and pairs of singleton brothers. They then analyzed the
relationship between the mother's smoking pattern during pregnancy
and their son's sperm concentration (aged 20-45 yrs). The men were
questioned about confounding variables like current smoking, occupational
history, month of birth, history of cryptorchidism, abstinence time,
etc., and these were controlled for in the analysis. The scientists
also took blood samples, which they analyzed for reproductive hormone
did they find? Compared to sons whose mothers didn't smoke,
sons whose mothers smoked more than 10 cigarettes per day in pregnancy
had, on average, a 48% reduction in sperm concentration, after adjusting
for confounding variables. These men were 4.3 times more likely
to have a sperm concentration beneath the WHO standard
of 20 million per milliliter. Inhibin-B
levels were suppressed and follicle-stimulating
found no effect on sperm volume or morphology, or on levels of testosterone,
does it mean? As in any epidemiological study, these results
fall short of proving a causal relationship between intense smoking
and lower sperm counts. But Storgaard et al. comment that
if the relationship is causal, "the global smoking epidemic
among women would correspond to a substantial decline in sperm concentration
that may contribute to lower fecundity 20 to 30 years later."
may also contribute to geographic differences in sperm count, as
cultures vary in the degree to which women smoke. Storgaard et
al. cite data comparing smoking rates in Finland vs. Denmark:
the former low, the latter high. As would be predicted from this,
Finnish sperm counts are higher than Danish.
also speculate about the mechanisms by which maternal smoking might
impair sperm production in sons. Tobacco smoke is a complex chemical
mixture, which includes not only chemicals created by burning of
the tobacco itself, but also an array of synthetic chemicals, e.g.,
pesticides, that have been used in the process of growing tobacco
and manufacturing cigarettes. Animal studies have shown that fetal
exposure to tobacco smoke can reduce sperm numbers, and identified
at least two components of tobacco smoke, nicotine and polycyclic
aromatic hydrocarbons, which might be interfering with proper development
of the relevant parts of the male reproductive tract.
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