R, Z Chen, L Pothier, L Ryan and L Altshul. 2003. The relationship
between human semen parameters and environmental exposure to polychlorinated
biphenyls and p,p’-DDE. Environmental
Health Perspectives, on line 19 May 2003.
et al. demonstrate a significant dose-response relationship
between PCB 138 and sperm count, mobility and morphology. Higher
exposures were associated with poorer semen quality. They also found
suggestions of associations with other PCB congeners and with the
sum of PCB congeners, but not as strong. Limited evidence of association
between DDE levels and sperm motility emerged from their analysis.
did they do? Hauser et al. determined sperm count,
motility and % normal sperm in a sample of men who had come with
their partner to a fertility lab at Massachusetts General Hospital
for treatment of infertility. At the time of enrollment, it was
not known whether the couple's infertility was due to male or female
et al. took blood the same day they obtained sperm samples,
and analyzed the serum for p,p'-DDE and 57 different PCB
examine the relationship between the contaminants and sperm parameters,
they first determined which men had sperm characteristics indicating
fertility problems. They used criteria
established by the World Health Organization, based on sperm count,
sperm motility and sperm morphology.
then studied whether the likelihood that a man would have sperm
characteristics beneath these reference criteria was related to
the concentration of contaminants in his serum. They limited these
analyses to 3 PCB congeners (118, 138, and 153), p,p'-DDE, and sums
of PCB congeners.
do this for a given chemical, they divided the sample of men into
based on their measured contamination, and then calculated the odds
of subfertile sperm for each tertile. The odds ratios were corrected
for abstinance time, age and smoking status.
did they find? In the 212 participants, 46% had sperm measurements
above the reference criteria for all three measurements. The remainder
all had one or more sperm measurements beneath reference criteria:
19% with sperm count beneath 20 million per ml; 46% with less than
50% motile sperm; and 27% with less than 4% of sperm shaped normally.
of their sample (79%) was composed of Caucasian men. They averaged
36 yrs of age. Most (73%) had never smoked.
PCB congener, PCB 138, showed a strong dose-response relationship
with sperm motility and sperm morphology and a lesser (non-significant)
trend for sperm count. Men with higher levels of PCB 138 were
more likely to have sperm parameters beneath reference values.
calculated using men with all sperm values above reference
level as base. Adapted from Hauser et al. 2003, Table
of the other individual PCB congeners (118 and 153) were associated
with changes in odds-ratios. There was weak evidence for an association
with DDE, with higher in the middle and highest quartiles.
a multivariate analysis using sperm count as a continous variable
(actual measurement) instead of as a dichotomous variable (above
or below the reference value), Hauser et al. found a strong
inverse relationship between PCB 138 and sperm count: the more PCB
138, the lower the sperm count(p < 0.008).This multivariate regression
included age, abstinence time and smoking history as potential confounders.
et al. also combined the PCB measurements into groups based
on their mode of action: estrogen-like PCBs, dioxin-like PCBs, and
cytochrome C P450 enzyme-inducing PCBS. For this analysis, they
summed the concentrations of congeners within each group and then
determined, as above, whether the odds-ratios of different tertiles
indicated an association with sperm parameters.
this analysis, only enzyme-inducing PCBs revealed a dose-response
pattern. Odds ratios for both poor motility and deformed morphology
rose with PCB tertile. These trends were significant before adjustment
for confounding variables, but not afterward, although the trends
remained visible in the data after adjustment.
does it mean? These results add weight to prior findings
indicating that PCB levels may affect sperm parameters adversely,
at levels experienced by many people. The nature of the current
study design, however, prevents any conclusions about causality.
research draws attention in particular the importance of analyzing
different congeners separately, or in biochemically coherent subgroups,
as it appears from these results that effects on sperm vary from
congener to congener.
effort by Hauser et al. to examine together congeners that
share modes of action ("dioxin-like," estrogenic, enzyme
inducing) is an important advance. Refinements in this approach
may allow detection of trends that in this first effort are not
to the authors, this research is continuing, and additional publications
will follow with larger samples and more sophisticated analysis.