The effect of lead on male fertility : A time to pregnancy (TTP) study

Background Growing attention has been paid in recent decades to the effects on male reproduction of occupational exposures to toxic agents. There is strong evidence that high level exposure to lead, i.e. blood lead level (PbB) > 70 μg/dl, is associated with male infertility and some reports suggest an effect even at lower PbB (i.e. 40 μg/dl). The Cox model was adopted to estimate the Relative Risk of unsuccessful waiting time to pregnancy associated to the exposure to lead. Results A statistically significant difference in fecundability (shorter TTP) in favor of exposed subjects was detected. Nevertheless, longer TTP was associated within the exposed group to higher levels of PbB, even though the gradient is not statistically significant. The exposed workers revealed an average number of children larger than those not exposed, and a clear gradient of the same variable was evident from the lowest to the highest PbB level. Focusing on subjects with one child only, the Cox model confirmed no significant difference in fecundability between exposed and not exposed, whereas a statistically significant longer TTP was associated to the exposure level ≥40 μg/dl. Conclusions It is not easy to assert or to deny the effect of inorganic lead on male fecundity, quantitatively estimated by TTP, with the data available for this study. In fact, while the general data seem to exclude effects of Pb on male fecundability a more detailed analysis suggests an unfavorable effect at relatively high levels of exposure but some confounding attributable to personal and social conditions of the workers cannot be ruled out. Further investigations with a better control of confounding are needed.