Apostoli P, Bellini A, Porru S, Bisanti L
Institute of Occupational Health, University of Brescia (I), P.le Spedali Civili, 1-25125 Brescia, Italy.
Am J Ind Med. 2000 Sep;38(3):310-5. doi: 10.1002/1097-0274(200009)38:3<310::aid-ajim10>3.0.co;2-9.
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 microg/dl, is associated with male infertility and some reports suggest an effect even at lower PbB (i. e. < 50 microg/dl). The aim of this study is to shed more light on the postulated association between occupational exposure to relatively low levels of inorganic lead and reduced fertility in men estimated by the length of time taken to conceive: time to pregnancy (TTP).
A survival analysis of TTP of the last pregnancy was performed adopting the Kaplan Meier methodology. The target population included 782 lead-exposed workers and 165 controls. 251 lead workers and 119 controls were finally eligible and interviewed. Lead-exposed subjects were distributed into four exposure levels according to their blood lead concentration (i.e. < 20; 20-29; 30-39, and >/= 40 microg/dl). The Cox model was adopted to estimate the Relative Risk of unsuccessful waiting time to pregnancy associated to the exposure to lead.
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 microg/dl.
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.
近几十年来，职业接触有毒物质对男性生殖的影响受到了越来越多的关注。有充分证据表明，高铅暴露水平，即血铅水平（PbB）>70微克/分升，与男性不育有关，一些报告表明，即使在较低的血铅水平（即<50微克/分升）下也有影响。本研究的目的是进一步阐明职业接触相对低水平无机铅与男性生育力降低之间的假定关联，男性生育力通过受孕所需时间来估计：怀孕时间（TTP）。
采用Kaplan Meier方法对最后一次怀孕的TTP进行生存分析。目标人群包括782名铅暴露工人和165名对照。最终有251名铅作业工人和119名对照符合条件并接受了访谈。根据血铅浓度将铅暴露受试者分为四个暴露水平（即<20；20 - 29；30 - 39，以及≥40微克/分升）。采用Cox模型估计与铅暴露相关的怀孕等待时间未成功的相对风险。
检测到生育力方面存在统计学显著差异（较短的TTP），有利于暴露受试者。然而，在暴露组中，较高的血铅水平与较长的TTP相关，尽管这种梯度在统计学上不显著。暴露工人的平均子女数量多于未暴露工人，并且从最低血铅水平到最高血铅水平，该变量存在明显梯度。仅关注只有一个孩子的受试者，Cox模型证实暴露组和未暴露组在生育力方面无显著差异，而暴露水平≥40微克/分升与统计学上显著更长的TTP相关。
根据本研究可得的数据，很难断言或否认无机铅对男性生育力（通过TTP定量估计）的影响。事实上，虽然总体数据似乎排除了铅对男性生育力的影响，但更详细的分析表明，在相对高的暴露水平下存在不利影响，但不能排除一些归因于工人个人和社会状况的混杂因素。需要进行更好地控制混杂因素的进一步调查。
