Bahadur G, Ling K L, Katz M
UCLMS, Department of Obstetrics and Gynaecology, London, UK.
Hum Reprod. 1996 Dec;11(12):2635-9. doi: 10.1093/oxfordjournals.humrep.a019184.
Declining sperm count reports have caused enormous concern to both the scientific community and to society. We reproduced the linear regression analysis and the quadratic model analysis using the 50 year sperm count data published in Carlsen's report and found that neither model adequately described the data. The reported decline in sperm count could be due to observational bias and overinterpretation of linear regression. In fact only 36% of the total variability in sperm count was explained by the linear model and 42% by the quadratic model. The linear model was no longer valid when three new European reports on sperm counts were included in the analysis. The quadratic model, however, suggested an upward trend of sperm count after 1975 (R2 = 0.48, P < 0.0001). Factors other than the 'passage of time' may have contributed to the initial decline of sperm count. An immediate candidate was demography. Our analysis showed that sperm counts in USA were significantly higher in 1938-1956 compared with those in 1957-1974 and 1975-1988, but not in the European or Asian/African/South American countries. The variability of the USA sperm count (1938-1988) explained by the linear and quadratic models was found to be 71 and 70% respectively. The quadratic model importantly indicated that the sperm count in USA decreases asymptotically towards a limiting value and global sperm counts could be increasing since 1970. The non-uniform nature of the global sperm count change suggested that local variations in pollution, diet but not global warming were important determinants of reproductive health.
精子数量下降的报告引起了科学界和社会的极大关注。我们使用卡尔森报告中公布的50年精子数量数据进行了线性回归分析和二次模型分析，发现这两种模型都不能充分描述这些数据。报告中精子数量的下降可能是由于观察偏差和对线性回归的过度解读。事实上，线性模型仅解释了精子数量总变异性的36%，二次模型解释了42%。当将三份新的欧洲精子数量报告纳入分析时，线性模型不再有效。然而，二次模型表明1975年后精子数量呈上升趋势（R2 = 0.48，P < 0.0001）。除了“时间推移”之外的其他因素可能导致了精子数量的最初下降。一个直接的候选因素是人口统计学。我们的分析表明，与1957 - 1974年和1975 - 1988年相比，美国1938 - 1956年的精子数量显著更高，但在欧洲或亚洲/非洲/南美洲国家并非如此。线性模型和二次模型对美国精子数量（1938 - 1988年）变异性的解释分别为71%和70%。二次模型重要地表明，美国的精子数量渐近地朝着一个极限值下降，并且自1970年以来全球精子数量可能一直在增加。全球精子数量变化的不均匀性质表明，污染、饮食的局部差异而非全球变暖是生殖健康的重要决定因素。
