Swan S H, Elkin E P, Fenster L
Reproductive Epidemiology Section, California Department of Health Services, Emeryville, CA 94608, USA.
Environ Health Perspect. 1997 Nov;105(11):1228-32. doi: 10.1289/ehp.971051228.
In 1992 a worldwide decline in sperm density was reported; this was quickly followed by numerous critiques and editorials. Because of the public health importance of this finding, a detailed reanalysis of data from 61 studies was warranted to resolve these issues. Multiple linear regression models (controlling for abstinence time, age, percent proven fertility, specimen collection method, study goal and location) were used to examine regional differences and the interaction between region (United States, Europe, and non-Western countries) and year. Nonlinear models and residual confounding were also examined in these data. Using a linear model (adjusted R2 = 0. 80), means and slopes differed significantly across regions (p = 0. 02). Mean sperm densities were highest in Europe and lowest in non-Western countries. A decline in sperm density was seen in the United States (studies from 1938-1988; slope = -1.50; 95% confidence interval (CI), -1.90--1.10) and Europe (1971-1990; slope = -3.13; CI, -4.96- -1.30), but not in non-Western countries (1978-1989; slope = 1.56; CI, -1.00-4.12). Results from nonlinear models (quadratic and spline) were similar. Thus, further analysis of these studies supports a significant decline in sperm density in the United States and Europe. Confounding and selection bias are unlikely to account for these results. However, some intraregional differences were as large as mean decline in sperm density between 1938 and 1990, and recent reports from Europe and the United States further support large interarea differences in sperm density. Identifying the cause(s) of these regional and temporal differences, whether environmental or other, is clearly warranted.
1992年有报告称全球精子密度下降；随后很快出现了大量批评意见和社论。鉴于这一发现对公共卫生的重要性，有必要对61项研究的数据进行详细的重新分析以解决这些问题。使用多元线性回归模型（控制禁欲时间、年龄、已证实的生育百分比、样本采集方法、研究目的和地点）来研究区域差异以及区域（美国、欧洲和非西方国家）与年份之间的相互作用。还对这些数据进行了非线性模型和残余混杂因素的分析。使用线性模型（调整后的R2 = 0.80），各区域的均值和斜率存在显著差异（p = 0.02）。欧洲的平均精子密度最高，非西方国家最低。在美国（1938年至1988年的研究；斜率 = -1.50；95%置信区间（CI），-1.90--1.10）和欧洲（1971年至1990年；斜率 = -3.13；CI，-4.96 - -1.30）观察到精子密度下降，但在非西方国家（1978年至1989年；斜率 = 1.56；CI，-1.00 - 4.12）未观察到下降。非线性模型（二次模型和样条模型）的结果相似。因此，对这些研究的进一步分析支持美国和欧洲的精子密度显著下降。混杂因素和选择偏倚不太可能解释这些结果。然而，一些区域内差异与1938年至1990年精子密度的平均下降幅度一样大，并且来自欧洲和美国的近期报告进一步支持了精子密度存在较大的区域间差异。明确这些区域和时间差异的原因，无论是环境因素还是其他因素，显然是有必要的。
