Zheng Y, Bonde J P, Ernst E, Mortensen J T, Egense J
Steno Institute of Public Health (Departments of Occupational Medicine and Neurobiology), University of Aarhus, Denmark.
Int J Epidemiol. 1997 Dec;26(6):1289-97. doi: 10.1093/ije/26.6.1289.
There is circumstantial evidence that human sperm count may have declined during past decades. The purpose of this study was to identify the association between semen quality and year of birth.
The study comprised 8608 men consulting four Danish medical centres from 1968 to 1992 because of infertility. Data on semen quality and urogenital disorders were obtained from medical records while lifestyle data were collected from a subset of the population by a postal questionnaire (response 80%). Semen characteristics were analysed as a linear function of year of birth, centre, season and calendar year at time of semen examination, sexual abstinence and lifestyle factors. Effects of age were accounted for by restriction and stratified analysis.
The sperm count declined with increasing year of birth at two of the four centres, but this association disappeared when confounders were adjusted for. Within the subset of men born 1950-1970 we revealed a decrease in the average sperm count by 1.9 mill/ml (95% confidence interval [CI]: 1.45, 2.27) per one advancing year of birth. This finding was consistent across centres even after adjustment for effects of covariates. The proportion of morphologically normal sperm cells changed in parallel with the sperm count, while semen volume did not decline in any time periods.
We found a birth cohort effect on sperm count and morphology among Danish infertile men born after 1950 but not in men born in the first part of the century. The findings are compatible with an environmental impact during prenatal life but the evidence is far from unequivocal.
有间接证据表明，过去几十年间人类精子数量可能有所下降。本研究旨在确定精液质量与出生年份之间的关联。
该研究纳入了1968年至1992年间因不育问题前往丹麦四个医疗中心就诊的8608名男性。精液质量和泌尿生殖系统疾病的数据来自病历，而生活方式数据则通过邮寄问卷从部分人群中收集（回复率80%）。精液特征被分析为出生年份、中心、精液检查时的季节和日历年、禁欲时间和生活方式因素的线性函数。通过限制和分层分析来考虑年龄的影响。
在四个中心中的两个中心，精子数量随出生年份的增加而下降，但在对混杂因素进行调整后，这种关联消失了。在1950年至1970年出生的男性子集中，我们发现出生年份每增加一岁，平均精子数量就会减少1.9百万/毫升（95%置信区间[CI]：1.45，2.27）。即使在对协变量的影响进行调整后，这一发现仍在各中心保持一致。形态正常的精子细胞比例与精子数量平行变化，而精液体积在任何时间段均未下降。
我们发现，1950年后出生的丹麦不育男性的出生队列对精子数量和形态有影响，但本世纪上半叶出生的男性则没有。这些发现与产前生活中的环境影响相符，但证据远非确凿无疑。
