新研究惹争议!男性精子数量持续下降,可能导致人类灭绝
2017/07/28
一项最新发表的研究称,西方国家的男性精子浓度和总精子数量正在显著下降。同时领导该研究的科学家认为,如果男性精子数量继续以目前的速度下降,人类可能会灭绝。


图片来源:BBC

日前,据BBC报道,根据最新发表在Human Reproduction Update上的一项研究,一名医生警告称,如果男性精子数量继续以目前的速度下降,人类可能会灭绝。

尽管一些专家对这一结论持怀疑态度,但领导该研究的Hagai Levine博士称,他对未来可能发生的事情“非常担心”。

在这篇题为“Temporal trends in sperm count: a systematic review and meta-regression analysis”的论文中,研究人员评估了近200项研究的结果后发现,北美、欧洲、澳大利亚和新西兰男性精子的数量在不到40年内似乎减少了一半。


图片来源:Human Reproduction Update

规模最大

这是有史以来规模最大的一次评估:汇集了1973 -2011年185项研究的结果。这也是首个关于精子数量的系统回顾和荟萃分析。

具体来说,研究发现,来自北美、欧洲、澳大利亚和新西兰的男性精子浓度下降了52.4%,总精子数量下降了59.3%。研究还表明,这种下降速度还在持续,甚至可能还会增加。

相比之下,南美、亚洲和非洲男性精子的数量没有被观察到出现显著的下降。不过,研究人员指出,调查这些地区男性精子的研究非常少。

Levine博士向BBC表示,如果这一趋势持续下去,人类将会灭绝。对于Levine博士的这一说法,未参与该研究的科学家们认为,得出这样的结论可能还为时过早。


Hagai Levine博士(图片来源:Hebrew University)

存有争议

许多先前的研究曾表明,发达国家男性精子数量出现了类似的大幅下降,但持怀疑态度的人认为,这些研究大部分是有缺陷的。一些研究仅调查了相对较少数量的男性,或者只调查了出现在生育诊所的男性。还有一些担心称,那些声称精子数量下降的研究(比没有得出这种结论的研究)更有可能被发表在科学期刊上。

另一个问题是,早期计算精子的方法可能高估了其真实的数量。这些因素可能会导致精子数量下降的错误观点。

不过,这项新研究涉及了更广的范围,使用了严格的荟萃回归分析。这让一些“怀疑者”对结论的怀疑程度有所下降。英国谢菲尔德大学的Allan Pacey教授便是其中的一员。他说:“Levine博士和他的同事领导的这项研究解决了先前研究的许多缺陷。”

不过,Pacey教授也表示,尽管新研究降低了错误的可能性,但它并没有完全消除这些错误。他说:“研究结果应该被谨慎对待。这场辩论还没有得到解决,显然还有很多工作要做。”


图片来源:Raycat/iStockphoto

敲响警钟

参与该研究的Shanna H Swan教授说:“自从25年前首次被报道以来,精子数量减少一直是人们关注的焦点。我们的研究首次表明,这种下降趋势是强劲的,而且还在持续。”

不过,目前,还没有明确的证据能够解释精子数量大幅下降的这种现象。这可能与接触化学物质、肥胖、吸烟、压力、饮食等有关。

Levine博士认为,鉴于精子数量对男性生育和人类健康的重要性,这项研究为全球的研究人员和卫生部门敲响了警钟。现在迫切的需要找出精子数量下降的原因以及逆转这种趋势的方法。他说:“我们必须采取行动,例如,加强对人造化学物质的监管。此外,我们必须继续努力解决吸烟和肥胖问题。”

参考资料:

Sperm count drop 'could make humans extinct'

Study shows a significant ongoing decline in sperm counts of Western men

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  • Temporal trends in sperm count: a systematic review and meta-regression analysis

    BACKGROUND Reported declines in sperm counts remain controversial today and recent trends are unknown. A definitive meta-analysis is critical given the predictive value of sperm count for fertility, morbidity and mortality. OBJECTIVE AND RATIONALE To provide a systematic review and meta-regression analysis of recent trends in sperm counts as measured by sperm concentration (SC) and total sperm count (TSC), and their modification by fertility and geographic group. SEARCH METHODS PubMed/MEDLINE and EMBASE were searched for English language studies of human SC published in 1981–2013. Following a predefined protocol 7518 abstracts were screened and 2510 full articles reporting primary data on SC were reviewed. A total of 244 estimates of SC and TSC from 185 studies of 42 935 men who provided semen samples in 1973–2011 were extracted for meta-regression analysis, as well as information on years of sample collection and covariates [fertility group (‘Unselected by fertility’ versus ‘Fertile’), geographic group (‘Western’, including North America, Europe Australia and New Zealand versus ‘Other’, including South America, Asia and Africa), age, ejaculation abstinence time, semen collection method, method of measuring SC and semen volume, exclusion criteria and indicators of completeness of covariate data]. The slopes of SC and TSC were estimated as functions of sample collection year using both simple linear regression and weighted meta-regression models and the latter were adjusted for pre-determined covariates and modification by fertility and geographic group. Assumptions were examined using multiple sensitivity analyses and nonlinear models. OUTCOMES SC declined significantly between 1973 and 2011 (slope in unadjusted simple regression models −0.70 million/ml/year; 95% CI: −0.72 to −0.69; P < 0.001; slope in adjusted meta-regression models = −0.64; −1.06 to −0.22; P = 0.003). The slopes in the meta-regression model were modified by fertility (P for interaction = 0.064) and geographic group (P for interaction = 0.027). There was a significant decline in SC between 1973 and 2011 among Unselected Western (−1.38; −2.02 to −0.74; P < 0.001) and among Fertile Western (−0.68; −1.31 to −0.05; P = 0.033), while no significant trends were seen among Unselected Other and Fertile Other. Among Unselected Western studies, the mean SC declined, on average, 1.4% per year with an overall decline of 52.4% between 1973 and 2011. Trends for TSC and SC were similar, with a steep decline among Unselected Western (−5.33 million/year, −7.56 to −3.11; P < 0.001), corresponding to an average decline in mean TSC of 1.6% per year and overall decline of 59.3%. Results changed minimally in multiple sensitivity analyses, and there was no statistical support for the use of a nonlinear model. In a model restricted to data post-1995, the slope both for SC and TSC among Unselected Western was similar to that for the entire period (−2.06 million/ml, −3.38 to −0.74; P = 0.004 and −8.12 million, −13.73 to −2.51, P = 0.006, respectively). WIDER IMPLICATIONS This comprehensive meta-regression analysis reports a significant decline in sperm counts (as measured by SC and TSC) between 1973 and 2011, driven by a 50–60% decline among men unselected by fertility from North America, Europe, Australia and New Zealand. Because of the significant public health implications of these results, research on the causes of this continuing decline is urgently needed.

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