近年来，关于精子数量下降的报道层出不穷。一篇由 Levine 等人于 2017 年发表的论文分析了 1973 年至 2011 年间 42935 名男性的 185 项研究，结果显示平均精子数量从该时期初期的 9900 万个精子/毫升下降至今天的 4700 万个精子/毫升。Levine 等人于 2022 年发表的论文扩展了先前的分析，纳入了来自发展中国家的研究，包括了 223 项研究和 57,168 名男性，结果基本一致。

🤔 **精子数量下降的趋势:** 多项研究表明，男性精子数量在过去几十年中呈下降趋势。Levine 等人 2017 年的论文分析了 185 项研究，发现平均精子数量从 1973 年的 9900 万个精子/毫升下降至 2011 年的 4700 万个精子/毫升。2022 年的扩展分析进一步证实了这一趋势。

🤰 **生育能力的影响:** 精子数量下降是否会影响生育能力？研究表明，精子数量下降到一定程度后，确实会影响自然受孕的概率。然而，体外受精（IVF）技术的存在可以弥补精子数量不足的问题。

📈 **未来趋势:** 研究人员使用线性模型预测，如果精子数量下降趋势持续下去，未来 10-20 年内，男性精子数量可能达到影响生育能力的临界点。然而，线性模型可能存在局限性，真实情况可能更加复杂。

🤔 **其他因素的影响:** 除了精子数量下降，其他因素也可能影响生育能力，例如生活方式、环境污染、压力等。因此，需要进一步研究这些因素对生育能力的影响。

👨‍🔬 **研究的局限性:** 尽管研究表明精子数量下降的趋势，但研究结果也存在一定的局限性。例如，研究样本的代表性、数据收集方法、研究设计等因素都可能影响研究结果。需要进一步研究来证实精子数量下降的趋势及其影响。

🤔 **未来展望:** 为了更好地了解精子数量下降的原因及其影响，需要进行更多深入的研究。同时，也需要关注男性健康，采取措施改善生活方式、减少环境污染、减轻压力等，以促进男性生育能力的改善。

https://astralcodexten.substack.com/p/declining-sperm-count-much-more-than  Is Sperm Count Declining?

People say it is.

Levine et al 2017 looks at 185 studies of 42935 men between 1973 and 2011, and concludes that average sperm count declined from 99 million sperm/ml at the beginning of the period to 47 million today.

Levine et al 2022 expands the previous analysis to 223 studies and 57,168 men, including research from the developing world. It finds about the same thing.

Source: Figure 3 here

The “et al” includes Dr. Shanna Swan, a professor of public health who has taken the results public in the ominously-named Count Down: How Our Modern World Is Altering Male and Female Reproductive Development, Threatening Sperm Counts, and Imperiling the Future of the Human Race.

Is Declining Sperm Count Really "Imperiling The Future Of The Human Race”?

Swan’s point is that if sperm counts get too low, presumably it will be hard to have babies (though IVF should still work).

How long do we have?

This graph (source) shows pregnancy rate by sperm count per artificial insemination cycle. It seems to plateau around 30 million.

An average ejaculation is 3 ml, so total sperm count is 3x sperm/ml. Since sperm/ml has gone down from 99 million to 47 million, total count has gone down from ~300 million to ~150 million.

150 million is still much more than 30 million, but sperm count seems to have a wide distribution, so it’s possible that some of the bottom end of the distribution is being pushed over the line where it has fertility implications.

But Willy Chertman has a long analysis of fertility trends here, and concludes that there’s no sign of a biological decline. Either the sperm count distribution isn’t wide enough to push a substantial number of people below the 30 million bar, or something else is wrong with the theory.

Levine et al model the sperm decline as linear. If they’re right, we have about 10 - 20 more years before the median reaches the plateau’s edge where fertility decreases, and about 10 years after that before it reaches zero. Developing countries might have a little longer.

It feels wrong to me to model this linearly, although I can’t explain exactly why besides “it means sperm will reach precisely 0 in thirty years, which is surely false”. The authors don’t seem to be too attached to linearity, saying that “Adding a quadratic or cubic function of year to meta-regression model did not substantially change the association between year and SC or improve the model fit”.

Still, the 2022 meta-analysis found that the trend was, if anything, speeding up with time, so it doesn’t seem to be obviously sublinear.