"生育危机"真的只是危言耸听吗?

Are today's young men less fertile than their fathers were? It's a controversy in the fertility field, with some experts raising the alarm over what some are calling a 'sperm crisis' because they believe men's sperm counts have been decreasing for a decade or more.

当今青年男性的生育能力是不是弱于他们父辈年轻的时候？这是生育学领域中的一个争议话题。部分专家就一些人所说的“精子危机”发出了警告，因为他们相信，十多年来男性精子数一直在下降。

Experts here for the European Society of Human Reproduction and Embryology annual conference last week debated the issue for an entire day.

前不久，在欧洲人类生殖与胚胎学会(European Society of Human Reproduction and Embryology)的伦敦年会上，专家们围绕这个问题辩论了一整天。

One recent analysis found that in France, the sperm concentration of men decreased by nearly one-third between 1989 and 2005. Most but not all studies from several European nations with large databases and the ability to track health records have found that over the past 15 years or so, the counts of healthy men ages 18 to 25 have significantly decreased. This comes after a prominent study from the 1990s suggested that sperm count has decreased by half over the last half-century.

最近的一项分析发现，从1989年到2005年，法国男性精子密度下降接近三分之一。在多个拥有大型数据库、能够跟踪健康记录的欧洲国家，几乎所有研究都已经发现，在过去15年左右，18到25岁健康男性的精子数明显降低。上世纪90年代的一项著名研究也表明，之前半个世纪男性的精子数下降了一半。

Many experts questioned the validity of those findings. There are huge variations in results by country and region. Certain areas, especially in the developing world, haven't been studied at all. In the U.S., some historical data suggest a decrease in sperm count among American men, but no published recent data exist.

很多专家对这些结论的有效性提出质疑。不同国家和地区的结果千差万别，某些地区，特别是发展中国家根本就没有对此的研究。美国有一些历史数据表明该国男性精子数减少，但并没有近期数据发表。

Understanding if men are producing less sperm has implications beyond male fertility and couples who want children. The same environmental factors that might harm reproduction may also impact other parts of the body. Sperm count has even been linked with life expectancy, independent of cause of death.

弄清楚男性精子数有没有减少，其意义不仅仅止于男性生育能力问题和想要小孩的夫妻。可能有损生育能力的环境因素同样也有可能影响人体的其他部分。精子数甚至还被发现与预期寿命相关，不管死因是什么。

'It's a public health indicator,' says Joelle Le Moal, an epidemiologist at the French Institute for Public Health Surveillance near Paris.

巴黎附近的法国公共卫生监测研究所(French Institute for Public Health Surveillance)的流行病学家若埃勒・莫阿尔(Joelle Le Moal)说：“它是一个公共卫生指标。”。

Proponents say that exposure to pesticides, endocrine-disrupting chemicals like Bisphenol A and lifestyle habits like sitting for too long contribute to the proposed sperm crisis. And there is increasing evidence that sperm count, like other health conditions, may be influenced by what happens to people early in life, even in the womb.

支持者说，暴露于杀虫剂、双酚A等内分泌干扰物以及久坐不动之类的生活方式，都是所谓精子危机的造成因素。而且越来越多的证据表明，精子数和其他健康状况一样，也有可能受到生命早期、甚至是在子宫内所发生情况的影响。

'If our gametes, male or female, are not produced in the right manner, it could impact the next generation's health,' says Dr. Le Moal.

莫阿尔说：“如果我们配子（不管是精子还是卵子）的产生方式有问题，下一代的健康就有可能受到影响。”

In general, men produce upward of 60 million sperm per milliliter of semen. As long as the count is roughly greater than 40 million per ml, men are considered fertile and have the same chance of getting their partners pregnant as someone who produces a higher count.

总体上讲，男性一毫升精液的精子数在6,000万以上。只要每毫升精子数大致超过4,000万，男性就被认为具有生育能力。即使和某个精子数更高的人相比，其让伴侣受孕的概率也是一样的。

But below that threshold and particularly under about 20 million per ml, their ability to help conceive drops. It may take a couple longer than a year to conceive -- a problem known as subfertility -- or they may not succeed at all.

但如果低于这个门槛、特别是低于每毫升约2,000万的密度，那么他们让伴侣怀孕的能力就下降了。一对夫妻可能要花一年以上的时间才能怀上孩子──这被称为“弱育”(subfertility)问题──他们甚至还有可能根本就怀不上。

Not everyone in the field agrees a sperm crisis exists. Critics say that sperm concentration in a population is incredibly difficult to measure for a number of reasons, including the primary one of how to find men representative of the population. Tracking men who show up at a fertility clinic, for instance, would skew the results one way. Neither do sperm donors accurately stand for all the men in a region. Some recent studies have examined young men applying for military service, though the participation rate in the research tends to be low.

并不是生育学领域内所有人都认为有精子危机存在。批评者说，人群中的精子密度非常难以测量，原因有很多，首先便是如何找到人群中具有代表性的男性。比方说，如果是跟踪那些前往不孕不育医院就诊的男性，那么跟踪结果就有可能一边倒。捐精者也不能准确代表一个地区内的全部男性。近期曾有一些研究考察了申请参军的年轻男性，但这种研究的参与率往往不高。

In addition, there could be errors in measurement because of any number of immediate environmental factors, including the length of abstinence, scrotal temperature and time of year.

除此以外，由于禁欲时间、阴囊温度和季节等一个或多个直接的环境因素，也可能引起测量误差。

Stefan Schlatt, director of the Center for Reproductive Medicine and Andrology at the University of Munster in Germany, says he doesn't believe there is a sperm crisis world-wide. Even if sperm count decreased over time, it's unclear how many more men fall into the category of subfertile or infertile, Dr. Schlatt says.

德国明斯特大学(University of Munster)生殖医学与男科学中心(Center for Reproductive Medicine and Andrology)主任斯特凡・舒拉特(Stefan Schlatt)认为，并不存在一场世界范围的精子危机。舒拉特说，即使精子数确实是随着时间的推移而下降了，却也不会知道弱育或不育范畴的男性数量增加了多少。

But coordinated studies across Northern Europe found that as many as 1 in 5 young men have sperm counts low enough to affect fertility, according to Richard Sharpe, a male reproductive health specialist at the University of Edinburgh.

但据爱丁堡大学(University of Edinburgh)男性生育健康专家理查德・夏普(Richard Sharpe)说，在北欧展开的联合调查发现，精子数低到影响生育的男性比例已高达五分之一。

The key may be Sertoli cells, which support the testes' germ cells during their 10-week development into becoming sperm. Each Sertoli cell can only support a certain number of germ cells that produce sperm, so the number of Sertoli cells essentially caps a man's maximum production of sperm.

关键之处可能在于支持细胞（Sertoli cell，又译塞托利细胞），这种细胞在睾丸内精子细胞发育成精子的10周过程中为它们提供支持。每一个支持细胞只能支持一定数量的精子细胞，所以支持细胞数量在事实上设定了男性精子产量的上限。

Sertoli cells appear to proliferate in the six months before and after a male child's birth. While outside factors can decrease sperm production, there don't appear to be any that can increase the production above the limit set by the number of Sertoli cells, Dr. Sharpe says.

支持细胞似乎是在男孩出生的前后六个月内增殖。夏普说，外部因素可以降低精子产量，但似乎没有任何外部因素可以将产量提高到支持细胞数量设定的上限之上。

In Dr. Le Moal's study, which she presented last week, she and her colleagues examined data collected by a professional organization in charge of artificial reproductive technique statistics in France, known as Fivnat. The sample consisted of over 26,000 male partners of women who were known to be infertile and going through infertility treatments at clinics around the country from 1989 to 2005. The men weren't known to be infertile, and therefore were considered a more representative sample than studies that focused on men who were seeking treatment for infertility.

莫阿尔在伦敦年会上提交了一份研究报告。在这项研究中，她和同事考察了法国一家名叫“Fivnat”，负责人工生殖技术统计的专业机构收集的数据。样品由2.6万名男性组成；他们的女性伴侣已知不育，并从1989年到2005年在全国各地的医院接受了不孕不育治疗。这些男性是否不育是未知的，因此其代表性被认为优于那些侧重于寻求不孕不育治疗的男性的研究。

The men's semen quality was tested two times in separate laboratories and measured for sperm number, vitality and shape. The researchers averaged the two samples to get a more reliable figure to take into account age and season. In addition, the method of measurement, especially for the sperm's number and vitality didn't change substantially across France during this period, which is a common criticism of such long-term studies, Dr. Le Moal says.

这些男性的精液质量在不同的实验室做了两次检测，测量了精子的数量、活力和形状。研究人员取了两组样本的平均数，以得到一个更可靠的数字，从而把年龄和季节因素考虑进去。莫阿尔还说，这段时期内法国各地的检测方法、特别是测量精子数量和活力的检测方法并没有很大的变化。检测方法的改变是对这类长期研究的常见批评。

They found that during the 17-year study period, men's sperm concentration decreased by nearly a third, or 1.9% a year. In 1989, the average level of sperm for a 35-year-old man was 73.6 million per ml, well above the subfertile threshold, while in 2005 it had dropped to 49.4 million per ml. The results were published in December in the journal Human Reproduction.

他们发现，在这17年的研究期内，男性精子密度下降接近三分之一，即一年下降1.9%。1989年，35岁男性的平均精子密度为每毫升7,360万，远高于弱育的门槛；2005年则已下降到每毫升4,940万。研究结果于2012年12月发表在《人类生殖》(Human Reproduction)杂志上。

Accumulating evidence suggests that early life influences make a difference. Some researchers say that there is a vulnerable period, perhaps between eight and 14 weeks of gestation, in which influences are irreversible. One of the most robust links with decreased sperm count is maternal smoking during pregnancy.

越来越多的证据表明，生命早期的影响会带来不同。一些研究人员说，在生命脆弱期，可能是妊娠八周到14周之间，其受到的影响是不可逆的。与精子数下降相关性最大的因素之一，就是母亲孕期吸烟。

In a study known as Raine of nearly 2,000 males enrolled as babies and now in their early 20s, the size of the testicles was related to total sperm count, and sperm count was more likely to be lower in boys who were born small for gestational age, who were overweight or underweight in childhood or whose mothers smoked during pregnancy.

一项名为“Raine”的研究调查了将近2,000名男性，他们参与调查的时候是婴儿期，现在已经20岁出头。在这项研究中，睾丸的大小与精子总量有关，而在胎龄不足、童年时期过重或过轻、或母亲孕期吸烟的男孩身上，精子数更低的概率更大。

The male's own current marijuana use was also linked to lower sperm count, according to data presented at the conference by Roger Hart, a professor of reproductive medicine at the University of Western Australia.

根据西澳大学(University of Western Australia)生殖医学教授罗杰・哈特(Roger Hart)在年会上提交的数据，男性自己当期吸食大麻也被发现跟精子数更低有关。

Some factors that impact sperm may be reversible. Others have found that how much belly fat men have, even those not overweight, is linked with testosterone levels in young men.

有些影响精子的因素可能是不可逆的。另外一些研究发现，年轻男性腹部脂肪的多少与其睾丸激素水平有关，即便是不超重的男性也是如此。

'By adopting a healthy, balanced diet and lifestyle in pregnancy, you can give your developing baby the very best start in life which will minimize the risk of future diseases,' Edinburgh's Dr. Sharpe says. 'If it's a boy, then this will also make sure that his sperm count, and thus his fertility, is not compromised in any way.' Subscribe to WSJ:

爱丁堡大学的夏普说：“通过在孕期采用健康、均衡的饮食和生活方式，你可以给发育中的婴儿最好的人生开端，从而将未来罹患疾病的风险最小化。”他说：“如果生的是男孩，那么这样做还会确保他的精子数，进而保证他的生育能力无论如何都不会遭到削弱。”