"生育危機"真的只是危言聳聽嗎?
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.
當今青年男性的生育能力是不是弱於他們父輩年輕的時候？這是生育學領域中的一個爭議話題。部分專家就一些人所說的“精子危機”發出了警告，因爲他們相信，十多年來男性精子數一直在下降。
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，在歐洲人類生殖與胚胎學會(European Society of Human Reproduction and Embryology)的倫敦年會上，專家們圍繞這個問題辯論了一整天。
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.
最近的一項分析發現，從1989年到2005年，法國男性精子密度下降接近三分之一。在多個擁有大型數據庫、能夠跟蹤健康記錄的歐洲國家，幾乎所有研究都已經發現，在過去15年左右，18到25歲健康男性的精子數明顯降低。上世紀90年代的一項著名研究也表明，之前半個世紀男性的精子數下降了一半。
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.
很多專家對這些結論的有效性提出質疑。不同國家和地區的結果千差萬別，某些地區，特別是發展中國家根本就沒有對此的研究。美國有一些歷史數據表明該國男性精子數減少，但並沒有近期數據發表。
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.
弄清楚男性精子數有沒有減少，其意義不僅僅止於男性生育能力問題和想要小孩的夫妻。可能有損生育能力的環境因素同樣也有可能影響人體的其他部分。精子數甚至還被發現與預期壽命相關，不管死因是什麼。
'It's a public health indicator,' says Joelle Le Moal, an epidemiologist at the French Institute for Public Health Surveillance near Paris.
巴黎附近的法國公共衛生監測研究所(French Institute for Public Health Surveillance)的流行病學家若埃勒・莫阿爾(Joelle Le Moal)說：“它是一個公共衛生指標。”。
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.
支持者說，暴露於殺蟲劑、雙酚A等內分泌干擾物以及久坐不動之類的生活方式，都是所謂精子危機的造成因素。而且越來越多的證據表明，精子數和其他健康狀況一樣，也有可能受到生命早期、甚至是在子宮內所發生情況的影響。
'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.
莫阿爾說：“如果我們配子（不管是精子還是卵子）的產生方式有問題，下一代的健康就有可能受到影響。”
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.
總體上講，男性一毫升精液的精子數在6,000萬以上。只要每毫升精子數大致超過4,000萬，男性就被認爲具有生育能力。即使和某個精子數更高的人相比，其讓伴侶受孕的概率也是一樣的。
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.
但如果低於這個門檻、特別是低於每毫升約2,000萬的密度，那麼他們讓伴侶懷孕的能力就下降了。一對夫妻可能要花一年以上的時間才能懷上孩子──這被稱爲“弱育”(subfertility)問題──他們甚至還有可能根本就懷不上。
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.
並不是生育學領域內所有人都認爲有精子危機存在。批評者說，人羣中的精子密度非常難以測量，原因有很多，首先便是如何找到人羣中具有代表性的男性。比方說，如果是跟蹤那些前往不孕不育醫院就診的男性，那麼跟蹤結果就有可能一邊倒。捐精者也不能準確代表一個地區內的全部男性。近期曾有一些研究考察了申請參軍的年輕男性，但這種研究的參與率往往不高。
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，由於禁慾時間、陰囊溫度和季節等一個或多個直接的環境因素，也可能引起測量誤差。
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.
德國明斯特大學(University of Munster)生殖醫學與男科學中心(Center for Reproductive Medicine and Andrology)主任斯特凡・舒拉特(Stefan Schlatt)認爲，並不存在一場世界範圍的精子危機。舒拉特說，即使精子數確實是隨着時間的推移而下降了，卻也不會知道弱育或不育範疇的男性數量增加了多少。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.
但據愛丁堡大學(University of Edinburgh)男性生育健康專家理查德・夏普(Richard Sharpe)說，在北歐展開的聯合調查發現，精子數低到影響生育的男性比例已高達五分之一。
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.
關鍵之處可能在於支持細胞（Sertoli cell，又譯塞託利細胞），這種細胞在睾丸內精子細胞發育成精子的10周過程中爲它們提供支持。每一個支持細胞只能支持一定數量的精子細胞，所以支持細胞數量在事實上設定了男性精子產量的上限。
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.
支持細胞似乎是在男孩出生的前後六個月內增殖。夏普說，外部因素可以降低精子產量，但似乎沒有任何外部因素可以將產量提高到支持細胞數量設定的上限之上。
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.
莫阿爾在倫敦年會上提交了一份研究報告。在這項研究中，她和同事考察了法國一家名叫“Fivnat”，負責人工生殖技術統計的專業機構收集的數據。樣品由2.6萬名男性組成；他們的女性伴侶已知不育，並從1989年到2005年在全國各地的醫院接受了不孕不育治療。這些男性是否不育是未知的，因此其代表性被認爲優於那些側重於尋求不孕不育治療的男性的研究。
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.
這些男性的精液質量在不同的實驗室做了兩次檢測，測量了精子的數量、活力和形狀。研究人員取了兩組樣本的平均數，以得到一個更可靠的數字，從而把年齡和季節因素考慮進去。莫阿爾還說，這段時期內法國各地的檢測方法、特別是測量精子數量和活力的檢測方法並沒有很大的變化。檢測方法的改變是對這類長期研究的常見批評。
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.
他們發現，在這17年的研究期內，男性精子密度下降接近三分之一，即一年下降1.9%。1989年，35歲男性的平均精子密度爲每毫升7,360萬，遠高於弱育的門檻；2005年則已下降到每毫升4,940萬。研究結果於2012年12月發表在《人類生殖》(Human Reproduction)雜誌上。
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.
越來越多的證據表明，生命早期的影響會帶來不同。一些研究人員說，在生命脆弱期，可能是妊娠八週到14周之間，其受到的影響是不可逆的。與精子數下降相關性最大的因素之一，就是母親孕期吸菸。
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.
一項名爲“Raine”的研究調查了將近2,000名男性，他們參與調查的時候是嬰兒期，現在已經20歲出頭。在這項研究中，睾丸的大小與精子總量有關，而在胎齡不足、童年時期過重或過輕、或母親孕期吸菸的男孩身上，精子數更低的概率更大。
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.
根據西澳大學(University of Western Australia)生殖醫學教授羅傑・哈特(Roger Hart)在年會上提交的數據，男性自己當期吸食大麻也被發現跟精子數更低有關。
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.
有些影響精子的因素可能是不可逆的。另外一些研究發現，年輕男性腹部脂肪的多少與其睾丸激素水平有關，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:
愛丁堡大學的夏普說：“通過在孕期採用健康、均衡的飲食和生活方式，你可以給發育中的嬰兒最好的人生開端，從而將未來罹患疾病的風險最小化。”他說：“如果生的是男孩，那麼這樣做還會確保他的精子數，進而保證他的生育能力無論如何都不會遭到削弱。”
