一项新的研究表明：生过孩子的女人比那些没有生过孩子的女人在生理上更老！

Women who give birth may be biologically "older" than women who don't, a new study suggests.

针对这项研究，研究人员分析了来自于1556名年龄在22岁到44岁之间的美国女性的血液样本，这项调查从1999年持续到2002年。

For the study, the researchers analyzed information from 1,556 US women ages 20 to 44 who took part in a national survey from 1999 to 2002, which involved giving blood samples.

研究人员看着基因物质进入女性的细胞核，尤其是他们的染色体的长度。这些物质就像是染色体末端的帽子一样，保护染色体免受伤害。研究表明染色体会自然变短当人们年龄增长的时候，但是其结构变短的频率每个人有所不同。一个人的染色体越长，在假设上细胞的分裂次数更多。因此，染色体被认为是生理年龄的标志，不过，心理年龄指的是个人的细胞年龄而不是个体的时间年龄。

The researchers looked at the genetic material inside the women's cells, specifically the length of their telomeres. These are caps on the ends of chromosomes that protect the chromosomes from damage. Telomeres naturally shorten as people age, but the structures don't shorten at the same rate in every person. The longer a person's telomeres are, the more times their cells could hypothetically still divide, research has shown. Thus, telomeres are considered a marker of biological age — that is, the age of a person's cells, rather than the individual's chronological age.

在调查中，至少生过一个孩子的女性染色体的长度平均比没有生过孩子的女性染色体短4%。这个结果是研究人员在考虑了其他可能影响染色体长度的因素之后得出的，包括女性的时间年龄、体质指数和抽烟习惯。

Women in the survey who said they'd given birth to at least one child had telomeres that were about 4 percent shorter, on average, than those of women who'd never given birth. The findings held even after the researchers took into account other factors that could affect telomere length, including the women's chronological age, body mass index and smoking habits.

这些结果表明生育历史可能和染色体的缩减相关，研究人员把这一结论写在了丹佛举行的美国公众健康协会会议提案中。

These findings suggest that a "history of live birth may be associated with shorter telomeres," the researchers wrote in their abstract, which was presented at the meeting of the American Public Health Association in Denver.

研究人员说，这项研究并不是为了确定女性是否生孩子与染色体缩短之间的关系背后的原因。但是，科学家认为有一个原因和染色体的缩短相关，那就是生孩子会使压力水平上升，高压和染色体的缩短相关。

The study was not designed to determine the reason behind the link, the researchers said. But one hypothesis is that having children increases stress levels, and high stress has been linked with shorter telomeres, the scientists said

“怀孕、生育和抚养孩子可能会增加慢性压力，通过炎症通道导致染色体长度的缩短。”梅林大学环境和生殖流行病专家教授助理Anna Pollack 说道。然而，因为这项调查以一个单一论点及时实施了，所以研究人员不能确定在女性生命中生育和染色体缩短哪个先出现，Pollack 说道。也有可能因为一些现在还不确定的原因，那些有着较短染色体的女性比拥有较长染色体的女性更容易怀孕。

"It is possible that pregnancy, birth and child-rearing can induce chronic stress, leading to shorter telomere length perhaps through an inflammatory pathway," said study researcher Anna Pollack, an assistant professor and environmental and reproductive epidemiologist at George Mason University. However, because the survey was conducted at a single point in time, the researchers cannot determine which came first in the women's lives — giving birth or having shorter telomeres, Pollack said. It's also possible that for some yet-unknown reason, women with shorter telomeres are more likely than women with longer ones to have children, Pollack said.

她认为需要进行更多的研究对女性进行长时间的跟踪调查，测量女性怀孕前、怀孕中、怀孕后的染色体的长度。

More studies are needed that follow women over time and measure the length of their telomeres before, during and after pregnancy, she said.

观察染色体在女性怀孕中、怀孕后和孩子抚养过程中的程度变化，以及这些变化和那些未怀孕女性的比较将会非常有趣。

"It would be interesting to see how telomere length changes during pregnancy, after birth and during the child-rearing years, and how these changes compare to women who do not have children," Pollack said.

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