研究：生过孩子的女性老得更快

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

一项新研究发现，生过孩子的女性在生理上会比那些没有生过的“更老”。

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.

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.

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.

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.

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.