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The reproductive life span of women in the United States has increased over the past 6 decades, as menarche has been starting earlier and menopause coming later, according to an observational study.

In 7,773 women followed from 1959 to 2018, the mean age at menopause increased by 1.5 years, from 48.4 to 49.9, and the mean age at menarche declined by 0.8 years, from 13.5 to 12.7 (P<0.001 for both trends), reported Duke Appiah, PhD, of Texas Tech University Health Sciences Center in Lubbock, and colleagues.

As shown in their study published as a research letter online in , the mean reproductive life span of the women during the study increased by 2.1 years, from 35 to 37.1 years (P<0.001).

"The increase in reproductive life span was driven both by increasing age at natural menopause and earlier age at menarche," the researchers wrote. "Sociodemographic, lifestyle, and behavior factors were significantly associated with age at natural menopause and reproductive life span. Additional potential contributing factors may include improved access to health care, nutrition, and environmental factors."

Factors associated with earlier age at natural menopause and shorter reproductive life span included the following:

• Black race (versus white): OR 0.85, 95% CI 0.72-1.01, P=0.006

• Hispanic race (versus white): OR 0.70, 95% CI 0.55-0.88, P=0.006

• Poverty: OR 0.83, 95% CI 0.71-0.97, P=0.02

• Current smoker: OR 0.57, 95% CI 0.47-0.69, P<0.001

• Former smoker: OR 0.75, 95% CI 0.63-0.88, P<0.001

• Ever use of hormone therapy: OR 0.87, 95% CI 0.75-1.00, P=0.05

Factors associated with later age at natural menopause and a longer reproductive life span included having more than a high school education (OR 1.36, 95% CI 1.15-1.60, P<.001) and use of oral contraceptives (OR 1.26, 95% CI 1.08-1.48, P=0.005), the study found.

"Available evidence links later age at natural menopause with reduced all-cause and cardiovascular mortality but increased risk of breast, endometrial, and ovarian cancers," the investigators wrote. "Whether the 1.5-year increase in age at natural menopause over a 60-year time span has clinical significance for women's health apart from reproduction is unknown."

Asked for her perspective, Stephanie Faubion, MD, medical director of the North American Menopause Society (NAMS), who was not involved with the study, said the changes in the study may be due to better education and healthcare.

"What are the implications of these changes? It's hard to say for the individual woman, but hormones influence health in many ways. Risk of heart disease, osteoporosis, cardiovascular mortality, and all-cause mortality are typically lower with a longer reproductive life span while breast cancer risk may be higher," Faubion told 名媛直播 via email.

She noted that a , which examined trends in U.S. women from 1912 to 1969, reported similar results.

In the current study, Appiah and colleagues analyzed survey data from the National Health Examination Survey (1959-1962) through the National Health and Nutrition Examination Survey for 2017-2018. The study included 7,773 women ages 40 to 74 at the time of the survey who underwent natural menopause and had data for age at menarche.

Excluded were women with menopause due to medical treatment or other reasons; women who underwent menopause before the age of 40 or after the age of 62 (because pathologic conditions may have influenced the occurrence of menopause at such ages); and women reporting a race/ethnicity other than Black, white, or Hispanic.

The researchers examined trends in age at natural menopause and reproductive life span over time with linear regression models, using ordinal logistic regression to evaluate factors associated with higher age at menopause and longer reproductive life span.

Limitations of the study, the team said, included its repeated cross sectional design, the relatively small sample size, and the potential for recall bias in self-reported age at menarche and menopause. However, "moderate reliability in the recall of these events after several years has been reported," the researchers noted.

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