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Having last baby after 35? Mental sharpness increases
This is the first study to investigate the association between age at last pregnancy, which can be a marker of a later surge of pregnancy-related hormones, and cognitive function in later life, said Roksana Karim, lead author of the study and assistant professor of clinical preventive medicine at the Keck School of Medicine of USC.
"Based on the findings, we would certainly not recommend that women wait until they're 35 to close their family, but the study provides strong evidence that there is a positive association between later age at last pregnancy and late-life cognition."
The study, published this month in the Journal of the American Geriatrics Society, includes 830 women who, on average, were 60 years old. The data was adjusted for age, race and ethnicity, income, and education.
Participants were given a series of tests that included assessments of verbal memory (remembering a list of words or retelling a story after some distraction), psychomotor speed, attention and concentration, planning, visual perception, and memory.
The study found that other reproductive events were also important to later life cognition. More time between first and last period — longer reproductive life — proved valuable for executive function.
"Starting your period early means you have higher levels of the female sex hormone being produced by the ovaries," Karim said. "Girls are receiving the optimal levels early, so it's possible that their brain structures are better developed compared to those who are exposed to estrogen levels associated with menstrual cycles at a later age."
Use of the pill or other hormonal contraceptives for at least 10 years was beneficial for verbal memory and critical thinking ability.
"Oral contraceptives maintain and sustain a stable level of sex hormones in our blood stream," Karim said. "Stable is good."
"The finding that even incomplete pregnancies are beneficial was novel and surprising," said Wendy Mack, the study's senior author and professor of preventive medicine at the Keck School of Medicine. "In general, our findings are intriguing and are supported by other clinical studies and animal studies."
In humans, however, previous studies have shown that "pregnancy brain" exists, meaning researchers found that pregnant women have poorer verbal memory, word fluency and word-list learning when compared to non-pregnant women.
"The issue is the human studies haven't followed women for the long term," Mack said. "They just looked at women during pregnancy. We are not sure if we can expect to detect a positive estrogen effect at that point, as the many bodily changes and psycho-social stressors during pregnancy also can impact women's cognitive and emotional functions."
Participants — Naturally menopausal women
In this sample of healthy postmenopausal women, reproductive life events related to sex hormones, including earlier age at menarche, later age at last pregnancy, longer reproductive period, and use of oral contraceptives are positively related to aspects of cognition in later life.
The research was supported by the National Institutes of Health and included data from two clinical trials: Women's Isoflavone Soy Health and Early vs. Late Intervention Trial of Estradiol.
A study provides evidence of the positive association between
later age at last pregnancy and improved late-life cognition.
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