Objective: While exposure to endogenous estrogen may be associated with better cognitive performance, it is still unclear whether it has an association with mild cognitive impairment (MCI) or dementia. The aim of this study was to clarify the effects of reproductive history, as a surrogate marker of exposure to endogenous estrogen, on the risk of cognitive impairment (MCI or dementia) in women. Study design: A total of 747 women aged 40–59 years in the Saku area (Nagano Prefecture) were followed as part of the Japan Public Health Center-based Prospective (JPHC) Study, which started in 1990. Participants had undergone a mental health examination in 2014–2015. Main outcome measures: We used multiple logistic regression to analyze the association between reproductive history, obtained at baseline and 10-year follow-up, with current cognitive impairment diagnosed by a trained psychiatrist, adjusting for various lifestyle factors. Results: Among 670 eligible women, current cognitive impairment was diagnosed in 227, 196 of whom had MCI and 31 dementia. A longer reproductive period had a significantly inverse association with cognitive impairment (P-trend = 0.032). In particular, women with a reproductive period ≥38 years compared with ≤33 years had a significantly lower risk of cognitive impairment (multivariable adjusted odds ratio=0.62, 95% confidence interval=0.40–0.96). Conclusions: A longer reproductive period was associated with a lower risk of cognitive impairment, which suggests that a longer exposure to endogenous estrogen may have a protective effect against cognitive impairment.
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