Does parity matter in women’s risk of dementia? A COSMIC collaboration cohort study
Authors: Bae Jong Bin , Lipnicki Darren M. , Han Ji Won , Sachdev Perminder S. , Kim Tae Hui , Kwak Kyung Phil , Kim Bong Jo , Kim Shin Gyeom , Kim Jeong Lan , Moon Seok Woo , Park Joon Hyuk , Ryu Seung-Ho , Youn Jong Chul , Lee Dong Young , Lee Dong Woo , Lee Seok Bum , Lee Jung Jae , Jhoo Jin Hyeong , Llibre-Rodriguez Juan J. , Llibre-Guerra Jorge J. , Valhuerdi-Cepero Adolfo J. , Ritchie Karen , Ancelin Marie-Laure , Carriere Isabelle , Skoog Ingmar , Najar Jenna , Sterner Therese Rydberg , Scarmeas Nikolaos , Yannakoulia Mary , Dardiotis Efthimios , Meguro Kenichi , Kasai Mari , Nakamura Kei , Riedel-Heller Steffi , Roehr Susanne , Pabst Alexander , van Boxtel Martin , Köhler Sebastian , Ding Ding , Zhao Qianhua , Liang Xiaoniu , Scazufca Marcia , Lobo Antonio , De-la-Cámara Concepción , Lobo Elena , Kim Ki Woong ,   for Cohort Studies of Memory in an International Consortium (COSMIC), Sachdev Perminder S. , Lipnicki Darren M. , Makkar Steve R. , Crawford John D. , Thalamuthu Anbupalam , Kochan Nicole A. , Leung Yvonne , Lo Jessica W. , Turana Yuda , Castro-Costa Erico , Larijani Bagher , Nabipour Iraj , Rockwood Kenneth , Shifu Xiao , Lipton Richard B. , Katz Mindy J. , Preux Pierre-Marie , Guerchet Maëlenn , Lam Linda , Skoog Ingmar , Ninimiya Toshiharu , Walker Richard , Hendrie Hugh , Guaita Antonio , Chen Liang-Kung , Shahar Suzana , Dominguez Jacqueline , Krishna Murali , Ganguli Mary , Anstey Kaarin J. , Crowe Michael , Haan Mary N. , Kumagai Shuzo , Ng Tze Pin , Brodaty Henry , Meguro Kenichi , Mayeux Richard , Schupf Nicole , Sachdev Perminder , Ganguli Mary , Petersen Ronald , Lipton Richard , Lowe Edwin S. , Ritchie Karen , Kim Ki-Woong , Jorm Louisa , Brodaty Henry 
Published: August 2020

Abstract
Background
Dementia shows sex difference in its epidemiology. Childbirth, a distinctive experience of women, is associated with the risk for various diseases. However, its association with the risk of dementia in women has rarely been studied.

Methods
We harmonized and pooled baseline data from 11 population-based cohorts from 11 countries over 3 continents, including 14,792 women aged 60 years or older. We investigated the association between parity and the risk of dementia using logistic regression models that adjusted for age, educational level, hypertension, diabetes mellitus, and cohort, with additional analyses by region and dementia subtype.

Results
Across all cohorts, grand multiparous (5 or more childbirths) women had a 47% greater risk of dementia than primiparous (1 childbirth) women (odds ratio [OR] = 1.47, 95% confidence interval [CI] = 1.10–1.94), while nulliparous (no childbirth) women and women with 2 to 4 childbirths showed a comparable dementia risk to primiparous women. However, there were differences associated with region and dementia subtype. Compared to women with 1 to 4 childbirths, grand multiparous women showed a higher risk of dementia in Europe (OR = 2.99, 95% CI = 1.38–6.47) and Latin America (OR = 1.49, 95% CI = 1.04–2.12), while nulliparous women showed a higher dementia risk in Asia (OR = 2.15, 95% CI = 1.33–3.47). Grand multiparity was associated with 6.9-fold higher risk of vascular dementia in Europe (OR = 6.86, 95% CI = 1.81–26.08), whereas nulliparity was associated with a higher risk of Alzheimer disease (OR = 1.91, 95% CI 1.07–3.39) and non-Alzheimer non-vascular dementia (OR = 3.47, 95% CI = 1.44–8.35) in Asia.

Conclusion
Parity is associated with women’s risk of dementia, though this is not uniform across regions and dementia subtypes.