Women who had longer reproductive periods during their lifetimes were found to have a greater risk of dementia in older age compared with those who had shorter reproductive periods, according to a population-based study published in Alzheimer's & Dementia.1,2

In the study, the authors explained that the reproductive period spans the years between menarche, which is the onset of menstruation, and menopause, which is the end of menstruation.1

"Our results may explain why women have a higher risk of developing dementia and Alzheimer's disease than men after age 85, and provide further support for the hypothesis that estrogen affect the risk of dementia among women," said Jenna Najar, MD, a doctoral student at Sahlgrenska Academy and researcher at AgeCap, the Centre for Ageing and Health at the University of Gothenburg, in a press release.2

The study participants included 1364 women in Gothenburg, Sweden, who were observed and followed between 1968 and 2012 in 2 population studies known as the Prospective Population-based Study of Women in Gothenburg (PPSW) and the Gothenburg H70 Birth Cohort Studies in Sweden (the H70 studies).1,2

In the study, the women with a shorter reproductive period of 32.6 years or less developed dementia at a rate of 16% (53 of 333 individuals). Those women with a longer reproductive period of 38 years or more developed dementia at a rate of 24% (88 of 364).1,2

With the difference present between each group of women, the authors explained that they observed that the risk for dementia and Alzheimer disease increases successively for each additional year that a woman is fertile.1,2

After adjusting for other factors that could potentially influence the findings, such as educational attainment, physical activity, body mass index, smoking, and cardiovascular disease, the researchers found that the results persisted.1,2

Notably, the authors explained there was no association found between risk of dementia and age at menarche, number of pregnancies, duration of breastfeeding, or exogenous estrogen intake, such as in the form of hormonal replacement therapy (HRT) or oral contraceptives.1,2

Since prior studies had investigated whether estrogen in the form of HRT affects dementia risk, the current study investigated the longterm association between factors connected to endogenous estrogen and dementia specifically.1,2

"What's novel about this study, too, is that we've had access to information about several events in a woman's life that can affect her estrogen levels. Examples are pregnancies, births, and breastfeeding. Being pregnant boosts estrogen levels tremendously; then they decline once the baby is born, and if women breastfeed the levels fall to extremely low levels. The more indicators we capture, the more reliable our results are," Najar said in the press release.2

Additionally, study lead Ingmar Skoog, MD, PhD, professor of psychiatry at Sahlgrenska Academy, University of Gothenburg and head of AgeCap, explained in the press release that varying results for estrogen could be due to estrogen having a protective effect early in life, but then a potentially harmful effect following the onset of the disease.2

However, Skoog noted that the duration of women's reproductive periods is only a single risk factor for dementia among many. The study supports a potential reason as to why women specifically are at a greater risk than men for dementia when they are over the age of 85, which is currently the most common onset age.2

"Most people affected are over 80 and female," Najar said. "As a result of global aging, the number of people affected by dementia will increase. To be able to implement preventive strategies, we need to identify people with an elevated risk of dementia."2

REFERENCES
  1. Najar J, Östling S, Waern M, et al. Reproductive period and dementia: A 44‐year longitudinal population study of Swedish women. Alzheimer's & Dementia. 2020;16(8):1153. doi: 10.1002/alz.12118.
  2. Higher dementia risk in women with prolonged fertility. Gothenburg, Sweden: University of Gothenburg; September 17, 2020. Accessed October 6, 2020. sciencedaily.com/releases/2020/09/200917105419.htm.