Exposure to estrogen as a result of not having reached menopause, having more children and more reproductive years, and using HT and HC, was associated with larger gray matter volumes in midlife women.
Researchers found no association between reproductive history events and people's memory scores, but people who scored better did have more gray matter compared to those that scored less.
Dr. Sara Imarisio, head of research at Alzheimer's Research UK, said: "Two thirds of people with dementia are women and while some of this difference is explained by women living longer, research has also implicated hormones like estrogen. The start of periods, having children, and menopause are significant events in many women's lives and it's important to understand how these biological changes might affect long-term brain health and dementia risk.
"This study linked exposure to estrogen to less brain shrinkage, an indication of lower dementia risk, but this is a small study, and it did not explain the causes for the association. The researchers worked with participants in midlife, a key period for brain health and reducing dementia risk, but as the brain scans were not specific to Alzheimer's disease, we cannot make firm conclusions about risk of developing the condition from this study. Examining the biological pathways through which reproductive history influences cognitive aging and Alzheimer's disease risk is the next step for researchers to understand this link.
"Alzheimer's disease is caused by a complex mix of age, genetics and lifestyle factors—some of which are in our control to change, and others which aren't. The best current evidence suggests that not smoking, only drinking within the recommended limits, staying mentally and physically active, eating a balanced diet, and keeping blood pressure and cholesterol levels in check can all help to keep our brains healthy as we age."