When it comes to reducing stroke risk among women, new research suggests that the more estrogen a woman is exposed to over the course of her life, the better.
The finding follows nearly a decade spent tracking stroke risk among roughly 123,000 Chinese postmenopausal women.
In the end, investigators concluded that those who had a relatively long reproductive period before menopause appeared to face a lower risk for both an ischemic stroke and a hemorrhagic stroke.
An ischemic stroke is the most common form of stroke, brought on by blood flow blockage to the brain. A hemorrhagic stroke is brought on by bleeding in the brain.
“These results were unexpected and provide new insights into the associations between reproductive factors and the risk of stroke,” said study author Peige Song, a researcher with Zhejiang University’s School of Public Health in Hangzhou, China.
To explore a possible protective link between estrogen and stroke risk, Song and her team focused on a pool of women between the ages of 40 and 79. None had a history of stroke when they had first enrolled in a prior Chinese study between 2004 and 2008.
The team first analyzed study enrollment information regarding the specific length of each woman’s overall reproductive life span leading up to menopause.
Song and her colleagues also took into account how often participants had a child and/or whether or not (and for how long) they took birth control pills, as both typically drive up estrogen levels. Breastfeeding patterns -- which tend to drive down estrogen exposure -- were also noted.
Additional information was gathered on alcohol and smoking habits, overall medical background, and each woman’s pregnancy, miscarriage and oral contraceptive history.
In turn, the team went on to track study participants for roughly nine years, during which time a little more than 15,000 strokes occurred. The vast majority (12,000) were ischemic.
Participants were then divided into four groups ranging from the shortest amount of time between first menstruation and menopause (31 years) and the longest amount of time (36 years).
After stacking each group up against stroke incidence, the team found that women in the longest estrogen exposure group had a 5% lower risk for ischemic stroke and a 13% lower risk for a hemorrhage stroke, compared with women in the shortest exposure group.
The findings took into account a wide range of other factors that can heighten stroke risk, including high blood pressure, older age, a sedentary lifestyle and smoking history.
The team also concluded that higher overall estrogen exposure -- beyond simply the number of years between menstruation and menopause -- also contributed to a lower overall stroke risk.
The finding suggests that women who experience more stillbirths, miscarriages or pregnancy terminations might face a higher risk for stroke, while those who take oral contraceptives might see their risk fall.
Still, Song cautioned that on the latter point, the study had only “limited information on oral contraceptive use.”
Similarly, the study collected little information on the degree to which women embarked on hormone replacement therapy (HRT), she added, “so it is unclear whether estrogen replacement therapy would be as protective as a naturally long reproductive cycle,” given that estrogen from HRT is not naturally produced and “cannot be equated to the natural hormone in the body.”
In fact, the Cleveland Clinic highlights mixed findings on this question, citing multiple investigations that have found that HRT may actually drive up a woman’s risk for both stroke and heart attacks.
Song also underscored the fact that her team’s study largely relied on each participant’s ability to recall their prior experiences and lifestyle choices, and such recall may not always be accurate.
The upshot, she stressed, is that “further research is necessary to fully understand the relationship between estrogen and stroke risk.”
In the meantime, however, Song touched on some ideas as to why greater estrogen exposure might offer women protection against stroke.
For one, she said, estrogen has been shown to have “neuroprotective properties,” which help limit the risk for cellular malfunction while preserving nervous system health.
And at the same time, Song said, estrogen “has been shown to have both short-term and long-term impacts on blood vessel walls,” helping to relax and widen blood vessels, improve blood flow and thereby lower the risk for ischemic stroke in particular.
The study findings were published Feb. 1 in the journal Neurology.
There's more on women and stroke at U.S. Centers for Disease Control and Prevention.
SOURCES: Peige Song, PhD, researcher, Zhejiang University's School of Public Health, Hangzhou, China; Neurology, Feb. 1, 2023