March 29 (UPI) -- A woman is more likely to develop dementia if she starts her period later, new research shows.
About 42 percent of women who started menstruation later, began menopause earlier or had a hysterectomy in life developed dementia when they got older, according to a study published Wednesday in Neurology.
"Since women are 50 percent more likely to develop dementia over their lifetimes than men, it's important to study any risk factors that are specific to women that could eventually lead us to potential points of intervention," Paola Gilsanz, a researcher at Kaiser Permanente and study author, in a news release.
Researchers looked at the medical records of more than 6,100 women who were members of Kaiser Permenente Northern California.
For participants, the average age of first period was 13, average age of menopause was 45 and average total number of reproductive years was 32, and 34 percent reported a hysterectomy. When looking at only women who did not have hysterectomy, average age of menopause was 47 and average total number of reproductive years was 34.
When women start their menstrual cycle at age 16, it increased their risk for dementia by 23 percent -- compared to females who started at age 13.
The researchers also discovered that women who experienced natural menopause before age 47 had a 19 percent higher risk of dementia than women who started menopause at age 47 or older.
The average study participant had her first period at age 13 and began menopause at 45, giving her a total of 32 reproductive years. Those women had a 20 higher risk of dementia.
Also, 34 percent of the women reported having a hysterectomy.
Women who went without a hysterectomy began menopause at age 47 and had 34 reproductive years.
"Estrogen levels can go up and down throughout a woman's lifetime," Gilsanz said. "Our results show that less exposure to estrogen over the course of a lifetime is linked to an increased risk of dementia. However, while our study was large, we did not have enough data to account for other factors that could affect estrogen levels, like pregnancies, hormone replacement therapy or birth control, so more research is needed."