Women who get their period later in life may be at a higher risk of developing dementia, according to a study published Wednesday in the journal Neurology. That also could be the case for women who go through menopause earlier, or for women who have a hysterectomy. Researchers examined the medical records of thousands of women who sought medical services at Kaiser Permanente Northern California, and found that when compared to women who got their period at age 13, women who got it at age 16 or older were 23 percent more likely to develop dementia. Reproductive spans of less that 34.4 years were associated with a higher dementia risk (20 percent), as were hysterectomies (8 percent). “Two-thirds of the 5.8 million Americans living with Alzheimer’s are women—and we need know more about why,” Maria C. Carrillo, Chief Science Officer at the Alzheimer’s Association, said in a statement. “Lifelong differences in women may affect their risk or protect them from dementia, and we need more research to determine why this is the case.”