A woman’s brain may start to decline in function earlier in life than experts previously realized.

Researchers analyzed data on memory and processing speed tests on more than 2,000 middle-aged women, finding that their episodic memory — relating to past events — declined about 2 percent over the course of 10 years, according to a study in PLoS One. Meanwhile, their brains’ processing speed slowed 5 percent in that time. The authors called both those changes “substantial.”

The data on speed was based on tests in which the women had to match numbers and symbols in a certain amount of time and the data on memory came from tests in which they were read a story and then had to recall information from it both immediately and then 10 minutes later.

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Most of the women studied were past menopause, with an average age of 54. According to the researchers, most previous studies have looked at cognitive aging in women in their 60s or older, so that age group is significant.

But don’t panic: “A decline in processing speed in midlife is not a harbinger of declines in other domains of functioning,” the study explains. People age differently and the body can compensate to “ameliorate the impact of cognitive aging on functioning and well-being.”

The authors call for more research to determine what exactly affects how quickly our brain function declines, with the goal of developing treatments that will slow the process.

The University of California, Los Angeles, said in a statement that the new findings are more precise than those from many previous studies because they adjusted for an element called “practice effects,” in which people test better shortly after learning about how to take the test administered. The researchers disregarded the women’s first two tests during the study period because the practice effects are greatest between the first and second tests.

“Women in their 40s and 50s who find they are forgetting things more often or think they are slower to react may only be experiencing usual aging, analogous to ... other declines that we all experience in midlife,” UCLA said.

Source: Greendale GA, Karlamangla AS, Lachman ME, Han W, Huang M. Evidence for Cognitive Aging in Midlife Women: Study of Women’s Health Across the Nation. PLoS One. 2017.

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