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Though it’s known as the “good cholesterol,” higher levels of HDL-C have been shown to correlate with . A new study in the  might explain why.

Once women reach the menopause transition, it’s a matter of the quality, rather than quantity, of the total cholesterol carried by HDL particles circulating in a woman’s bloodstream. And that quality declines over time, according to a research team led by a Samar El Khoudary, professor of epidemiology in the School of Public Health.

HDL particles vary in their size, composition and level of functioning. The team measured these features in the blood of 503 women from the Study of Women’s Health Across the Nation () HDL ancillary study. The researchers found that, over time, the number of larger HDL particles in the women’s bodies increased — and these larger particles, unfortunately, did not function as well as their smaller counterparts. 

The researchers conducted repeated assessments of study participants’ cognitive function from 2000 to 2016, comparing the data to changes in the women’s HDL particles, composition and function as they aged.

“We were able to show that as early as midlife, women who have more of the smaller-sized particles and those whose particles’ concentrations of phospholipids increased over the menopause transition are more likely to experience better episodic memory later in life,” said El Khoudary, adding that loss of working memory is the first sign of Alzheimer’s disease.

Previously, her team has shown that health behaviors — including physical, a balanced diet and good sleep  — work to , for example by adding more of the phospholipid-rich particles in the bloodstream.

“That’s the good news in this developing picture of brain health and the ‘not-so-good-after-all’ cholesterol,” said El Khoudary. “Even though higher levels of HDL-C may not be protective as you get older, there are things you can do that might help, even as early as your 40s.”

Meiyuzhen Qi, post-doctoral researcher in the Department of Epidemiology at 51��Ʒ��Ƶ Public Health, is first author of this study. Additional co-authors include scientists from the University of Pennsylvania, Rush University, University of California Los Angeles, Albert Einstein College of Medicine, University of Michigan and University of Massachusetts.