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The study, of nearly 1,400 postmenopausal women, found that those with higher HDL levels were more likely to show "plaques" in their carotid arteries. Those arteries supply blood to the brain, and plaque buildup there signals an increased risk of both stroke and heart disease.
"We used to think, the higher the better," said Dr. Karol Watson, director of the Women's Heart Health Program at the University of California, Los Angeles. "But we've been re-thinking HDL in recent years."
Watson, who was not connected to the study, is also a member of the American College of Cardiology's Prevention of Cardiovascular Diseases Section Leadership Council.
She said "everyone agrees" that low HDL -- below 40 mg/dL -- is bad.
But studies have also found that very high HDL is linked to trouble, too. For example, a 2016 study of over 630,000 people found that women and men with very high HDL -- above 90 mg/dL -- were more likely to die (of non-cardiovascular causes) during the study period than those whose HDL was in the middle of the pack.
But, Watson said, research suggests that HDL function can go awry when its environment is not ideal -- such as when a person is obese or has diabetes or other health conditions causing chronic inflammation in the blood vessels.
"HDL seems to be like a chameleon, changing based on its surroundings," Watson explained.
That general idea may explain what was seen in this study, according to lead researcher Samar El Khoudary, an associate professor at the University of Pittsburgh's School of Public Health.
During the menopause transition, she said, women see a sharp drop in estrogen, a heart-protecting hormone. They also go through changes in body fat distribution, blood fats and other metabolic processes; that might lead to chronic inflammation that could alter the quality of HDL particles.
So a higher HDL level is "not necessarily cardio-protective," El Khoudary said. But, she added, it's not necessarily bad, either.
It's important to look at the whole picture, she said. If, for example, a woman is normal weight, exercises, and does not have heart risk factors like high LDL cholesterol (the "bad" kind) or diabetes, a high HDL is "probably not something to worry about," El Khoudary said.
Watson agreed. On the other hand, she said, a high HDL level should not make women or their doctors complacent.
"Never ignore a high LDL level just because the HDL is high," Watson said.
The bottom line, according to El Khoudary, is that women should pay even more attention to maintaining a healthy lifestyle as they go through menopause.
On the research end, she said, doctors need more precise measures of HDL function -- not just HDL cholesterol level.
El Khoudary's team also measured the study participants' levels of HDL "particles" -- which carry HDL cholesterol through the blood.
Overall, women with a greater number of "small" HDL particles had a lower risk of plaque buildup. Meanwhile, "large" particles showed a more complicated relationship: When women were just past menopause, those particles were tied to a heightened risk of artery narrowing. But among relatively older women, high numbers of large particles were linked to healthier-looking arteries.
If that all sounds complicated, that's because it is.
For now, Watson said, no one knows whether measuring HDL particles is useful. "Until we understand more, we can't do anything with that information," she said.
How high is "too high" when it comes to HDL? There is no known cutoff, Watson said. In general, she added, there seems to be an HDL "sweet spot" of around 60 to less than 80 mg/dL.
But again, Watson said, you have to look at the whole person: If someone has risk factors for heart disease, a higher HDL number may be misleading.
El Khoudary recently received funding from the U.S. National Institute on Aging to expand on this research.
The findings were published online July 19 in the journal Arteriosclerosis, Thrombosis, and Vascular Biology.
Copyright © 2018 HealthDay. All rights reserved.
SOURCES: Samar El Khoudary, Ph.D., M.P.H., associate professor, epidemiology, University of Pittsburgh School of Public Health; Karol Watson, M.D., director, Barbara Streisand Women's Heart Health Program, University of California, Los Angeles, and member, American College of Cardiology Prevention of Cardiovascular Diseases Section Leadership Council; July 19, 2018, Arteriosclerosis, Thrombosis, and Vascular Biology, online