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For the most part, good cholesterol decreases the risk of heart attacks or strokes, whereas bad cholesterol increases the risk. A complex study looked more closely at the different types of cholesterol, and how they could affect the risk of disease in post-menopausal women.
Cholesterol is a type of fat that can build up as a plaque in the wall of blood vessels. As the plaque grows, it can narrow or even completely block the vessel. If such a blockage occurs in the arteries of the heart it could cause a heart attack. If the blockage occurred in the brain, it could cause a stroke. But not all cholesterol is equally likely to end up in a plaque. In fact, people with high levels of ‘
’ tend to have fewer and smaller plaques.
Cholesterol and other fats are transported through the bloodstream in small globules that are shaped by different types of proteins. Some of these types of globules tend to pick up cholesterol from arterial plaques and return it to the liver for safe storage. Cholesterol in these types of globules is ‘good cholesterol’. On blood test results, this is usually shown as HDL (high-density lipoprotein) cholesterol. This is in contrast to ‘bad cholesterol’, which blood tests usually show as LDL (low-density lipoprotein) cholesterol.
“Good” cholesterol may not be good for everyone
HDL, known as the “good” cholesterol may not be equally good for everyone. For example, some studies have found that older women with high HDL cholesterol may actually have an increased risk of stroke. Some researchers think that HDL cholesterol is too crude a measure and that the health benefits of HDL are better measured by the number and size of these HDL globules, rather than just their cholesterol content. There are laboratory methods to measure globule size and number, but these tests are rarely performed in medical clinics.
A group of American researchers recently compared measurements of HDL good cholesterol and the size and number of HDL globules in women who were close to, or past, the age of menopause. They sought to determine which of these variables were most strongly associated with the formation of arterial plaques. They published the results of this complex study in the journal Arteriosclerosis, Thrombosis, and Vascular Biology.
Comparing the size and number of cholesterol-containing globules to arterial plaques
Researchers took ultrasound images of the carotid artery in more than 1,000 women. They used these images to count the number of plaques and measure the thickness of the artery wall. Arterial wall thickness is another measure of arterial health; arterial walls which have picked up a lot of cholesterol tend to be more inflamed and thicker than healthier arterials walls.They also took blood samples to measure HDL good cholesterol and the number and size of the HDL globules.
Women with more HDL ‘good’ cholesterol were more likely to have arterial plaques
In women with the same number of HDL globules, those with higher levels of HDL ‘good’ cholesterol were more likely to have arterial plaques. However, it was necessary to measure both HDL cholesterol and the number of HDL globules to detect this effect. Just looking at HDL cholesterol on its own didn’t reveal any effect on plaque formation. The size of the HDL globules did not affect the likelihood of having arterial plaques.
Women with more HDL globules had healthier arterial walls
Women with higher HDL (good) cholesterol or a greater number of HDL globules tended to have thinner arterial walls, a sign of good arterial health. This result would seem to contradict what the researchers found for plaques.
This apparent contradiction was explained by looking at HDL cholesterol and globule numbers together. In women with the same level of HDL cholesterol, those with a greater number of HDL globules had thinner, healthier, arterial walls. However, in women with the same number of HDL globules, the amount of HDL cholesterol had no effect on arterial wall thickness. Therefore the number of HDL globules is a better predictor of arterial health than HDL ‘(good) cholesterol.
Women with smaller HDL globules had healthier arterial walls
Considered independently, having greater numbers of large or small HDL globules were both associated with thinner, healthier, arterial walls. However, in women with the same number of large HDL globules, those with a greater number of small globules had thinner, healthier, arterial walls. In contrast, in women with the same number of small HDL globules, the number of large HDL globules had no effect on arterial wall thickness. This implies that smaller HDL globules are associated with improved arterial health and larger HDL globules with worse arterial health.
The effect of HDL globule size changes with age
The researchers looked at how aging affects the relationship between HDL globule size and arterial thickness. One year after menopause, women with a greater number of large HDL globules tended to have thicker arterial walls. However, this relationship tended to change as women aged. In women who were 32 years past menopause, those women with the greatest number of large HDL globules tended to have thinner arterial walls.
‘Good’ cholesterol: not so simple
The complex results of this study show that there is still much to be learned about blood cholesterol measurements and what they mean for your health. Measuring the size and number of cholesterol globules may allow doctors to better understand who is at risk of strokes and heart disease; however, more studies are needed to understand how the characteristics of cholesterol-containing globules relate to disease risk. This should include studies that track changes to HDL and arterial plaques as people age.
Written by Bryan Hughes, PhD
Reference: El Khoudary, S. R., Ceponiene, I., Samargandy, S., Stein, J. H., Li, D., Tattersall, M. C. & Budoff, M. J. HDL (High-Density Lipoprotein) Metrics and Atherosclerotic Risk in Women: Do Menopause Characteristics Matter? MESA. Arterioscler Thromb Vasc Biol (2018) https://www.ahajournals.org/doi/10.1161/ATVBAHA.118.311017