USC Study Suggests Low Levels Of Dietary Nutrient Lutein, Found In Leafy Greens, Linked To Thickening In Neck Arteries

The study on lutein and atherosclerosis—the common condition of buildup on inner artery walls that can lead to heart attacks and strokes—helps explain why fruit- and vegetable-rich diets seem to protect cardiovascular health, the researchers report in the June 19 issue of the journal Circulation. Atherosclerosis accounts for more than 1.5 million heart attacks and 600,000 strokes every year in the U.S.

"Scientific knowledge of the long-term effects of diet on cardiovascular disease is still rudimentary, but there is mounting evidence that increased intake of vegetables and fruits is protective against cardiovascular disease," says James Dwyer, Ph.D., USC professor of preventive medicine. "Unlike the use of supplements, such as beta carotene, increased intake of vegetables and fruit is also very unlikely to yield surprise adverse effects."

Dwyer continues: "The importance of our findings concerning lutein and atherosclerosis is that we may have identified one of the many components of vegetables that account for the protective effects of vegetables."

Findings suggest that increased intake of the dark green leafy vegetables, such spinach, kale and collard greens, may prevent—or at least slow—the progression of the underlying disease that leads to most heart attacks and strokes. Fortunately, such foods can easily be incorporated into a normal American diet.

"They can be eaten in raw in salads, or they can be cooked by themselves or as additions to many recipes," Dwyer says. "Cooking these greens may reduce the bioavailability of the lutein somewhat, but most of the impact on blood levels of lutein is retained after they are cooked."

Dwyer and colleagues conducted their study in three parts. They looked at the relationship between study participants’ artery wall thickness and lutein consumption, they examined cell samples from human artery walls, and they compared the arteries of mice that had eaten lutein to those of mice that had not eaten lutein.

In the first part of the study, researchers monitored 480 men and women between ages 40 and 60 participating in the Los Angeles Atherosclerosis Study. Participants had no history of heart disease or stroke. Using ultrasound technology, the researchers measured the thickness of the walls of the carotid (neck) arteries once at the beginning of the study and again 18 months later. They also measured levels of lutein in participants’ blood over the same time span.

They found that people whose blood carried the highest levels of lutein averaged only a 0.004 mm increase in the artery thickness over 18 months. In those with the lowest levels of lutein, artery wall thickness increased an average of 0.021 mm.

The second part of the study explored how lutein may protect cells in artery walls. Researchers grew layers of cells from human arteries in a lab, then exposed them to various combinations of lutein and LDL (or low-density lipoprotein, the so-called "bad" cholesterol known to promote atherosclerosis).

They found that arterial cell layers treated with lutein were less prone to starting a process of inflammation related to LDL that leads to atherosclerotic plaque. The more the inner layers of the artery wall were exposed to lutein, the more they appeared protected.

In the third portion of the study, done with mice, the team found that adding lutein to the diet resulted in the mice having significantly smaller atherosclerotic lesions compared to mice that had no lutein supplementation.

Dwyer and colleagues caution that more research must be done—from epidemiological studies to randomized trials testing specific diets—to better determine the effect of lutein from food or in supplements on human atherosclerosis and cardiovascular disease.

Lutein is in a class of compounds known as carotenoids, which are found in many foods. Other studies have suggested lutein may be important in eye health. However, another carotenoid tested in the study, beta carotene, was not found to help protect against atherosclerosis—a finding consistent with previous studies.