PR Newswire, 12-01-05
WASHINGTON, Nov 30, 2005 /PRNewswire via COMTEX/ -- There is compelling evidence that lutein and zeaxanthin, nutrients found in green and yellow vegetables and egg yolks, may help protect against the development of age-related eye diseases such as macular degeneration and cataracts. Recent studies suggest that these nutrients may play other protective roles in the body as well, according to researchers who presented at the annual scientific meeting of the Gerontological Society of America.
Lutein (loo' -teen) has become familiar to the public as an ingredient in vitamin supplements formulated for eye health. In foods it is usually found together with its cousin, zeaxanthin (zee-ah-zan'-thin). Both are members of the carotenoid family, a huge rainbow of pigments from the yellow of corn to the red of tomatoes, many of which have been linked to reduced risk for chronic diseases.
Age-Related Eye Diseases
While lutein and zeaxanthin can be found in many body tissues, they are most strikingly accumulated in the eye, where they are highly concentrated in the macula, a small region at the back of the retina that governs the sharpness of visual images. The concentration of these two carotenoids in the macula is 500 times higher than in any other body tissue.
Because of this natural preference by the macula for lutein and zeaxanthin, scientists began to search for evidence that they may play special roles in eye health. Elizabeth Johnson, PhD, an investigator in age-related eye diseases from the USDA Human Nutrition Research Center on Aging at Tufts University, presented a summary of this research.
"Lutein has been strongly implicated as being protective against age-related macular degeneration (AMD) and cataracts, the two leading causes of visual impairment in people over age 50," said Johnson. "Cataract extractions are the most common surgical procedure in the country, at a cost of at least $3.4 billion per year to Medicare. AMD cannot be surgically treated and is the leading cause of blindness among the elderly."
"Because there is no cure for AMD, prevention is most important," she explained. "One risk factor that people can control is increasing the amount of lutein and zeaxanthin in their diet. That means including more green and yellow vegetables, as well as egg yolks. Although the amount of lutein in egg yolks is less than is found in vegetables, it is much more available to the body, that is, more easily and efficiently absorbed."
Recently Johnson's team identified obesity as another risk factor for AMD. Since lutein and zeaxanthin are fat-soluble nutrients, it is possible that increased adipose tissue (body fat) may affect the metabolism of these nutrients. Additionally, physiological changes that occur with obesity, such as increased inflammation and an altered lipoprotein profile, may play a role in increasing risk of eye disease.
The preponderance of evidence in favor of a protective role for lutein and zeaxanthin in eye health has led to a large government-sponsored clinical trial by the National Eye Institute.
"This multi-year study, in which half the participants receive lutein and zeaxanthin and half receive a dummy pill or placebo, and neither the subjects nor the investigators know who is getting what, will give us more definitive evidence about the effectiveness of these two compounds in delaying or preventing age-related eye disease," said Johnson.
Beyond their roles in eye health, lutein and zeaxanthin may also modulate some early processes involved in the development of cardiovascular disease and cancer.
Potential Reduction in Cardiovascular Disease Risk
Robert Nicolosi, PhD, of the University of Massachusetts at Lowell described basic research showing how lutein may reduce the development of fatty streaks -- one of the first steps in coronary artery disease. As an antioxidant, lutein may help prevent the oxidation of low-density lipoprotein cholesterol (LDL), the so-called "bad" cholesterol.
Once oxidized, LDL is taken up by macrophages (cells of the immune system) that occupy the subendothelial space of the blood vessel wall and eventually form foam cells and fatty streaks (early atherosclerosis), ultimately forming artery-narrowing plaques and setting the stage for heart attacks.
"Lutein has been shown to reduce the ability of these fat-engorged macrophages to adhere to arterial wall surfaces, as well as to reduce the levels of vascular cell adhesion molecules," said Nicolosi. "Both factors are believed to be important in decreasing fatty streaks, the early signs of plaque formation in coronary arteries."
Nicolosi also discussed epidemiological evidence from studies that compared either dietary intakes or blood levels of lutein/zeaxanthin in people with and without cardiovascular disease. The Los Angeles Atherosclerosis Study and the Atherosclerosis Risk in Communities (ARIC) Study both found an inverse association between blood levels of lutein and increased thickening of the carotid artery, a measure of heart attack risk. That is, people with the highest levels of lutein and zeaxanthin had the least thickening of their carotid arteries, and vice versa.
The ARIC study, as well as another epidemiological study in Washington County, Maryland, found that people newly diagnosed with heart attacks had lower blood levels of lutein than their matched controls (people similar to the heart attack cases in all health aspects, but free of heart disease).
In contrast, no such associations were seen in three large epidemiological studies conducted out of Harvard Medical School and the Harvard School of Public Health (Nurses' Health Study, Women's Health Study, Physicians' Health Study). However, another large Harvard study, the Health Professionals Follow-up Study, found an inverse relationship between lutein intake at the beginning of the study and subsequent incidence of stroke.
Some Hope for Lowered Cancer Risk
Data suggesting a possible role for lutein and zeaxanthin in reducing cancer risk were presented by Jeffrey Blumberg, PhD, a professor at the U.S. Department of Agriculture's Human Nutrition Research Center on Aging at Tufts University, Boston.
"There is a strong biological rationale from experiments in cell cultures and animal models supporting a protective role of lutein and zeaxanthin against the development of cancer, though results from human studies are mixed," said Blumberg.
"Nonetheless, several epidemiological studies reveal that people consuming high levels of these two carotenoids in their diets are at a reduced risk of cancers of the breast, colon, lung, prostate, and skin when compared to those consuming much less," he added. These observations are supported by studies showing a similar anti-cancer action in people with the highest concentrations of lutein and zeaxanthin in their blood.
While community-based studies cannot determine the specific cause and effect relationship between these two carotenoids and cancer, they are stimulating new investigations including clinical trials that may provide more definitive evidence about this possible health benefit of lutein and zeaxanthin.
Drs. Johnson, Blumberg and Nicolosi presented their talks at a session entitled, "Lutein: A Nutrient for the Ages," sponsored by the American Egg Board and the Egg Nutrition Center at the 58th annual scientific meeting of the Gerontological Society of America, a medical organization devoted to reducing diseases associated with aging.
SOURCE The Egg Nutrition Center
CONTACT: Kerri Reese of Aronow Communications, +1-212-265-5100, for The Egg Nutrition Center