Eggs for better Sight?
By Caroline Brider, B.Sc., Registered Dietitian

According to the most recent 2008 American Eye-Q ^© survey, only 29 percent of Americans are increasing nutrients in their diet to cope with the threat of vision loss or other eye problems. This survey also showed that 48 per cent of all Americans still believe carrots are the best food for eye health. The fact is that, while carrots are rich in the antioxidant pro-vitamin A beta-carotene, which is essential for night vision, other foods such as spinach and other dark leafy greens, which contain large amounts of lutein and zeaxanthin, are also emerging as some of the top nutrients for healthy vision. Eating a variety of coloured fruits and dark leafy vegetables, from 5-10 servings daily, will increase the levels of these antioxidants in the diet ¹.

Lutein and zeaxanthin are present in the macula segment of the retina and are believed to play a role in eye health, by improving macular pigment density. Some studies have shown that lutein alone or in combination with antioxidant nutrients appears to improve visual function in some patients with age-related macular degeneration. Research also shows that increasing the dietary intake of fruits and vegetables high in lutein and zeaxanthin is associated with an increase in macular pigment levels.The presence of these carotenoids in the macular pigment may absorb blue light before it can cause damage to the retina. There is no established daily recommended intake for lutein. Average daily intake is about 1-2 mg per day in American adults. Some research on the benefits of lutein supplementation on eye-related diseases suggests a dosage of 10-15 mg. Not everyone agrees on this, however, and some healthcare practitioners recommend lower levels, more in keeping with dietary intakes until the risks and benefits of these carotenoids are known2. Several dietary supplements containing lutein are available on the market today.

Lutein is found in dark green, leafy vegetables such as kale, broccoli, and collard greens, and at lower levels in corn and egg yolks. Corn, oranges, and papaya are sources of zeaxanthin. Interestingly, a regular egg supplies less lutein than spinach, but research has shown that the lutein found in the egg yolk is more bioavailable perhaps due to the lipid matrix of the yolk. Some eggs now on the market are enriched with lutein; making them a good source of lutein. Regular eggs provide approximately 150 micrograms of lutein. These specialty eggs now available in most grocery stores, are enriched with 1 mg (1000 micrograms) of lutein, six times that of a regular egg. Researchers have developed these eggs through a unique hen feed, consisting of marigold extract, extra corn and alfalfa, resulting in increased levels of lutein in these eggs. The lutein in eggs is found in the egg yolk, along with most key nutrients such as vitamin B12, choline, fat and cholesterol.

WHAT ABOUT THE CHOLESTEROL IN EGGS?

One recent study in healthy young men and women showed a correlation between egg consumption and cholesterol levels. When whole eggs were added to the participants diets, those whose serum cholesterol levels increased in response to egg intake, also had an increase in serum lutein levels (Clark et al.2006)3.This study demonstrated a relationship between changes in serum cholesterol and lutein concentrations in response to egg intake. Yet, other studies have shown different results. In a randomized, cross-over study by Goodrow et al., to determine the effect of egg supplementation on serum lipid levels and carotenoids levels in an older population ( mean age 79), participants were assigned to eat one regular egg per day for five weeks. While the serum levels of lutein and zeaxanthin had increased significantly, the levels of serum cholesterol did not differ amongst the study participants4. Yet an important question remained: would an increase in serum levels of lutein and zeaxanthin also increase the levels of those nutrients in the macula? In a study by Wenzel et al., 24 young women aged 24-59 were assigned to diets consisting of six carotenoid-rich eggs per week. The study found a statistically significant, linear increase in macular pigment optical density in the women who consumed the enriched eggs5. These studies suggest a wide variation in individual responsiveness to egg consumption. For most healthy individuals at low risk for heart disease, eggs are an excellent dietary choice. For those individuals who are on a restricted cholesterol diet, it is advised to limit egg consumption.

10 Food sources of Lutein and Zeaxanthin
The chart below shows levels of lutein and its accompanying molecule zeaxanthin naturally occurring in various fruits and vegetables*.

* U.S. Department of Agriculture, Agricultural Research Service,
USDA Nutrient Data Laboratory. 2005. USDA National Nutrient
Database for Standard Reference, Release 18. http://www.nal.usda.gov/fnic/foodcomp/search

References:
1 Source: American Optometric Association
2 MOZAFFARIEH M, Sacu S, WEDRICH A. “The role of the carotenoids, lutein and zeaxanthin, in protecting against age-related macular degeneration: A review based on controversial evidence”. J Nutr. 2003 Dec 11:2(1):20
3 CLARK RM, HERRON KL et al. “Hypo- and hyper-response to egg cholesterol predicts plasma lutein and {beta}-carotene concentrations in men and women”. J. Nutr.2006;136:601-7.
4 GOODROW EF, HANDELMAN G, NICOLOSI RJ, et al. “Consumption of one egg per day increases serum lutein and zeaxanthin in older adults without altering serum lipid and lipoprotein cholesterol concentrations”. J.Nutr 2006;136:2519-2524
5 WENZEL AJ, NICOLOSI RJ, HANDELMAN GJ, et al. « A 12-week egg intervention increases serum zeaxanthin and macular pigment optical density in women”. J.Nutr 2006;136:2568-2573