While betacarotene, the precursor of vitamin A, may be the most familiar carotenoid, there are almost 600 others whose effects have yet to be extensively studied. Aside from lutein, these include alpha-carotene, lycopene, zeaxanthin, and beta-cryptoxanthin.
In the plant world, carotenoids like lutein help to give color to sweet potatoes, carrots, and other fruits and vegetables. In people, lutein and zeaxanthin make up most of the pigment in the center of the retina, where vision sensitivity is greatest.
While lutein is not considered an essential nutrient, studies suggest that it may play an important role in maintaining healthy vision and preventing eye diseases such as age-related macular degeneration (ARMD) and cataracts. Getting adequate amounts of this carotenoid may also decrease the risk of developing colon cancer and heart disease.
Lutein and other carotenoids are considered important because of their antioxidant properties. Antioxidants help to protect cells from damage caused by free radicals, the destructive fragments of oxygen produced as a byproduct during normal metabolic processes. As free radicals travel through the body, they cause damage to cells and genes by stealing electrons from other molecules—a process referred to as oxidation.
Test tube studies conducted by the Agricultural Research Service of the United States Department of Agriculture (USDA) suggest that lutein may be just as effective at combating free radicals as vitamin E, which is a potent antioxidant.
Concentrated mainly in the lens and retina of the eye, lutein may help to protect vision by neutralizing free radicals and by increasing the density of eye pigment. Lutein may also shield the eyes from the destructive effects of sunlight. In late 2001, a British study reported that risk of cortical cataract was lowest with high concentrations of lutein.
While not approved as a dietary supplement by the FDA, lutein is ubiquitous in foods. It may play an important role in maintaining vision and preventing such eye diseases as ARMD and cataracts, the two leading causes of vision loss in adults. The carotenoid may accomplish this by protecting eye tissue from free radical damage and shielding the eyes from potentially destructive sunlight.
Research also indicates that getting adequate amounts of lutein may decrease the risk of colon cancer and heart disease. Lutein may offer protection against the latter two diseases by acting as an antioxidant, since free radical damage is believed to contribute to the development of cardiovascular disease as well as certain cancers.
The results of an earlier study, published in the British Medical Journal in 1992, shed light on the possible link between lutein and cataracts. The objective of the study was to examine the relationship between cataracts and intake of carotenoids, vitamins C and E, and riboflavin.
Researchers studied the dietary habits via questionnaires of over 50,000 registered nurses aged 45 years and over for a period of eight years and found that those who reported consuming the most vitamin A and carotenoids were found to have a lower risk of developing cataracts.
Spinach, which is a rich source of lutein, appeared to offer the most protection against the disease. The researchers concluded that the carotenoids present in food may decrease the risk of developing severe cataracts.
Lutein may also help to prevent the development of colon cancer, according to a study published in the American Journal of Clinical Nutrition in 2000. This study examined the risk of colon cancer and dietary intake of lutein and other carotenoids such as alpha-carotene, beta-carotene, lycopene, zeaxanthin, and beta-cryptoxanthin.
The researchers examined the eating habits of over 4,000 people. Roughly half the participants were between the ages of 30 and 79 and already had colon cancer, while the remainder made up the cancer-free control group.
The results indicated that men and women who had consumed large amounts of lutein were less likely to develop the disease. Interestingly, lutein was the only carotenoid identified by the study that seemed to offer any protection.
The evidence regarding lutein and heart disease is indirect but intriguing. A study reported in 2001 found that carotid arteries in those with higher lutein levels were clearer than average.
A human study also provides some indirect evidence that higher levels of lutein and other carotenoids may play a role in preventing the development of cardiovascular disease.
The study, conducted by researchers from Cambridge University and published in 1996, examined blood levels of antioxidant vitamins and carotenoids in people from two regions of the world with very different rates of heart disease: Toulouse, France, and Belfast, Ireland.
The results showed that residents of Toulouse, who have a much lower rate of heart disease, had lutein levels about twice as high as those from Belfast, where the incidence of cardiovascular disease is much greater. The people from Toulouse also had higher blood levels of other carotenoids.
There is no RDA or Daily Value (DV) for lutein, and the optimum daily dosage has not been established with certainty. Therapeutic dosages range from 5–30 mg a day, though 6 mg daily is generally considered adequate.
Some authorities believe it is better for people to avoid lutein supplements altogether and increase their intake of foods known to contain lutein. Egg yolks are the richest source and also contain a large amount of zeaxanthin.
Other sources of lutein include corn, red seedless grapes, kiwi fruit, squash, and green vegetables such as zucchini, spinach, collard greens, kale, leaf lettuce, celery, peas, broccoli, and leeks. Oranges and orange juice, tomatoes, and carrots also prove good sources of lutein.
In 2001, researchers reported that concentrations of lutein are higher in the peels of fruits than in the pulp. The concentration of carotenoids increases as fruit ripens. Getting too much lutein through food and drink is not considered a significant risk because the nutrient is only present in relatively small amounts in plants and animals.
Lutein is not known to be harmful when taken in recommended dosages, though it is worth remembering that the long-term effects of taking lutein supplements are unknown. Due to lack of sufficient medical study, lutein should be used with caution in children, women who are pregnant or breast-feeding, and people with liver or kidney disease.
When taken in recommended dosages, lutein is not associated with any bothersome or significant side effects.
Lutein is not known to interact adversely with any drugs or dietary supplements.