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Supplement Spotlight: Lutein Keeps an Eye on Healthy Vision

By Yousry Naguib, Ph.D.

Vitamin Retailer magazine, May 2001

Lutein is one of the six prevalent carotenoids (including alpha-carotene, beta-carotene, beta-cryptoxanthin, lycopene, and zeaxanthin) present in human plasma. Lutein and zeaxanthin are oxygenated carotenoids, known as xanthophylls.

Lutein is a yellow substance, found in egg yolks, leafy green vegetables (spinach, broccoli, winter squash, alfalfa), and marigold flowers. It was first extracted from the corpus luteum, hence its name.

In humans, lutein and zeaxanthin are concentrated in the macula, a vital part of the retina in the eye, where images are focused. The retina is a thin layer of light-sensitive tissue that stretches across the back of the eyes where visual images are captured. The macula is a yellow spot at the center of the retina that allows us to see fine detail while reading, writing and driving. Lutein and zeaxanthin are strongly implicated in maintaining eye health. They filter out the blue light from the retina and prevent oxidative stress or free radical-induced damage in the eye's macula. Humans do not synthesize lutein and depend on dietary sources such as vegetables, eggs, and lutein supplements.

Bioavailability

The bioavailability of lutein in humans depends on the type of food, food matrix, other food ingredients such as fibers and fats, and on the type of processing.

To assess the bioavailability of lutein from vegetables, 22 healthy adults consumed a high-vegetable diet (490 grams/day), 22 consumed a low-diet (130 g/day), and 10 consumed a low-vegetable diet supplemented with beta- carotene (6 mg/day) and lutein (9 mg/day). Plasma concentrations of alpha- and beta-carotene, beta-cryptoxanthin, and lutein and zeaxanthin were significantly higher after the high-vegetable diet than after the low-vegetable diet. Plasma beta-carotene and lutein increased by 14 percent and 67 percent, respectively, after the high-vegetable diet, indicating that the bioavailability of lutein from vegetables is five times higher than that of beta-carotene (1).

Increasing the intake of vegetables and fruits also increased serum carotenoid levels in an at-risk-of-cancer population. A one year randomized, controlled-intervention study of men and women with a recent history of adenomas revealed that increasing vegetable and fruit intake to at least eight servings per day increased (by 11 to 54 percent) plasma carotenoids, alpha- and beta-carotene, beta-cryptoxanthin, lutein and zeaxanthin (2).

Another study involving 69 volunteers also showed that consumption of vegetable meals (broccoli, green peas, spinach; containing 1.7 to 24.6 mg. beta-carotene, 3.8 to 26 mg. lutein, 0.22 to 0.6 mg. folate, and 26 to 93 mg. vitamin Q for four days increased plasma concentrations of lutein and vitamin C significantly. In addition, broccoli and green peas were found to be better sources of lutein. Disruption of the spinach matrix increased the plasma concentrations of lutein and folate, indicating that the bioavailability of lutein from spinach can be improved by cooking (3).

A study on six healthy young women found that some dietary fibers such as pectin, guar, alginate, cellulose and wheat bran significantly reduced the bioavailability of lutein, lycopene and beta-carotene by 40 to 75% (4).

In a study described as the first to identify lutein esters (mainly lutein monopalmitate) in human serum blood, 18 non-smoking healthy volunteers were supplemented with lutein from a natural source (15 mg. per day as mixed lutein esters) for four months. On average, lutein concentration in serum increased five-fold after the first month of supplementation (5).

Herbst et al (1997) compared the bioavailability of lutein esters with that of crystalline lutein in humans. Healthy volunteers were given high dose of either lutein or lutein esters; their plasma were analyzed for lutein, and there was no statistically significant difference in plasma lutein between the two products (6).

The bioavailability of lutein also depends on the amount of fat in the diet. Volunteers were divided into four groups; each group received one of four different supplements: vitamin E (50 mg.), alpha- plus beta-carotene (8 mg.), lutein esters (8 mg, lutein), or placebo for two week-periods. The supplements were provided in a low- or high fat spread. Plasma concentrations of all supplements in the supplemented group were higher than in the placebo group. 'The plasma lutein level was higher when lutein esters were consumed with the high-fat spread (207 percent increase) than with the low-fat spread (88 percent increase). The study concluded that optimal uptake of vitamin E and alpha- and beta-carotene requires a limited amount of fat whereas the amount of fat required for optimal intestinal uptake Of lutein esters is higher (7).

Antioxidant Activity

The most likely physiological functions of lutein and zeaxanthin in the eye are protection against oxidative damage of the lipid matrix and protection against harmful UV radiation. These effects were evaluated in a test tube experiment, where both lutein and zeaxanthin were found to protect lipid membranes, prepared from egg yolk lecithin, against UV radiation and oxygen free radicals attack (8). In a similar experiment, lutein and zeaxanthin were found to be more effective antioxidants than alpha- and beta-carotene in inhibiting oxygen free radical mediated oxidation of liposomes from egg yolk (9).

Lutein and beta-carotene, carotenoids with and without provitamin-A activity, respectively, protected human liver cells against oxidant-induced damage, indicating that the antioxidant protective effect of carotenoids is independent of provitamin-A activity (10).

The plasma carotenoids lutein and beta-cryptoxanthin were shown in a two-week dietary intervention trial, involving 37 women who took 12 servings of fruits and vegetables daily and an additional 10 subjects who limited their consumption of fruits and vegetables to less than four servings per day, to correlate inversely with indices of oxidative DNA damage and lipid peroxidation (11).

The effect of an increased fruit and vegetable intake on the plasma levels of Iutein, lycopene, beta-carotene and vitamin E and susceptibility of lipoprotein (LDL) to oxidation was evaluated in smokers and non-smokers. Volunteers increased their intake of fruits and vegetables, to provide 30 mg. per day of-carotenoids, for two weeks. The carotenoid levels increased in smokers 23 percent and 11 percent in nonsmokers, and the resistance of LDL to oxidation increased by 14 percent in smokers and by 28 percent in non-smokers. The study suggested that the inhibitory effect of carotenoids on LDL oxidation might be beneficial in reducing the risk of atherosclerosis both in smokers and non-smokers (12).

Singlet oxygen has been implicated in biological systems and is capable of damaging proteins, lipids and DNA. A test tube experiment showed lutein to be as effective as vitamin E in quenching singlet oxygen (13).

Eye Health:

Age-Related Macular Degeneration:

Lutein and zeaxanthin are the only carotenoids that have been identified in the macula (a yellow spot in the retina that provides the best visual acuity) of the human eye, referred to as macular pigment. Lutein and zeaxanthin in the macula have been proposed to absorb short-wavelength light, which may otherwise cause photochemical damage, and to scavenge free radicals. Increasing intake of lutein and zeaxanthin has been shown to increase the density of the macular pigment and therefore may reduce the risk of age-related macular degeneration (ARMD). ARMD occurs when the cells of the macula become damaged and stop functioning; its symptoms include blurring of vision, colors appearing dim, and difficulty reading or performing work up close.

ARMD is the leading cause of blindness in people over 65 years. Oxidative stress has been implicated in ARMD, The retina is highly susceptible to oxidative stress because of its high consumption of oxygen, its high content of polyunsaturated fatty acids, and its exposure to light.

Observational studies have indicated that high intake of lutein and zeaxanthin from food, such as spinach and broccoli, is associated with a reduced risk of both age-related macular degeneration and cataracts.

The Eye Disease Case-Control Study, on 356 case subjects aged 55 to 80 years and 520 control-subjects, found that high plasma levels of lutein and zeaxanthin were associated with reduced risk of neovascular ARMD, which occurs when abnormal blood vessels behind the retina leak blood that damage the macula. The study suggested that increasing the consumption of foods rich in lutein and zeaxanthin, in particular dark green, leafy vegetables, might decrease tile risk of developing ARMD (14).

In a small study, lutein supplementation was found to increase the density of macular pigment five-fold in eight subjects who took 10 mg. lutein per day for 12 weeks. The study concluded that supplementation with lutein significantly increased the density of macular pigment (15).

When seven subjects consumed spinach and corn, which contained lutein and zeaxanthin, with their daily diets for 15 weeks, their serum concentrations of lutein and zeaxanthin increased significantly from baseline during dietary modification (16).

Another study on 19 subjects revealed positive, though weak, association between dietary intake of lutein and zeaxanthin, serum concentration of lutein and zeaxanthin, and macular density pigment (MP). The study suggested that low concentrations of macular pigment might be associated with an increased risk of ARMD (17).

A small 1999 intervention study on 14 male patients (average 70 years) demonstrated short-term improvement in visual function in one or both eyes with intake of five ounces sautéed spinach four to seven times per week or lutein supplement (18).

A 1997 study on 13 Subjects found that 80 percent of subjects given spinach (10.8 mg. lutein, 0.3 mg. zeaxanthin and 5 mg. beta carotene) and corn (0.3 mg. zeaxanthin and 0.4 mg. lutein) daily for 15 weeks had an increase in serum lutein (33 percent) and MP density (20 percent) as compared to those who were given only corn. The increased MP density remained elevated for several months after resuming regular diet (19).

Another 1997 study found that subjects consuming lutein esters, equivalent to 30 mg. free lutein per day for a period of 140 days, had a 20 to 40 percent increase in MP density (20).

An examination of 95 Subjects with respect to the iris color, MP density, and concentration of lutein and zeaxanthin in plasma revealed that the group with light (blue and gray) iris color had a significantly lower MP density than the group with brown or black iris. This is attributed to depletion of MP as a result of the tendency of light eyes to transmit more light than dark eyes, thus causing increased oxidative stress (21).

Retinitis pigmentosa:

Retinitis pigmentosa (RP) is an eye disease caused by over-activity of the pigmented retinal cells, leading to damage and occlusion of photoreceptors and blindness. A pilot Internet study examined the effects of lutein supplementation on visual acuity in some patients with retinal degeneration, including RP Sixteen patients (13 with RP, three with other retinal degeneration) completed a 26-week program of lutein supplementation (40 mg/day for 9 weeks, 20 mg/day thereafter). Participants self tested their visual acuity on their computer screens and their central visual field extent on a wall chart. After six weeks the study found short-term vision improvement after lutein supplementation in RP patients, especially in blue-eyed individuals (22).

Cataract:

Cataract is a white cloudy area in the lens of the eye that blocks some of the incoming light; its symptoms include blurred vision, sensitivity to light and glare, and halos around lights.

Dietary lutein and zeaxanthin also play a beneficial role in reducing the risk of age-related cataract caused by oxidation of lens proteins. In a prospective study of carotenoid intakes and risk of cataract extraction, the diet of 77,466 U.S. female nurses, aged 45-71 years, were followed for 12 years. Those with the highest intake of lutein and zeaxanthin had a 22 percent decreased risk of cataract extraction compared with those in the lowest quintile. Increasing frequency of intakes of spinach and kale, foods rich in lutein, was associated with a moderate decrease in the risk of cataract (23).

In a short-term follow-up study known as Beaver Dam Eye Study (Beaver Dam, WI), adults aged 43 to 84 years were examined for antioxidant intakes. Out of five carotenoids examined, only lutein was associated with cataracts — people with the highest lutein intake were half as likely to have cataracts as those with the lowest lutein intake (24).

A 1998 study found men who consumed the greatest amounts of the carotenoids lutein and zeaxanthin were 18 percent less likely to develop cataracts. The most protective foods were broccoli, kale and spinach (25).

A 1996 retrospective case-control study involving 207 cataract extraction patients and 706 controls showed that individuals consuming spinach were 40 percent less likely to have had cataract extraction compared to those who never ate spinach (26).

Other health benefits

High vegetable and fruit intakes have been associated with a decreased risk for various human cancers in epidemiological studies.

Dietary data from 1993 subjects with colon tumors and from 2410 control subjects revealed an inverse relationship between lutein and colon cancer in both men and women. The main dietary sources of lutein included spinach, broccoli, celery and greens (27).

A case-control study of diet and lung cancer in South Pacific populations showed an inverse association between lung cancer and lutein and vitamin E. Data from two prospective U.S. Studies (10 And 12 years follow-up periods) also found an inverse association between dietary lutein intake and lung cancer (28).

A study on serum carotenoid levels in breast cancer of women in India showed lutein and zeaxanthin levels to be significantly lower than healthy controls in postmenopausal, but not premenopausal, women (29).

A recent Italian study showed patients with type-2 diabetes have poor plasma status of vitamins A and E, and the carotenoids lutein, zeaxanthin, lycopene, beta-cryptoxanthin and alpha- and beta-carotene (30).

Different fatty acid esters of lutein, zeaxanthin and cryptoxanthin have been isolated from human skin. This finding and the antioxidant property of lutein lend support for its use in skin care (31).

In summary, several studies have established that higher intakes of the important antioxidants lutein and zeaxanthin increase plasma lutein concentration and macular pigment density, which are associated with factors that decrease age-related macular degeneration. Studies also support the beneficial role of lutein in reducing the incidence of cataracts and decreasing the risk of various cancers including colon, breast and lung cancers.

References
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