Lutein
1. Identity, Chemical Nature, and Natural Sources
Lutein (pronounced /ˈljuːtiɪn, -tiːn/; from Latin luteus, meaning "yellow") is a xanthophyll and one of approximately 600 known naturally occurring carotenoids. It is a plant pigment, a xanthophyll, and a dihydroxy carotenoid. Its IUPAC name is β,ε-carotene-3,3′-diol, and because humans are not capable of synthesizing carotenoids in vivo, the lutein found in human tissues is normally of dietary origin. Structurally, carotenoids are tetraterpenoids with a 40-carbon skeleton made up of eight isoprene units. Lutein belongs to the oxygenated carotenoid (xanthophyll) subclass and is classified as a non-provitamin A carotenoid — it cannot be converted into vitamin A in the body.
Lutein is isomeric with zeaxanthin, differing only in the placement of one double bond. Within the body, lutein and zeaxanthin can be interconverted through an intermediate called meso-zeaxanthin. Lutein has a sequence of ten conjugated carbon-carbon double bonds. It is a red/orange crystalloid substance that is insoluble in water and has a melting point of 190°C (374°F).
Natural Sources
Lutein is synthesized only by plants and is found in high quantities in green leafy vegetables such as spinach, kale, and yellow carrots. Additional sources include alfalfa, wheat grass, barley grass, broccoli, green beans, green peas, lima beans, cabbage, collards, mustard greens, turnip greens, marigold flower petals, yellow fruits and vegetables such as carrots, peaches, mango, papaya, squash, oranges, as well as egg yolks, chicken skin, and chicken fat. In green plants, xanthophylls act to modulate light energy and serve as non-photochemical quenching agents to deal with triplet chlorophyll, an excited form of chlorophyll that is overproduced at high light levels during photosynthesis.
Marigold (Tagetes spp.) flower petals are the most vital commercial sources of carotenoids, especially lutein esters, for the production of natural lutein used in food, feed, and pharmaceutical industries. Commercially, lutein is usually extracted from the petals of the Aztec marigold (Tagetes erecta). Traditionally, marigold flowers and saponified oleoresin have been used in poultry feed to impart yellow/orange color in egg yolk. The carotenoid composition of marigold oleoresin typically contains approximately 70% trans-lutein, 20% cis-lutein, 7% zeaxanthin, and small amounts of epoxides and other minor compounds.
On average, the combined daily dietary intake of lutein plus zeaxanthin ranges around 2 mg for the United States population, but for some populations, such as South Pacific islanders, it may be as high as 26 mg per day due to unusually high intake of fruits and vegetables rich in these carotenoids.
2. Traditional and Historical Use
The isolation and identification of lutein as a discrete chemical entity is a relatively recent scientific achievement, but foods rich in lutein have been consumed and valued by many cultures for thousands of years in the context of broad dietary practices and herbal medicine traditions.
Lutein has traditionally been used since the 1950s for the treatment of eye diseases and for its purported protective effect on visual function. In 1996, the incorporation of lutein into dietary substances was accepted at approximately 6 to 7 mg/day, with marigold-sourced lutein used as a food additive and colorant.
Most studies conducted up to the 1990s investigated the efficacy of total carotenoid content, whereas more recent studies focus specifically on lutein. Researchers in the 1970s noted lutein's accumulation in the retina, leading to its description as an "eye vitamin" in popular media, though it is technically not a vitamin.
The primary commercial and folk-medicinal use of Tagetes erecta (African or Aztec marigold) flowers predates scientific characterization. Considering the high content of lutein, the industry extensively uses marigold flowers for natural lutein production for functional food, feed, cosmetics, and pharmaceuticals. In addition to lutein extraction, marigold flowers are extensively used in poultry feed to improve egg yolk pigmentation.
Available data have been obtained from both observational studies investigating lutein intake from food and a smaller number of intervention trials assessing the efficacy of lutein supplementation. Because lutein was not identified as a specific compound until the modern era, classical and traditional medicine systems did not prescribe "lutein" per se but used lutein-containing plants for eye-related complaints and general nutrition.
3. Key Constituents and Mechanisms of Action
Chemical Structure and Properties
Carotenoids are tetraterpenoid molecules with a 40-carbon skeleton and can be divided into two classes: carotenes (purely unsaturated hydrocarbons) and xanthophylls (oxygenated carotenoids). Lutein is a member of the xanthophyll class. The molecule contains a sequence of ten conjugated carbon-carbon double bonds, a structural feature that underlies its capacity to absorb visible light (particularly in the 400–500 nm blue-light range) and to quench reactive oxygen species.
Accumulation in Human Tissues
Lutein is well absorbed and systemically localized to the liver, lung, and retina, where it can cross the blood-retina barrier and accumulate in the macular pigment. Lutein is found in human tissues including serum (0.1–1.23 μM), liver (0.1–3.0 μM), kidney (0.037–2.1 μM), and lung (0.1–2.3 μM). By far the highest concentration is found in the human retina (0.1–1 mM), providing evidence for active uptake or storage.
Although lutein is not the most abundant carotenoid in the diet, it is the carotenoid found at the highest concentration in human brain tissue. Lutein and zeaxanthin account for 66 to 77% of the total carotenoid concentration in human brain tissue.
Antioxidant Mechanisms
Lutein and zeaxanthin can filter blue light to prevent the formation of reactive oxygen species, especially singlet oxygen, in the retina, and can further reduce oxidation by directly quenching singlet oxygen and related free radicals in the retina. The ability to remove harmful singlet oxygen is proportional to the number of conjugated double bonds in the carotenoid molecule.
Macular pigment acts as an optical filter for blue light and provides antioxidant protection to the human retina by inhibiting the peroxidation of long-chain polyunsaturated fatty acids. Macular xanthophylls are mainly localized in retinal membranes around Henle's fibers and in the membranes of photoreceptor outer segments. Their localization in the prereceptor layer is attributed to a role as a filter against harmful short-wave blue light. Their presence in receptor membranes, which are rich in polyunsaturated fatty acids and prone to peroxidation, is associated with their antioxidant function.
Anti-inflammatory Mechanisms
Among the most important pharmacological effects described in the literature are inhibition of pro-inflammatory responses produced by interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), and IL-1β, as well as protection against cardiac complications, neurodegeneration, and anti-cancer effects.
Bioavailability and Absorption
Depending on solubilization in the digestive system, the bioavailability of lutein is approximately 10–15%, which is considered poor. Free and esterified forms of lutein are both bioavailable, but supplements containing free lutein may increase the serum/plasma lutein response more than supplements containing lutein esters. Only free lutein is absorbed, so esterified lutein requires an additional ester-hydrolysis step in the small intestine. Lutein and zeaxanthin can be absorbed intact or undergo oxidative cleavage prior to absorption from the intestinal lumen and are transported in the blood by lipoproteins, associated with LDL and HDL.
Daily supplementation with lutein for 15 days significantly increases serum lutein in normolipemic adults to levels associated with reduced risk of age-related eye disease, regardless of the chemical form of lutein supplied.
4. Scientific Evidence by Area of Use
4.1 Age-Related Macular Degeneration (AMD)
The strongest and most consistent body of clinical evidence for lutein concerns its role in AMD. The role of lutein and zeaxanthin in human eye health is well established from epidemiological, clinical, and interventional studies. They constitute the main pigments found in the yellow spot of the human retina, protect the macula from damage by blue light, improve visual acuity, and scavenge harmful reactive oxygen species. They have also been linked with reduced risk of AMD and cataracts.
AREDS2 Trial (Primary Clinical Evidence): AREDS2 investigators enrolled 4,203 participants, ages 50–85, at 82 clinical sites across the United States. The trial included only people with intermediate AMD in both eyes or intermediate AMD in one eye and advanced AMD in the other eye. In the AREDS2 trial, adding omega-3 fatty acids or lutein + zeaxanthin to the original AREDS formula had no additional overall effect on the risk of advanced AMD. However, AREDS2 participants who took antioxidants minus beta-carotene but with lutein + zeaxanthin had an incremental increase in benefit compared to those who took the AREDS formula.
The AREDS2 study group found that individuals low in dietary lutein and zeaxanthin at baseline were about 25% less likely to develop advanced AMD compared to participants with similar dietary intake who did not take lutein and zeaxanthin supplements. Formulations containing lutein and zeaxanthin and no beta-carotene showed an 18% reduction in developing advanced AMD compared to participants who took the AREDS2 formula with beta-carotene and no lutein or zeaxanthin.
In analyses restricted to eyes with bilateral large drusen at baseline, direct comparison of lutein/zeaxanthin versus beta-carotene showed hazard ratios of 0.76 (95% CI, 0.61–0.96; P=0.02) for progression to late AMD and 0.65 (95% CI, 0.49–0.85; P=0.002) for neovascular AMD. The totality of evidence on beneficial and adverse effects from AREDS2 and other studies suggests that lutein/zeaxanthin could be more appropriate than beta-carotene in the AREDS-type supplements.
Long-term follow-up (AREDS2 Report 28): Long-term follow-up results of the AREDS2 cohort suggest that lutein/zeaxanthin was an appropriate replacement for beta-carotene in AREDS2 supplements. Beta-carotene usage nearly doubled the risk of lung cancer, whereas there was no statistically significant increased risk with lutein/zeaxanthin. When compared with beta-carotene, lutein/zeaxanthin had a potential beneficial association with late AMD progression.
Meta-analysis of macular pigment optical density (MPOD): A meta-analysis evaluated the effects of lutein supplementation on MPOD in randomized controlled trials involving patients with AMD. Nine RCTs involving 920 eyes (855 with AMD) were included. Meta-analysis of studies reporting lutein concentrations in serum showed that lutein concentration was significantly higher in the treatment group than in the placebo group (MD 1.10; 95% CI 0.54 to 1.67). Meta-analysis of studies reporting contrast sensitivity showed that lutein supplementation was associated with higher contrast sensitivity at spatial frequencies of 3, 6, 12, and 18 cycles per degree (MD 0.26; 95% CI 0.22 to 0.30).
A systematic review and meta-analysis found significant increases in macular pigment optical density (MPOD; WMD=0.069; 95% CI: 0.040–0.098, P=0.000) among AMD patients taking lutein supplementation. Subgroup analysis suggested that the dose and duration of supplementation could significantly influence MPOD. A larger increase in MPOD was observed with higher dosage (20 mg/day) and longer treatment duration (>6 months).
Overall evidence strength for AMD: The evidence is among the strongest available for any dietary supplement in a specific disease setting. Multiple large RCTs, meta-analyses, and a landmark multicenter trial (AREDS2) support a clinically meaningful effect, particularly in individuals with intermediate-to-advanced AMD who have low dietary intake of these carotenoids.
4.2 Age-Related Cataracts
The body of evidence from different study types suggests that lutein and zeaxanthin are likely to be two dietary components that protect against nuclear cataract, but if this is the case, the level needed to protect against lens opacity development is likely to be in the range of 0.5 to 1 mg/day, which is below the average intake in American adults (1.7 mg/day). Ensuring that all subgroups of the population achieve this minimal intake might substantially lower the visual burden of cataracts and the risks and expense associated with cataract surgery on a population level.
The AREDS2 trial also specifically assessed the effect of lutein/zeaxanthin on cataract. The AREDS and AREDS2 studies demonstrated that supplements including vitamins C and E, beta-carotene, and zinc may reduce the progression to advanced AMD in some patients by 25% in five years, representing one of the few nutritional supplements known to have beneficial effects in any eye disease. However, the cataract-specific findings from AREDS2 were less conclusive than the AMD findings.
Overall evidence strength for cataracts: Epidemiological and some observational evidence suggests a protective association. However, direct interventional evidence from RCTs is less robust than for AMD, and this area warrants further clinical investigation.
4.3 Diabetic Retinopathy
In comparing diabetic subjects, those with retinopathy had lower MPOD than subjects without, and MPOD levels correlated with glycosylated hemoglobin levels. One study demonstrated that daily supplementation of nonproliferative diabetic subjects with 6 mg lutein and 0.5 mg zeaxanthin increased MPOD, improved visual acuity (VA) and contrast sensitivity (CS), and increased foveal thickness compared to controls.
Evidence supporting the role of macular pigments in the prevention and treatment of diabetic retinopathy is currently limited, but animal models and early human supplementation trials suggest there is a role for lutein and zeaxanthin in reducing oxidative damage and possibly preventing disease progression. Despite limitations in individual studies, the increasing body of scientific evidence suggests that lutein may be beneficial in preventing retinopathy and its progression.
Overall evidence strength for diabetic retinopathy: Preliminary and limited. The available human trials are small in sample size, and large confirmatory RCTs are lacking.
4.4 Cognitive Function and Brain Health
Lutein and zeaxanthin are fat-soluble dietary carotenoids with high concentrations in human brain tissue. Although lutein is not the major carotenoid in the diet, it is the carotenoid of the highest concentration in human brain tissue, and lutein and zeaxanthin account for 66 to 77% of the total carotenoid concentration in human brain tissue. Lutein and zeaxanthin have been identified in the hippocampus, cerebellum, and frontal, occipital, and temporal cortices.
For example, 12 months of supplementation with 10 mg of lutein and 2 mg of zeaxanthin were associated with improvements in complex attention and cognitive flexibility in community-dwelling older adults, buffered cognitive decline on a verbal learning task in older adults, and increased spatial memory in young, healthy adults.
A systematic review of observational studies and RCTs in healthy individuals found that in six of the seven included clinical trials, increasing intake of lutein and zeaxanthin resulted in increased MPOD and improvements in cognitive function, though the types of tests and domains tested varied across studies.
However, in a large 5-year study on older-age adults with intermediate or advanced age-related macular degeneration, lutein and zeaxanthin supplementation did not change cognitive function as measured by standardized assessments.
Overall evidence strength for cognitive function: Preliminary and mixed. Several smaller RCTs and observational studies are encouraging, but results are heterogeneous across populations and cognitive domains tested. Larger, confirmatory trials are needed before firm conclusions can be drawn.
4.5 Cardiovascular Health
An ancillary Cardiovascular Outcomes Study of AREDS2 evaluated the effect of macular xanthophylls (lutein 10 mg/day + zeaxanthin 2 mg/day) versus omega-3 fatty acids versus a combination versus placebo on cardiovascular outcomes in 4,203 AREDS patients over a median of 4.8 years. Only patients with a negative baseline history for hypertension, cardiovascular disease, or hypercholesterolemia showed significant protective effects from either group of supplements.
Lutein has demonstrated remarkable potential benefits for neurodegenerative diseases, cardiovascular health, and liver protection. However, this evidence is largely from epidemiological associations and mechanistic studies rather than from large, powered cardiovascular outcomes trials.
Overall evidence strength for cardiovascular health: Weak-to-moderate. Epidemiological associations exist, and mechanistic data support a plausible role for lutein's antioxidant and anti-inflammatory properties in cardiovascular protection, but large dedicated clinical trials are lacking.
4.6 Cancer
With regard to the involvement of lutein in cancer development and progression, the findings are still uncertain. Lutein belongs to the carotenoid family of xanthophylls, which have reported antioxidant, anti-inflammatory, and anticancer properties.
An epidemiological study conducted in the Pacific Islands indicated that people with high intakes of a combination of β-carotene, α-carotene, and lutein had the lowest risk of lung cancer. Epidemiological associations have been noted for lutein intake and reduced rates of breast, colon, lung, and other cancers, but causal clinical evidence in humans is not established.
Overall evidence strength for cancer: Weak and preliminary. Evidence is primarily epidemiological and based on in vitro or animal models. Robust human interventional evidence is lacking, and specific claims cannot be made.
4.7 Skin Health
Lutein and zeaxanthin are found in the skin and subcutaneous tissue and protect against UV radiation and reactive oxygen species. Higher concentrations of fasting plasma carotenoids and enhanced skin yellowing after lutein consumption indicate its presence in various regions of the human body, including the skin, breast, brain, and cervix.
Overall evidence strength for skin health: Preliminary. Mechanistic and observational data support a plausible role, but large clinical trials specific to skin outcomes are lacking.
4.8 Dry Eye Disease
One randomized controlled trial investigated the effects of combined supplementation with lutein, zeaxanthin, and elderberries in 110 voluntary participants. Participants took 6 mg of lutein and 1 mg of zeaxanthin, along with 100 mg elderberry extract once daily for 20 days. Ocular health was assessed using the Ocular Surface Disease Index (OSDI). Results showed that combined supplementation significantly (p < 0.05) reduced OSDI scores in the intervention group from 38.15 ± 11.14 to 18.26 ± 5.57, reflecting a 52.2% reduction.
Overall evidence strength for dry eye disease: Early and limited. A small number of trials show promise but more research is needed, particularly to isolate the specific contribution of lutein from other co-administered ingredients.
5. Body Systems and Health Areas Associated with Lutein
- Ocular/Visual System: Most extensively studied. Lutein concentrates in the macular region of the retina and is directly implicated in AMD, cataract, and general visual function. Many basic and clinical studies have reported lutein's anti-oxidative and anti-inflammatory properties in the eye, suggesting its beneficial effects on protection and alleviation of ocular diseases such as age-related macular degeneration, diabetic retinopathy, retinopathy of prematurity, myopia, and cataract.
- Neurological/Brain: The lutein level in the macula was found to be significantly correlated with its concentration in matched brain tissue. Associations with cognitive function and neuroprotection are under active investigation.
- Cardiovascular System: Epidemiological associations suggest a protective role; the antioxidant and anti-inflammatory mechanisms of lutein are proposed as the underlying basis.
- Skin and Integumentary System: Lutein and zeaxanthin are found in the skin and subcutaneous tissue and protect against UV and reactive oxygen species.
- Immune System: Anti-inflammatory actions through inhibition of cytokines such as IL-6, TNF-α, and IL-1β are documented in cellular and animal studies.
- Gastrointestinal and Hepatic: Lutein is localized to the liver, lung, and retina. Research into liver and intestinal protective effects is preliminary.
6. Dosage Forms and Dosages Reported in Studies
Commercial Forms
Lutein and zeaxanthin preparations are derived from the oleoresin of marigold (Tagetes erecta) petals obtained by hexane extraction and purified by saponification and crystallization. The medicinal ingredient must comply with the specifications outlined in FAO/WHO 2022 or USP-NF 2022 monographs (Lutein, Lutein Preparation).
Lutein is available commercially in the following forms:
- Free (non-esterified) lutein: Used widely in dietary supplements. Supplements containing free lutein may increase the serum/plasma lutein response more than supplements containing lutein esters.
- Lutein esters (esterified lutein): In marigold flower petals, lutein is acylated with saturated fatty acids such as stearic, palmitic, myristic, and lauric acid moieties. Upon ingestion, esterified lutein partially undergoes hydrolysis in the presence of pancreatic secretions in the small intestine to regenerate free lutein, which is then absorbed.
- Beadlet formulations: Formulations such as starch-matrix beadlets (e.g., FloraGLO® Lutein) and cross-linked alginate-matrix beadlets have been evaluated in double-blind, cross-over studies for plasma kinetics.
- Marigold oleoresin extract: Used in food coloring and feed.
Dosages Used in Clinical Studies
- AREDS2 enrolled 4,203 participants at risk for AMD. The lutein + zeaxanthin arm used 10 mg/day lutein + 2 mg/day zeaxanthin over a median of approximately 5 years.
- In a prospective Japanese study of 16 subjects aged 26–57, subjects took a supplement containing 20 mg/day of lutein, 4 mg/day of zeaxanthin, and other antioxidants for 16 weeks.
- In a cross-over study assessing bioavailability from free versus esterified lutein, 24 healthy subjects consumed 6 mg lutein/day from marigold extract for two months.
- One RCT on dry eye disease used 6 mg/day of lutein plus 1 mg/day zeaxanthin for 20 days.
- One supplementation trial in nonproliferative diabetic subjects used 6 mg lutein and 0.5 mg zeaxanthin daily.
- Meta-analysis data suggest that a higher dose (20 mg/day) and longer treatment duration (>6 months) yields greater increases in MPOD in AMD patients.
- Case-control studies suggest a combined dose of 6 mg of lutein and zeaxanthin per day for reducing the risk of AMD.
- The recommended daily intake of lutein is approximately 10.0 mg; average dietary intakes in adults are 1–2 mg/day.
7. Safety Considerations and Interactions
General Safety Profile
Lutein is categorized as Generally Recognized as Safe (GRAS), posing minimal side effects upon long-term consumption. Long-term supplementation of dietary lutein has not been shown to have any adverse effects in humans. Studies found higher doses of lutein (30 mg and 40 mg/kg body weight) to be safe. Lutein did not show any safety concerns in rats and monkeys in preclinical studies.
Reported Adverse Effects
The AREDS2 trial reported no adverse effects — with the exception of some skin yellowing — from lutein and zeaxanthin supplementation (10 mg and 2 mg/day, respectively) over an average of 5 years in patients with intermediate AMD.
In a case study, bilateral "foveal sparkles" (crystalline deposits) were reported in an older woman who took a 20 mg/day lutein supplement for 8 years, along with exceptionally high dietary lutein intake. Seven months after discontinuing the lutein supplement but continuing her dietary habits, the crystals resolved in the right eye but not in the left eye. This case is considered rare and isolated.
Bioavailability Considerations
Many host-specific metabolic factors influence lutein bioavailability, such as single-nucleotide polymorphisms (SNPs) in proteins important for intestinal absorption, transport, and metabolism of lutein. The dissolution of the lutein formulation has an important influence on its bioavailability. Lutein is a lipid-soluble compound, and dietary fat intake at the time of supplementation is expected to enhance absorption, consistent with known properties of lipophilic carotenoids.
Beta-Carotene Interaction
In the AREDS2 trial, participants were randomly assigned to lutein/zeaxanthin and/or ω-3 fatty acids or placebo versus beta-carotene. Beta-carotene usage nearly doubled the risk of lung cancer, whereas there was no statistically significant increased risk with lutein/zeaxanthin. This finding is clinically significant in that high-dose beta-carotene (but not lutein) appears to carry a meaningful lung cancer risk in smokers and former smokers, supporting the preference for lutein/zeaxanthin over beta-carotene in supplementation formulations.
Allergen Considerations
Since most commercial lutein supplements are derived from marigold (Tagetes erecta) flowers, individuals with known allergies to plants in the Asteraceae/Compositae family should exercise caution.
Population-Specific Considerations
Although safety data are available for lutein, future studies should evaluate chronic consumption of high lutein-containing supplements in specific populations. No clinically established drug–drug interactions with lutein have been confirmed in the literature, though lutein — as a lipophilic compound transported via lipoproteins — may theoretically interact with other lipid-soluble compounds competing for intestinal absorption or lipoprotein transport.
References
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