Lutein

Dietary sources of lutein include:

• Egg yolks at 143+/-28μg per yolk,^[1] 292+/-117μg,^[2] 197.14+/-131.4μg or 598.92+/-131.7μg (different batches of eggs),^[3]

• Spinach at 18mg/100g (after cooking)^[4]

• Corn at 267μg/100g (after cooking)^[4]

Lutein appears to be highest in spinach, and also appreciably high in eggs (which are known to be the best absorbed food form of lutein) although the concentration in eggs appears to be highly variable

In regards to zeaxanthin, it has similar distribution in food at:

• Egg yolks at 94+/-18μg per yolk,^[1] 213+/-85μg^[2] 364.98+/-177.8μg and 133.35+/-56.70μg,^[3]

• Spinach at 500μg/100g (after cooking)^[4]

• Corn at 200μg/100g (after cooking)^[4]

A diet considered high in fruits and vegetables is thought to confer 2.3mg of lutein and 300μg of zeaxanthin daily,^[4] and when measuring total carotenoids it appears that the ratio of lutein to zeaxanthin appears to be around 1.44:1 and 1.69:1 (approximately three parts lutein to two parts zeaxanthin).^[3]

Carotenoids in general (β-carotene, lycopene, lutein) tend to have better absorption when paired with a lipid matrix^[5] and being bound to plant sources tends to reduce absorption (similar to other fat soluble phytonutrients like Vitamin K) although this impairment is alleviated somewhat with heat treatment of the plant.^[6][5] Due to this, eggs are better sources of lutein than spinach^[7] and spinach appears to be equivalent to dietary supplements even when said supplements are ingested with a mixed meal.^[7]

There do not appear to be differences in absorption between corn oil and beef tallow as fat sources in the diet, as despite the differences noted between groups in this study^[2] they were due to baseline differences and both groups normalized to around 400-420nM lutein.

Lutein appears to be best absorbed when ingested with fatty acids, and when it is not from a plant source that has failed to undergo heat treatment; among food products, this means that egg consumption appears to be the best dietary predictor of lutein levels in serum

Consumption of one egg daily (143μg lutein and 94μg zeaxanthin) in older adults for five weeks has been noted to raise steady state plasma lutein (26%; from around 160nM to 210nM) and zeaxanthin (38%; from around 40nM to 58nM)^[1] whereas an average of 1.3 eggs daily for around this time frame has elsewhere been noted to increase plasma lutein (28-50%; up to 400-420nM) and zeaxanthin (114-142%; up to 105-116nM) relative to the time period before egg consumption, although these eggs had a higher carotenoid content.^[2] Increasing consumption of eggs to 2-4 daily (243+/-24μg lutein and 230+/-31μg zeaxanthin per yolk) appears to also increase serum lutein 16-24% (137-142nM to 164-176nM) and zeaxanthin 36-82% (33nM to 45-60nM).^[8]

Consumption of enriched eggs (1.9mg lutein) has been noted to increase plasma concentrations of lutein 88% relative to baseline after eight weeks (240nM to 450nM).^[9]

When looking at egg consumption, at little as one egg (yolk) a day appears to increase plasma lutein by around 20-30% over baseline levels; it seems to be a pretty steady increase, while zeaxanthin seems more dose-dependent

When looking at supplementation of lutein, 10.23mg lutein ester (5.5mg lutein) and 6mg lutein in free form appear to increase plasma lutein concentraitons in a time dependent manner after a single dose (20-29%) and increasing up until 10 days of supplementation (82%) with no significant differences between groups;^[7] however, both groups underperformed 6mg of lutein via egg products (58% acutely, 323% after 10 days) even when all lutein doses were taken with a mixed meal and performed equally to spinach.^[7] 

Lutein esters appear to raise plasma lutein itself, as no esters are detected.^[7]

Supplements of lutein appears to increase plasma lutein, and the degree it increases plasma lutein is comparable to spinach but lesser than eggs

When in serum, lutein appears to associate with triglyceride rich lipoproteins;^[7] the degree of lutein enrichment is variable and is measured in the range of 0.6-16.8nM/g protein (average of 4.8-6.2nM/g) following supplementation of 6mg and 1.8–51.0nM/g protein (average of 11.1+/-5.2nM/g) following the same dose via eggs which are better absorbed.^[7]

This variability has been noted previously with lutein and other dietary carotenoids^[4][10][11] and may be due to variations in baseline triglycerides, although increases in serum lutein still exist when triglycerides are corrected for.^[7] This correlation with triglycerides has been noted before with β-carotene, where higher triglyceride responses to a meal were met with higher carotenoid exposure^[12] and higher triglyceride content in chylomicrons was met with higher carotenoid exposure.^[10]

Distribution of lutein, similar to other carotenoids, is due to being carried around in the body via triglyceride rich lipoproteins. There appears to be variability in how enriched these lipoproteins are following consumption of lutein

One study has noted that 13 weeks of a washout period was insufficient to reduce circulating lutein concentrations to baseline levels^[1] and others have utilized a 6 month washout with success;^[7] this highly suggests a storage of lutein in the body after supplementation.

It is not consensus, as one study using eggs as an intervention noted that four weeks was sufficient to reduce lutein and zeaxanthin to baseline levels.^[8]

Lutein appears to be stored well in the body, and can remain at levels higher than baseline even 13 weeks after cessation of supplementation

Lutein, zeaxanthin, and a lutein isomers known as meso-zeaxanthin are collectivly referred to as "macular pigment" due to them being dietary pigments that collect in the macula of the eye^[13] where they act as a high energy blue light filter (460nm wavelength) and protect underlying retinal cells.^[14]

Lutein and structurally related carotenoids are known to accumulate in the eye where they can buffer light and protect underlying retinal cells from oxidative stress

Aged-related macular degeneration (ARMD^[15]) is an age-related degenerative eye disorder which appears to affect up to 5% of persons above the age of 65, and of the two variants of AMD ('dry' and 'wet' AMD) dry AMD appears to be responsive to dietary manipulation and interventions.^[16][17] Lutein, as well as zeaxanthin, are investigated for their benefits due to bioaccumulating in retinal tissue when consumed in the diet and higher intakes of dietary lutein being associated with less risk for ARMD^[18][19] and higher retinal lutein concentrations being associated with less risk.^[20]

AMRD is a degenerative eye disorder affecting mostly the elderly, and while there are two possible variants of AMRD one of them is known to be responsive to dietary components and lutein (or more specifically, macular pigment) is thought to be protective against this form of AMRD

When looking at macular concentrations of lutein following supplementation of lutein, it appears that most (but not all) persons experience an increase in macular lutein concentrations (19+/-11% relative to baseline) that is slightly lesser than the increases in serum (33+/-22%) and if a serum increase dose not occur then a macular increase does not occur.^[4] Zeaxanthin can also increase in the eyes following supplementation (25%) to a level lesser than that seen in blood (70%).^[4]

Egg consumption has also been noted to raise plasma and macular carotenoid levels, although there has been one study that failed to find an increase in macular lutein (despite a serum increase) with one egg a day (zeaxanthin was increased)^[3] and 2-4 eggs a day has shown protection associated with total macular pigment being increased;^[8] this protective effect has occurred even in the presence of statin drugs in one study.^[8]

Dietary and supplemental lutein and zeaxanthin can increase total macular pigment levels, and associated with this increased macular pigment concentration comes protective effects in aged persons