Lutein is a prevalent carotenoid in nature that plays an essential role in plant health by harvesting blue light and protecting the chloroplasts from oxidative damage. Humans and other primates are unique in that we are the only animals to selectively accumulate lutein in the retina of the eye and brain. Accumulation within the retina bestows us with a normal yellow macular pigmentation and protects the eye against blue light and oxidative damage. In what is surely the largest experimental trial to date to investigate age-related macular degeneration (AMD), supplementing lutein alongside other antioxidants reduced the progression of AMD to its advanced forms by 10% compared to the antioxidants alone.

Within the brain, lutein is the most prevalent carotenoid where it is believed to be neuroprotective through its role as an antioxidant. As outlined by a team of investigators from three Universities that seeks to understand the uptake and bio-localization of lutein in the brain and the association of lutein content with brain function,

The brain is especially vulnerable to free radical attack due to its high polyunsaturated fatty acid content and high metabolic activity. Lutein is differentially localized to membrane domains rich in polyunsaturated fatty acids including DHA, and therefore is well positioned to block oxidation of these vulnerable lipids [28]. Inhibition of DHA oxidation not only helps to maintain membrane structure and fluidity but also preserves DHA so it remains available for cleavage and conversion into anti-inflammatory molecules [29].

This protective role of lutein explains why there is a preferential accumulation and maintenance of lutein in the infant brain despite a low dietary intake from formula feeding, and why lutein concentrations of the developing infant brain correlate positively with lipid pathway metabolites indicative of cell-to-cell signaling and cell membrane integrity; energy pathway metabolites indicative of structural growth, myelination, and nervous conduction; brain osmolytes that regulate brain volume homeostasis; and amino acid neurotransmitters such as GABA that are responsible for neuronal activity.

In adults, retinal lutein concentrations are related to better cognitive functioning and supplementation with lutein has been shown to increase processing speed. Interestingly, retinal and brain lutein concentrations are related, which makes sense considering these are the two places we accumulate it. From a purely biological standpoint, ensuring adequate lutein intake appears to be essential for health, and the limited observational and experimental evidence to date supports this.

The best form of lutein

Lutein is found almost exclusively in plants and the best sources are dark green leafy vegetables such as spinach, kale, and broccoli. The only animal product to supply dietary lutein is the egg yolk, but its concentration of lutein is far less than that of plants and highly dependent on the type of feed provided to the bird. Generally speaking, a darker orange yolk will contain more lutein than a yellowish yolk.

Despite containing markedly less lutein, eggs do appear to be more bioavailable than plants. This was clearly demonstrated by researchers from Tufts University who had a small group of men consume similar test meals except for the source of lutein.

Test meals contained a sufficient amount of fat (55–60% of energy) to ensure optimal lutein absorption. In addition, the meals for the various treatments were designed to contain similar amounts of fat (18.8–20.4 g), carbohydrate (6.7–8.0 g), and protein (22.9–26.4 g).

Specifically, they ate a meal on day 1 of the intervention and were monitored from days 1-3, after which they consumed the same meal every day during days 4-10. This set-up allowed them to view how bioavailability of the lutein source difference acutely (change in serum levels from days 1-3) and semi-chronically (change after eating the meal daily until day 10). Each meal supplied the same amount of lutein (6 mg/day), and everyone completed all 4 treatments of lutein (lutein supplement, lutein ester supplement, spinach, and egg) in random order. As shown in figure 2, blood levels of lutein were significantly greater with the egg than with either supplement or the spinach.

The novelty of this study comes from the fact that each meal contained similarly generous amounts of fat, thus excluding the possibility that egg bioavailability is greater simply because of the fat content of the yolk. Clearly adding olive oil to your salad is not the same as eating an egg. This is supported by other research documenting improved lutein status among vegetarians who add 6 eggs per week into their diets.

Lutein from egg yolk is located in an easily digestible lipid matrix composed of cholesterol, triglycerides, and phospholipids. It is lutein’s polar structure that makes it fat soluble, and this property is also what allows it to integrate into the cell membranes of our brain and retina for protection. It stands to reason that this occurs in egg yolks as well, so as to protect the embryo from oxidative stress that may occur as it matures. Considering lutein’s role in our health and that no other animal products supply dietary lutein, why else would egg yolks contain lutein in concentrated amounts?

Perhaps it isn’t the fat per se, but the fact that lutein is bound to the phospholipid cell membranes. This concept was just recently tested not with eggs, but with a lutein supplement made by complexing lutein with phospholipids. A small group of older men and women were randomized to consume 10 mg lutein for 10 days either as a typical lutein ester or as a lipid-complex. The complex was the clear winner, with participants showing a 563% increase in serum lutein levels compared to an 88% increase for the conventional supplement.

Figure 3: Plasma lutein concentrations before and after 10 days supplementation with 10 mg/day of lutein. Lutein 1 = lutein ester. Lutein 2 = lutein lipid-complex. *Significantly different

The only issue with all this research is the fact that it equated the lutein doses. This is great in that it allows us to say without a doubt that lutein from eggs is more bioavailable than that from plants possibly because it is complexed with phospholipids. However, the fact that spinach contains anywhere from 5- to 25-fold more lutein per gram combined with the fact that egg yolks contain 14-fold more calories per gram cannot be overlooked. Egg-based lutein may be more bioavailable, but does this difference really matter in light of the increased amount you would get from plants? We don’t know, but it appears unlikely.

So eat your eggs and your dark leafy greens. Lutein is an essential carotenoid for health, as exemplified by our preferential accumulation of it in the brain and retina. It is most likely beneficial through acting as an antioxidant that protects the incredibly vulnerable polyunsaturated fatty acids of the brain from its high metabolic activity. The best sources of lutein by far are dark leafy green vegetables such as spinach, but egg yolks make a valuable contribution as well. Eggs may be more bioavailable (by far), but this difference is potentially outweighed by the greater quantities of lutein found in plants. So eat both.