Lutein (; from Latin luteus meaning "yellow") is a xanthophyll and one of 600 known naturally occurring carotenoids. In the human retina, lutein is absorbed from blood specifically into the macula lutea, although its precise role in the body is unknown. The principal natural stereoisomer of lutein is (3R,3R,6R)-beta,epsilon-carotene-3,3-diol. Lutein is a lipophilic molecule and is generally insoluble in water. The presence of the long chromophore of conjugated double bonds (polyene chain) provides the distinctive light-absorbing properties. The polyene chain is susceptible to oxidative degradation by light or heat and is chemically unstable in acids.

Lutein is present in plants as fatty-acid esters, with one or two fatty acids bound to the two hydroxyl groups. Lutein absorbs blue light and therefore appears yellow at low concentrations and orange-red at high concentrations.

Many songbirds (like golden oriole, evening grosbeak, yellow warbler, common yellowthroat and Javan green magpies, but not American goldfinch or yellow canaries) deposit lutein obtained from the diet into growing tissues to color their feathers.

Role in human eyes

Although lutein is concentrated in the macula – a small area of the retina responsible for three-color vision – the precise functional role of retinal lutein has not been determined. However, lutein and zeaxanthin had no overall effect on preventing AMD, but rather "the participants with low dietary intake of lutein and zeaxanthin at the start of the study, but who took an AREDS formulation with lutein and zeaxanthin during the study, were about 25 percent less likely to develop advanced AMD compared with participants with similar dietary intake who did not take lutein and zeaxanthin."

  • An updated 2023 Cochrane review of 26 studies from several countries, however, concluded that dietary supplements containing zeaxanthin and lutein alone have little effect when compared to placebo on the progression of AMD. In general, there remains insufficient evidence to assess the effectiveness of dietary or supplemental zeaxanthin or lutein in treatment or prevention of early AMD.

Cataract research

There is preliminary epidemiological evidence that increasing lutein and zeaxanthin intake lowers the risk of cataract development. Consumption of more than 2.4 mg of lutein/zeaxanthin daily from foods and supplements was significantly correlated with reduced incidence of nuclear lens opacities, as revealed from data collected during a 13- to 15-year period in one study.

Two meta-analyses confirm a correlation between high diet content or high serum concentrations of lutein and zeaxanthin and a decrease in the risk of cataract. There is only one published clinical intervention trial testing for an effect of lutein and zeaxanthin supplementation on cataracts. The AREDS2 trial enrolled subjects at risk for progression to advanced age-related macular degeneration. Overall, the group getting lutein (10 mg) and zeaxanthin (2 mg) were NOT less likely to progress to needing cataract surgery. The authors speculated that there may be a cataract prevention benefit for people with low dietary intake of lutein and zeaxanthin, but recommended more research.

In foods

Lutein is a natural part of a human diet found in orange-yellow fruits and flowers, and in leafy vegetables. No recommended dietary allowance currently exists for lutein. Some positive health effects have been seen at dietary intake levels of 6–10 mg/day. The only definitive side effect of excess lutein consumption is bronzing of the skin (carotenodermia). It is approved for use in the EU and Australia-New Zealand. In the United States, lutein may not be used as a food coloring for foods intended for human consumption, but can be added to animal feed and is allowed as a human dietary supplement often in combination with zeaxanthin.

Some foods contain relatively high amounts of lutein and zeaxanthin. In a ranking provided by the USDA FoodData Central database, the highest food levels of lutein and zeaxanthin (expressed together as micrograms per 100 grams of powder or fresh-frozen or raw weight) are found in paprika (18,900 micrograms per 100 g), frozen spinach, sweet potato leaves, dandelion greens, red cayenne pepper, and turnip greens (12,800 micrograms per 100 g).

Safety

In humans, the Observed Safe Level (OSL) for lutein, based on a non-government organization evaluation, is 20 mg/day. Although much higher levels have been tested without adverse effects and may also be safe, the data for intakes above the OSL are not sufficient for a confident conclusion of long-term safety.