How do astaxanthin, beta-carotene and lutein differ?

Astaxanthin, beta-carotene and lutein are all carotenoids: pigments built on the same 40-carbon skeleton, with a long chain of linked double bonds in the middle and a ring at each end. They differ in what sits on those end rings, in whether the body can turn them into vitamin A, and in which foods contain them. Beta-carotene (C40H56) contains only carbon and hydrogen, and the body converts it into vitamin A. Lutein (C40H56O2) and astaxanthin (C40H52O4) contain oxygen, and the body does not turn them into vitamin A. Beta-carotene and lutein come mainly from vegetables and fruit; astaxanthin comes from seafood.

In short:

• Beta-carotene: no oxygen in the molecule; becomes vitamin A in the body; orange and yellow vegetables and leafy greens
• Lutein: a hydroxyl group on each end ring; not vitamin A; leafy greens, sweet corn and egg yolk
• Astaxanthin: a hydroxyl and a keto group on each end ring; not vitamin A; salmon, shrimp, crab and fish roe
• Daily amount: only vitamin A has a Thai RDI (800 µg RAE); lutein and astaxanthin have none

This article compares the three by structure and by the foods that contain them. For astaxanthin in seafood, see Which foods contain astaxanthin, and how much?

What do astaxanthin, beta-carotene and lutein have in common?

All three are carotenoids

A 2016 review by Shah and colleagues describes astaxanthin as a red carotenoid from the same family as lycopene, lutein and beta-carotene. The NIH Office of Dietary Supplements (ODS) describes the provitamin A carotenoids, including beta-carotene, as plant pigments.

Two groups: carotenes and xanthophylls

Carotenoids that contain only carbon and hydrogen, such as beta-carotene and lycopene, are called carotenes. Those that also contain oxygen are called xanthophylls. The 2014 review by Ambati and colleagues explains that astaxanthin is a xanthophyll because it contains oxygen atoms as well as carbon and hydrogen. Lutein and zeaxanthin are xanthophylls for the same reason.

How do their structures differ?

The three share the same 40-carbon skeleton. The difference is on the two end rings.

Beta-carotene: carbon and hydrogen only

PubChem, the chemistry database of the US National Library of Medicine, gives beta-carotene the formula C40H56. Its rings carry no oxygen.

Lutein and zeaxanthin: one hydroxyl group on each ring

PubChem gives lutein the formula C40H56O2, with a hydroxyl group on each end ring. Zeaxanthin has the same formula. The two differ only in the position of one double bond in one of the rings, as their chemical names in PubChem show.

Astaxanthin: a hydroxyl and a keto group on each ring

Shah and colleagues give astaxanthin's chemical name as 3,3'-dihydroxy-beta-carotene-4,4'-dione. Put simply, it is the beta-carotene skeleton with a hydroxyl group and a keto group added to each ring. Ambati and colleagues give its formula as C40H52O4 and explain that its red colour comes from the linked double bonds at the centre of the molecule.

Which of them can the body turn into vitamin A?

Only beta-carotene, of these three.

Provitamin A and non-provitamin A carotenoids

The ODS says the body converts the provitamin A carotenoids (beta-carotene, alpha-carotene and beta-cryptoxanthin) into vitamin A in the intestine. It says other carotenoids in food, such as lycopene, lutein and zeaxanthin, are not converted into vitamin A and are called non-provitamin A carotenoids. Ambati and colleagues note that astaxanthin has no pro-vitamin A activity in humans.

How beta-carotene is counted

The ODS explains that vitamin A is counted in retinol activity equivalents (RAE). By the US measure, 1 µg RAE equals 1 µg of retinol or 12 µg of beta-carotene from food. Because beta-carotene becomes vitamin A, it counts towards vitamin A intake. The Thai Reference Daily Intake (Thai RDI) for vitamin A is 800 µg RAE a day.

Which foods are high in beta-carotene and lutein?

Beta-carotene and lutein often come from the same vegetables, but in different proportions. Orange vegetables are richest in beta-carotene, and dark leafy greens in lutein.

Amounts per 100 g

The figures below come from the US Department of Agriculture's FoodData Central database (SR Legacy). FoodData Central lists lutein and zeaxanthin as one combined value. The last column compares the vitamin A value of the food with the Thai RDI of 800 µg RAE.

The vitamin A value of egg comes mainly from retinol, the form of vitamin A found in animal foods, rather than from beta-carotene. "Raw" means uncooked; for mango and papaya it means the ripe fruit, uncooked. Thai varieties may give somewhat different amounts.

Amounts in a typical serving

The serving weights are the US portion sizes listed in FoodData Central; the amounts are the per-100 g values above scaled to that weight.

Astaxanthin is in seafood instead

FoodData Central does not list astaxanthin for these vegetables. Ambati and colleagues name shrimp, crab and salmon as dietary sources, and report about 2.6 to 3.8 mg per 100 g of flesh in wild sockeye salmon. The amounts in seafood and the effect of cooking are covered in Which foods contain astaxanthin, and how much?

Where do commercial lutein and astaxanthin come from?

Lutein from marigold flowers

A 2023 review from China states that marigold flowers are a main source of commercial lutein, and that the microalga Haematococcus pluvialis and the yeast Phaffia rhodozyma are suitable species for commercial astaxanthin production. How natural and synthetic astaxanthin are made is explained in How are natural and synthetic astaxanthin made?

Egg yolk colour depends on the hen's feed

A 2019 study from the University of Wisconsin–Madison notes that the feed additives used to improve egg yolk colour are typically made from marigold flowers. In its trial with 40 laying hens, yolks from hens fed white maize without any added pigment had less lutein than yolks from hens fed carrot leaves or marigold. The lutein in an egg therefore depends on what the hen eats.

What do Thai studies show about these pigments?

Indigenous vegetables from southern Thailand

A 2015 study from the Institute of Nutrition, Mahidol University, analysed 15 indigenous vegetables and fruits collected in southern Thailand. Indian lettuce (Lactuca indica) had the most beta-carotene, 3,575.54 µg per 100 g, and water dropwort (Oenanthe javanica, phak chi lom) had the most lutein, 7,439.11 µg per 100 g. Young cashew leaves and mon-pu (Glochidion perakense) were also rich in both. The study covered one region and the samples collected there.

Gac fruit

A 2011 study from Mahasarakham University analysed the parts of Thai gac fruit (fak khao). The aril (the layer around the seeds) had the highest lycopene and beta-carotene, while the yellow peel had the most lutein. The same fruit therefore carries different carotenoids in different parts.

How much lutein Thai adults eat

A 2022 study from Kasetsart University and the Institute of Nutrition, Mahidol University, asked 120 adults aged 40 to 72 in Bangkok and nearby areas about their usual diet. Their average lutein and zeaxanthin intake was 3.03 mg a day. The study lists ten foods that contributed most, led by Chinese bitter gourd at 0.94 mg a day. The authors note that intake was estimated with a semi-quantitative food frequency questionnaire, which relies on self-report.

How much is too much?

Beta-carotene

The ODS says the US Food and Nutrition Board has not set an upper intake level for beta-carotene and other provitamin A carotenoids, but advises against beta-carotene supplements for the general population. With long-term excess beta-carotene, the skin can turn yellow-orange; the ODS describes this as harmless and reversible when the high intake stops. For preformed vitamin A (retinol), the US upper limit for adults is 3,000 µg a day.

Astaxanthin and lutein

Astaxanthin and lutein have no Thai RDI. For astaxanthin, the European Food Safety Authority has set an acceptable daily intake of 0.2 mg per kg of body weight, counting all sources, as explained in What is astaxanthin, and where does it come from?

When should I talk to a doctor or pharmacist?

If you are pregnant or breastfeeding, or take a regular medicine, talk to a doctor or pharmacist before taking dietary supplements, including those with vitamin A or beta-carotene.

Dietary supplements are not intended to prevent, treat or cure any disease.