What is astaxanthin, and where does it come from?

Astaxanthin is a red pigment in the carotenoid family. In nature it is made by microalgae, above all Haematococcus pluvialis, and by some yeasts and bacteria; animals cannot make it, so salmon, shrimp, crab and krill take it in through their food. Commercial astaxanthin comes from three main places: Haematococcus algae, the yeast Phaffia rhodozyma, and chemical synthesis, which differ in how they are made and in their mix of molecular forms. On amounts, the European Food Safety Authority (EFSA) has set an acceptable daily intake (ADI) of 0.2 mg per kg of body weight, counting all sources together.

What is astaxanthin?

Astaxanthin belongs to the carotenoids, the family of yellow, orange and red pigments that also includes beta-carotene, lycopene and lutein (Shah et al. 2016). Within that family it is a xanthophyll, a carotenoid that contains oxygen as well as carbon and hydrogen.

The formula and molecular weight match PubChem, the chemical database of the US National Library of Medicine.

Where the name comes from

Nishida and colleagues (2023) recount that in the 1930s scientists isolated pigments from the shell and eggs of a lobster of the genus Astacus, and named the compound astaxanthin in 1938. The "asta" comes from Astacus, the lobster's genus name.

The structure of the molecule

Ambati and colleagues (2014) describe astaxanthin as two rings, one at each end, joined by a long chain of alternating double bonds (a polyene chain). Each ring carries a hydroxyl (-OH) group and a keto group, and the red colour comes from the run of linked double bonds in the middle of the molecule.

How is astaxanthin different from beta-carotene?

Both are carotenoids with 40 carbon atoms, but they differ in whether the molecule contains oxygen and in whether the body can turn them into vitamin A.

About vitamin A

The NIH Office of Dietary Supplements explains that the provitamin A carotenoids, namely beta-carotene, alpha-carotene and beta-cryptoxanthin, are converted into vitamin A in the intestine. Ambati and colleagues note that astaxanthin has no pro-vitamin A activity in humans, so it does not count as a source of vitamin A.

Where does astaxanthin come from in nature?

Made by algae, yeasts and bacteria

Nishida and colleagues (2023) note that, with the exception of animals, organisms that contain astaxanthin make it themselves, and that animals in general cannot make carotenoids. The best-known producer is the green microalga Haematococcus pluvialis. Ambati and colleagues (2014) report that it can build up astaxanthin to about 3.8% of its dry weight under stress, such as high salt, a lack of nitrogen, high temperature or strong light. Shah and colleagues (2016) describe the cells turning red at this stage and forming resting cysts.

Figures are from Table 1 of Ambati and colleagues (2014) and depend on the strain and growing conditions.

Passed up the food chain to seafood

Because animals cannot make it, the seafood that contains astaxanthin gets it from what it eats. Shah and colleagues (2016) list salmon, trout, red sea bream, shrimp, lobster and fish eggs among the seafood that contains it.

Why are shrimp, crab and salmon red or orange?

Part of the red-orange colour of salmon flesh and of shrimp and crab shells comes from the astaxanthin they take in with their food.

Colour in a lobster shell

Nishida and colleagues explain that in lobster shells astaxanthin is bound to proteins called crustacyanins, which appear blue to purple, whereas astaxanthin on its own absorbs light at around 470 nm. The colour of the shell therefore differs from the colour of astaxanthin by itself.

Farmed salmon get their colour from feed

Ambati and colleagues note that astaxanthin is used as a pigment in feed for salmon, trout and shrimp. In the United States, 21 CFR 73.35 allows astaxanthin in the feed of salmonid fish to give the flesh a pink to orange-red colour, at no more than 80 mg per kg of finished feed, and requires that fish raised on such feed declare the colour additive on the label. Nishida and colleagues also note that astaxanthin began with a modest role as a colouring agent in fish farming and poultry.

What types of astaxanthin are there?

Astaxanthin from different sources is the same basic molecule, but it comes in slightly different shapes (called stereoisomers) and in free or bound forms.

Different shapes of the same molecule

Ambati and colleagues explain that the (3S,3'S) and (3R,3'R) shapes are the most common in nature.

Shapes are from Ambati and colleagues (2014); the ester data for Haematococcus are from Shah and colleagues (2016).

Free or bound to fatty acids

Astaxanthin can be free, or attached at its hydroxyl groups to one or two fatty acids (called monoesters and diesters). Shah and colleagues report that mature red Haematococcus cells contain about 70% monoesters, 25% diesters and only 5% free astaxanthin.

How is synthetic astaxanthin different from astaxanthin from algae?

The main differences are how it is made and its mix of molecular shapes.

Shah and colleagues, writing in 2016, describe synthetic astaxanthin as made by a chemical reaction (a Wittig reaction). Ambati and colleagues state that commercial astaxanthin comes mainly from Phaffia yeast, Haematococcus algae and chemical synthesis.

Which foods contain astaxanthin?

In an ordinary diet, astaxanthin comes from seafood. Ambati and colleagues list salmon, trout, krill, shrimp and crayfish as natural sources, and note that shrimp, crab and salmon can be dietary sources.

Values are from Ambati and colleagues (2014); the per-100 g column is the same figure divided by ten. The review also notes that chum salmon contains little astaxanthin. Farmed fish get astaxanthin from their feed, so the amount depends on what they are fed.

Shrimp, crab and krill

The sources used here do not give figures per edible portion of shrimp, crab or krill. The one figure available is about 0.12% of dry weight for the cold-water shrimp Pandalus borealis (in the producer table above). Because it is a dry-weight figure, it cannot be compared directly with the salmon figures.

In Thai food

In Thai cooking, the foods that carry astaxanthin are the pink and red seafood: salmon, shrimp and prawns, crab, and fish roe.

Is there a safety limit for astaxanthin?

Astaxanthin is not a nutrient with a Thai Reference Daily Intake (Thai RDI), so there is no recommended daily amount in Thailand. The figure set by a food safety authority is EFSA's acceptable daily intake (ADI).

EFSA's ADI

EFSA set an ADI for astaxanthin of 0.2 mg per kg of body weight per day, counting all sources together: fish, shellfish and supplements. Because it is per kilogram of body weight, a lighter person reaches it at a smaller amount.

Where the figure comes from

EFSA explains that its Panel on Additives in Animal Feed (FEEDAP) set this value in 2019 from a two-year study in rats, dividing the lowest dose at which adverse effects were seen (40 mg per kg of body weight per day) by an uncertainty factor of 200. It replaced the earlier ADI of 0.034 mg per kg set in 2014, and in 2020 EFSA's Panel on Nutrition (NDA) considered that the same value also applies to astaxanthin from Haematococcus algae.

Children and teenagers reach it sooner

In its 2020 assessment, EFSA added a high intake from food (salmonid fish and crustaceans) to intake from supplements. It found that adolescents aged 14 to under 18 reached the ADI, while children under 14 exceeded it: by about 28% in those aged 10 to under 14, and by up to about 524% in infants aged 4 to 6 months. For children, amounts from all sources should be counted together.

Can I take astaxanthin while pregnant?

There is little information on astaxanthin in pregnant or breastfeeding women, so talk to your doctor before using a product that contains it.

Most of the data come from animals

The pregnancy data that Nishida and colleagues (2023) collected under reproductive and developmental toxicity come from studies in rats and rabbits. Results in animals cannot stand in directly for data in people. EFSA's 2020 assessment looked at different age groups but did not assess pregnant or breastfeeding women separately.

Seafood during pregnancy

Seafood that contains astaxanthin, such as salmon, shrimp and crab, is on the lower-mercury "Best Choices" list of the US FDA, which advises people who are pregnant or breastfeeding to eat 8 to 12 ounces (about 225 to 340 g) of a variety of seafood a week. The UK NHS advises pregnant women to have no more than 2 portions a week of oily fish such as salmon and trout, to avoid raw fish and shellfish, and to cook cold-smoked fish such as smoked salmon until steaming hot.

Who should be careful with astaxanthin?

Seafood allergies

Astaxanthin is found in seafood such as shrimp, crab, krill and salmon. The US FDA lists fish and crustacean shellfish among the major food allergens. People with a crustacean or fish allergy should talk to a doctor or pharmacist.

Children

Because the ADI is based on body weight, children reach it sooner than adults, as explained in the section on the safety limit.

When should I talk to a doctor or pharmacist?

If you are pregnant or breastfeeding, take a regular medicine, or have a crustacean or fish allergy, talk to a doctor or pharmacist before taking dietary supplements.

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