Astaxanthin is a carotenoid that gives salmon, shrimp, and flamingos their distinctive red-orange colour. First isolated from lobsters in 1938, it’s now one of the more popular antioxidant supplements on the market.

I should be honest from the start: while astaxanthin has genuinely impressive antioxidant properties in laboratory settings, the human clinical evidence is more modest than the marketing would suggest. That said, there are some areas where the research looks promising, and others where I wouldn’t bother spending money.

What is astaxanthin?

Astaxanthin belongs to the carotenoid family, making it a chemical cousin of beta-carotene and lycopene. Microalgae (particularly Haematococcus pluvialis) produce it as a protective response to stress conditions like intense light or nutrient scarcity. Marine animals that eat these algae accumulate astaxanthin in their tissues, which explains why wild salmon flesh is pink while farmed salmon often needs colouring added.

The molecular structure of astaxanthin includes two oxygenated ring groups, which gives it unusually strong antioxidant capacity. Laboratory studies suggest it may be 54 times more potent than beta-carotene and 65 times more potent than vitamin C at neutralising certain reactive oxygen species [1].

One interesting property: astaxanthin can cross the blood-brain barrier and span both sides of cell membranes simultaneously, theoretically offering more comprehensive protection than antioxidants that can only work in either water-soluble or fat-soluble compartments.

Since humans cannot synthesise astaxanthin, we depend entirely on dietary sources. Wild salmon provides roughly 3-4mg per 100g serving, while krill, shrimp, and crab offer smaller amounts.

Potential benefits of astaxanthin

Skin health and photoageing

This is probably astaxanthin’s strongest evidence area. A systematic review of six randomised controlled trials found that supplementation at 3-6mg daily improved skin moisture, reduced wrinkle depth, and offered some protection against UV-induced damage [2].

The mechanism makes theoretical sense: UV radiation generates reactive oxygen species in skin cells, and an antioxidant that can embed in cell membranes might help neutralise these before they cause structural damage. I wouldn’t expect miracles, but for people already using sunscreen and other protective measures, it might offer modest additional benefit.

Eye fatigue and circulation

Astaxanthin is structurally similar to lutein and zeaxanthin, two carotenoids that accumulate in eye tissue. A small study found that 12mg daily for four weeks increased blood flow to the choroid (the layer behind the retina) [3]. Another study in cataract patients found reduced oxidative stress in the aqueous humour.

The research here is preliminary, with small sample sizes. If you’re concerned about eye health, lutein has considerably more evidence behind it. But astaxanthin might be worth considering as part of a broader approach.

Cognitive function

Two trials in middle-aged and elderly subjects with mild memory complaints found that oral astaxanthin improved scores on cognitive tests, including reaction time and word recall [2]. The effect sizes were modest, and both studies were relatively small (60-96 participants).

I wouldn’t use astaxanthin hoping to prevent dementia or significantly boost cognitive performance. But for people already interested in the supplement for other reasons, the cognitive findings are at least not discouraging.

Type 2 diabetes markers

An 8-week trial in 44 people with type 2 diabetes found that astaxanthin increased adiponectin (a hormone associated with insulin sensitivity), reduced visceral fat, and lowered triglycerides and blood pressure [2].

Interesting? Somewhat. Conclusive? Not remotely. One small trial doesn’t establish a supplement as useful for diabetes management. If you have diabetes, focus on proven interventions first.

Exercise performance and muscle recovery

This is where I remain sceptical despite some positive findings. One cycling study found astaxanthin (4mg daily for 28 days) improved time trial performance by about 5% and increased power output [4]. A study in football players found reduced markers of muscle damage after intense training [5].

The problem: exercise performance studies are notoriously variable, and the effects here aren’t dramatic enough to rule out placebo or other confounding factors. Many supplements show promise in early exercise trials that doesn’t hold up with replication.

Mental fatigue

A 4-week trial of astaxanthin combined with sesamin found improved recovery from mental fatigue, particularly fatigue induced by prolonged screen use [6]. The combination makes interpretation tricky since we can’t know which ingredient did what.

Oxidative stress markers

A meta-analysis of nine trials found astaxanthin reduced malondialdehyde (an oxidative stress marker) and enhanced superoxide dismutase activity [7]. The catch: subgroup analysis showed effects only at doses of 20mg or higher, which is considerably more than most commercial supplements provide. At typical doses under 20mg, the antioxidant effects weren’t statistically significant.

Male fertility

One small trial (30 men over 3 months) found astaxanthin improved sperm motility and increased partners’ pregnancy rates compared to placebo [8]. Intriguing but far from definitive. Male fertility is influenced by dozens of factors, and single studies with small samples frequently fail to replicate.

Vocal cord protection

A study in 10 men found oral astaxanthin reduced markers of vocal cord damage after voice loading [9]. Interesting for professional voice users, but the study lacked a control group and had only 10 participants.

What the evidence doesn’t support

Carpal tunnel syndrome

A 9-week trial found astaxanthin added no benefit when combined with standard treatment (medication plus splints) [10]. If you have carpal tunnel, stick with proven approaches.

Blood lipids

A meta-analysis of seven trials found astaxanthin did not significantly improve cholesterol or triglyceride levels [11]. Despite in vitro studies suggesting it might regulate lipid metabolism, this doesn’t appear to translate to meaningful effects in humans.

Functional dyspepsia

A trial in 44 patients found no significant improvement in gastrointestinal symptoms at either 16mg or 40mg doses [12]. Some improvement in reflux symptoms occurred in the high-dose group with H. pylori infection, but overall the results were disappointing.

Kidney transplant recipients

A year-long study in 61 kidney transplant recipients found 12mg daily didn’t improve arterial stiffness, inflammation, or vascular function markers [13]. This is worth noting because cardiovascular disease is a major concern for this population, and astaxanthin didn’t help.

How to take astaxanthin

Astaxanthin is fat-soluble, so take it with food containing some fat for better absorption. Most studies use doses between 4-12mg daily, though the oxidative stress research suggests higher doses (20mg+) may be needed for measurable antioxidant effects.

There’s no established optimal dose, and individual responses likely vary. If you’re going to try it, I’d suggest starting with 4-6mg daily and taking it consistently for at least 4-8 weeks before evaluating whether it’s doing anything noticeable for you.

Side effects and safety

The safety profile appears reasonable. A study using 6g daily (far above typical supplement doses) for 8 weeks found no significant adverse effects or changes in blood chemistry [14].

Reported side effects are generally mild: some people experience increased bowel movements or stomach discomfort. The supplement can colour your faeces slightly (it’s a pigment, after all), which is harmless.

Who should avoid astaxanthin

Pregnant and breastfeeding women: No adequate safety data exists for these populations. Given the lack of clear benefit for most people anyway, there’s no good reason to take the risk.

People with bleeding disorders or on anticoagulants: Astaxanthin may have mild anticoagulant effects. Combined with warfarin or similar medications, this could theoretically increase bleeding risk. Relevant drugs include aspirin, clopidogrel, heparin, and other blood thinners.

People taking blood pressure medication: Some evidence suggests astaxanthin might lower blood pressure slightly. If you’re already on antihypertensives, this could cause excessive blood pressure drops.

People with diabetes on glucose-lowering medication: Given the possible blood sugar effects, there’s theoretical risk of hypoglycaemia if combined with diabetes medications.

People taking 5-alpha reductase inhibitors: Some research suggests astaxanthin might also inhibit this enzyme, which could lead to additive effects. These drugs include finasteride (used for hair loss and enlarged prostate) and dutasteride.

People with autoimmune conditions: Astaxanthin may stimulate immune function, which could theoretically worsen autoimmune disorders or interfere with immunosuppressive therapy.

People allergic to related compounds: If you’ve had allergic reactions to other carotenoids or to Haematococcus pluvialis, avoid astaxanthin.

People with calcium disorders: Some evidence suggests astaxanthin might lower serum calcium levels, which could be problematic for people with hypocalcaemia, osteoporosis, or parathyroid disorders.

Drug interactions

Astaxanthin may affect liver enzymes (cytochrome P450 system) that metabolise many medications. Potentially affected drugs include:

Benzodiazepines (diazepam)
Antidepressants (amitriptyline, fluoxetine)
Beta-blockers (propranolol)
Painkillers (morphine, ibuprofen, acetaminophen)
Statins (lovastatin)
Some antibiotics and antifungals (erythromycin, ketoconazole)
Steroids (corticosteroids)

If you take any medications regularly, check with your pharmacist before adding astaxanthin.

My honest assessment

Astaxanthin isn’t useless, but it’s not a miracle supplement either. The strongest evidence exists for skin health, where it might offer modest benefits for photoageing and UV protection. The eye health and cognitive research is preliminary but not unreasonable.

For most other claimed benefits, the evidence is either negative (blood lipids, carpal tunnel) or too preliminary to draw conclusions (exercise performance, diabetes markers, fertility).

If you want to try it for skin health, 4-6mg daily with a meal seems reasonable. For general antioxidant purposes, you might need higher doses (20mg+) based on the meta-analysis findings, which gets expensive quickly.

For eye health specifically, lutein has considerably more evidence. For general antioxidant support, vitamin E and CoQ10 might be more practical choices. If you’re interested in carotenoids from algae, spirulina offers a broader nutrient profile at lower cost.

Benefits and side effects of lutein - Another carotenoid with stronger eye health evidence
Benefits and side effects of spirulina - A natural source of astaxanthin
Benefits and side effects of vitamin E - A well-studied antioxidant

References

Higuera-Ciapara I, et al. Astaxanthin: a review of its chemistry and applications. Crit Rev Food Sci Nutr. 2006;46(2):185-96.
Davinelli S, et al. Astaxanthin in skin health, repair, and disease: A comprehensive review. Nutrients. 2018;10(4):522.
Yasunori N, et al. Effects of astaxanthin on accommodation, critical flicker fusion, and pattern visual evoked potential in visual display terminal workers. J Tradit Complement Med. 2012;2(4):265-274.
Earnest CP, et al. Effect of astaxanthin on cycling time trial performance. Int J Sports Med. 2011;32(11):882-8.
Djordjevic B, et al. Effect of astaxanthin supplementation on muscle damage and oxidative stress markers in elite young soccer players. J Sports Med Phys Fitness. 2012;52(4):382-92.
Imai A, et al. Effects of dietary supplementation of astaxanthin and sesamin on daily fatigue: a randomized, double-blind, placebo-controlled, two-way crossover study. Nutrients. 2018;10(3):281.
Xia W, et al. Effectiveness of astaxanthin as an antioxidant: A systematic review and meta-analysis. Oxid Med Cell Longev. 2019;2019:9580307.
Comhaire FH, et al. Combined conventional/antioxidant “Astaxanthin” treatment for male infertility: a double blind, randomized trial. Asian J Androl. 2005;7(3):257-62.
Kang SY, et al. Effects of astaxanthin on laryngeal injury induced by voice loading. Eur Arch Otorhinolaryngol. 2016;273(8):2227-33.
Nir Y, et al. A placebo-controlled, randomized, double-blind study evaluating the effectiveness of astaxanthin in carpal tunnel syndrome. Evid Based Complement Alternat Med. 2012;2012:185475.
Ursoniu S, et al. Lipid profile and glucose changes after supplementation with astaxanthin: a systematic review and meta-analysis of randomized controlled trials. Arch Med Sci. 2015;11(2):253-66.
Kupcinskas L, et al. Efficacy of the natural antioxidant astaxanthin in the treatment of functional dyspepsia in patients with or without Helicobacter pylori infection: A prospective, randomized, double blind, and placebo-controlled study. Phytomedicine. 2008;15(6-7):391-9.
Coombes JS, et al. Astaxanthin has no effect on arterial stiffness, oxidative stress, or inflammation in renal transplant recipients: a randomized controlled trial (the XANTHIN trial). Am J Clin Nutr. 2016;103(1):283-9.
Spiller GA, et al. Safety of an astaxanthin-rich Haematococcus pluvialis algal extract: a randomized clinical trial. J Med Food. 2003;6(1):51-6.