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The "super antioxidant" astaxanthin (C40H52O4) is structurally similar to beta-carotene (C40H56). However, while beta-carotene has only 11 double bonds, astaxanthin has 13 conjugated double bonds. These and the two oxo groups (double bonded oxygen to carbon atom) give astaxanthin its antioxidative effect. Comparative studies have shown that astaxanthin has a much stronger antioxidant effect than other compounds. For example, astaxanthin is 6000 times stronger than vitamin C, 770 times stronger than coenzyme Q10, 100 times stronger than vitamin E, 55 times stronger than synthetic astaxanthin, 5 times stronger than beta-carotene, 3 times stronger than lutein and 2 times stronger than lycopene. In terms of its antioxidant activity, astaxanthin has other advantages. Its chemical structure enables it to intercept different types of free radicals. At the same time, astaxanthin is considered a "gentle" antioxidant because, compared to other antioxidants, the molecule does not itself become a highly reactive compound after the absorption of a free radical (3)(4). Astaxanthin is considered safe and has been certified by the United States Food and Drug Administration (FDA) as GRAS (generally recognized as safe) status (5). After ingestion in the form of supplements or carotenoid-rich food, astaxanthin enters the intestinal cells together with dietary fats through passive diffusion. Similar to other carotenoids, astaxanthin is transported in chylomicrons and via the lymph into the blood. This is also how the transport to the respective target tissue takes place (6). The bioavailability of astaxanthin depends on numerous factors. For example, the combination with dietary fats increases bioavailability 2.4-fold, so simultaneous intake with a meal should be considered (7). In addition, the combination of Astaxanthin with dietary fats in supplements increases its bioavailability 2 to 4-fold (8). Another advantage is obtained by extracting astaxanthin from Haematococcus pluvialis. As this form of astaxanthin is esterified, it is more stable and is better absorbed by the body. Unesterified astaxanthin can oxidise particularly easily (9)(10)(11). Finally, smoking increases the breakdown of astaxanthin and can greatly reduce bioavailability (12).
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Oxidative balance describes the relationship between the production of reactive oxygen species (ROS) and the activity of antioxidant protective systems. If this system is in balance, oxidative damage can be minimized and body cells optimally protected. Often, chronic stress, environmental pollution or even exercise can lead to an imbalance: oxidative stress is increased, which can ultimately result in cell damage, various diseases or premature aging. Astaxanthin is able to restore this balance. A classic target group for astaxanthin are smokers. The high levels of ROS in cigarette smoke cause increased oxidative damage to lipid, protein and DNA structures. In addition, smokers experience both reduced activity of antioxidative enzymes and generally lower concentrations of antioxidants. An intervention using astaxanthin demonstrated a significant reduction of biomarkers for oxidative stress after only three weeks. At the same time, the concentrations in antioxidative protective systems increased (12). Astaxanthin is similarly effective in overweight or obese persons. In one study, treatement with Astaxanthin resulted in reduction of Malondialdehyde by 35 % and isoprostanes by 65 %; both are important biomarkers for oxidative stress. The positive effects on superoxide dismutases - a class of enzymes that metabolize reactive superoxide anions to hydrogen peroxide - were even stronger. Here the activity could be increased almost 3-fold. The total antioxidative capacity (TAS) also increased by more than 120 % (13).
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The human ageing process is associated with mitochondrial damage, increased oxidative stress and less active cell protection systems. This is considered to be one of the main causes for the development of various diseases in old age. Characteristic age-related symptoms are damage to the skin, increased oxidation of blood lipids and retinal damage. Astaxanthin can successfully counteract these aging processes.
Preservation of the skin
As a barrier, the human skin is permanently exposed to various environmental influences: UV radiation, environmental toxins and various mechanical and chemical influences. It is therefore obvious that the skin is particularly stressed by reactive oxygen species. The barrier function of the skin is additionally reduced by the progressive aging process, as the skin, which steadily becomes thinner by nature, is particularly sensitive to UV radiation. The direct consequences are increased pigmentation, reduced elasticity and premature aging of the skin. However, the antioxidant astaxanthin can also be used for this indication. It is not only able to counteract hyperpigmentation and wrinkling but also increases the skin elasticity and moisture. It can also reduce UV-induced skin damage. All in all, astaxanthin supports the preservation of the appearance of youthful skin - even in old age. Two studies from Japan are particularly worth mentioning in which the astaxanthin intervention reduced wrinkles around the eye area and the size of age spots in the cheek area, improved skin texture and increased skin hydration and elasticity (14). A study published in June 2018 on the UV protection of astaxanthin investigated whether supplementation with 4 mg astaxanthin/day increases the skin's minimum erythema dose (MED). The minimum erythema dose (also called erythema threshold dose) is a measure of the tolerance of human skin to solar radiation and indicates the amount of UV radiation the skin tolerates before the first signs of redness appear. After completion of astaxanthin intake, MED was significantly increased; this effect did not occur in the placebo group. At the same time, the UV-irradiated skin areas of the astaxanthin group showed less moisture loss. The subjective perception of improvement in rough skin and overall skin texture was also significantly more positive in the intervention group (15).
Protection from lipid peroxidation
Astaxanthin-mediated protection from lipid peroxidation was investigated in a study examining the effects of astaxanthin supplementation on the lipid profile and antioxidant parameters (TBARS, TAS and 8-isoprostane) of postmenopausal women. TBARS (thiobarbituric acid reactive substances) are biomarkers for the extent of lipid peroxidation; TAS (total antioxidant status) and 8-isoprostane are markers for oxidative stress. Astaxanthin has been shown to increase HDL cholesterol and decrease triglyceride levels. At the same time it reduced the extent of lipid peroxidation by lowering TBARS. TAS levels also increased, reflecting an improvement in the functioning of antioxidant protective systems. However, there was no effect on 8-isoprostane, LDL and total cholesterol (16).
Protection against age-related eye damage and changes in visual behaviour
Presbyopia, also known as the ageing eye condition, is not a disease, but describes the progressive age-related loss of the eye's ability to adapt to near vision. A sharp vision in the near range without suitable correction is then no longer possible. If this loss of function is left untreated, asthenopic complaints - such as stiff neck and shoulders, eye pain and headaches - occur, which significantly impair the quality of life. A 2009 study investigated whether and how astaxanthin affects the side effects of incipient presbyopia. The results were unequivocal: the convergence miosis improved significantly in the majority of subjects. This describes the unilateral or bilateral pupil constriction following a visual stimulus. Symptoms such as overstrained eyes, blurred vision or shoulder and neck tension also improved (17). There is also initial evidence of the benefit of astaxanthin in Computer Vision Syndrome (CVS). CVS, also known as digital eye strain, is the combination of eye and vision problems caused by regular use of computers and other digital devices such as smartphones. Typical symptoms range from headaches and sleep disturbances to exhaustion, reddened eyes, dizziness or blurred vision. Astaxanthin is able to counteract the effects of the everyday digital life. For example, the carotenoid reduced the refocusing time of the eye by 46 % and improved accommodation - the ability of the eye to actively adapt visual acuity to different distances - by 27 % (18)(19).
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Cardiovascular disease, and in particular coronary heart disease (CHD), accounts for almost half of all deaths in the European Union and is the leading cause of mortality. Chronic inflammatory processes and increased oxidative stress are significantly involved in the pathophysiology of cardiovascular disease and atherosclerosis. Nonetheless, the study results on antioxidant micronutrients for primary and secondary prevention of atherosclerosis are the subject of controversy. Since drugs - such as statins, calcium antagonists or diuretics - are associated with a wide variety of side effects, they suffer from low compliance among patients. This makes the development of new prevention and therapy methods all the more important: The cardioprotective effects of astaxanthin, with its unique chemical properties, have been studied for some time. The following sections discuss individual aspects and reflect the current consensus in the literature (20).
Protection against LDL oxidation
The oxidative modification of LDL or the change in size and density of LDL particles is seen as the underlying cause for the initiation of the atherosclerotic process. Whether astaxanthin can protect LDL particles from oxidation is not yet clearly established. In some animal studies, the antioxidant astaxanthin reduced LDL by 30%, other studies did not show significant results. In human studies conducted between 2000 and 2011, the results tend to suggest that astaxanthin protects against lipid and LDL peroxidation (20).
Reduction of blood pressure
It is estimated that by 2025 more than 1.56 billion people will be affected by high blood pressure. This makes it all the more important to adopt effective measures to counteract existing hypertension. The hypotensive effects of astaxanthin in animal models are clear and show significant reductions in systolic (up to 28 mmHg) and diastolic (up to 23 mmHg) blood pressure. Results from human studies are still too few to make a reliable statement (20).
Reduction of blood glucose and diabetes
The most recent meta-analysis of the antidiabetic effects of astaxanthin indicates that the carotenoid has at least a minor blood glucose-lowering effect. Potential mechanisms discussed are improvement of insulin sensitivity, reduction of oxidative stress and inflammation, and support of endothelial function (20)(21). Further evidence for the cardioprotective potential of astaxanthin is provided by an RCT published in 2018: An eight week intervention with 8 mg astaxanthin/day was performed in diabetics. Particularly noteworthy were the significant astaxanthin-induced reduction in total fat mass and the reduction in triglyceride levels. At the same time, blood pressure and VLDL levels decreased compared to a placebo. Positive effects on fructosamine and adiponectin levels were also observed. Fructosamine provides a longer-term picture of blood glucose levels and is also known as "blood sugar memory". Adiponectin is a peptide hormone which is produced in fat cells. It regulates both the feeling of hunger and food intake and modulates the effect of insulin. Overweight people often have reduced adiponectin levels, which weakens insulin efficiency (22).
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