Carotenoids

1. What This Class of Substances Is

Carotenoids are fat-soluble tetraterpenes with conjugated double bonds that function as pigments in plants, algae, and bacteria. They comprise over 600 naturally occurring compounds, including astaxanthin, lutein, zeaxanthin, lycopene, and beta-carotene. Chemically, they can be divided into oxygen-free carotenes and oxygen-containing xanthophylls. Their structure enables light absorption in the visible spectrum and antioxidant properties through radical-scavenging mechanisms. Natural sources include intensely coloured fruits, vegetables, and microalgae such as Haematococcus pluvialis.

Measuring carotenoids in humans is challenging, as their bioavailability depends on factors such as fat intake, matrix effects, and individual gut microbiota. While plasma levels and tissue concentrations can be assessed in the laboratory, their correlation with clinical effects often remains unclear. Additionally, metabolism and distribution vary between organs, complicating the interpretation of biomarkers. Controlled studies are resource-intensive, as placebo controls are difficult to implement with coloured substances.

2. Which Materials Are Included

All substances in the database for which this mechanism of action is described—ordered by the extent of human testing. The numbers represent studies per type of investigation.

3. How Robust the Evidence Is

Astaxanthin stands out with 40 controlled human studies, followed by omega-3 fatty acids (17) and anthocyanins (6). These compounds demonstrate reproducible effects on oxidative stress parameters, skin ageing, and inflammatory markers. Other carotenoids, such as lutein or lycopene, have primarily been investigated in laboratory and animal studies, with few human findings. Humic acid complexes, quercetin, or resveratrol show scarcely any controlled human data, despite promising laboratory results.

This class of compounds combines antioxidant and inflammation-modulating effects, based on their ability to donate electrons and stabilise membranes. While astaxanthin and omega-3 fatty acids demonstrate synergistic effects in studies, systematic investigations are lacking for other combinations (e.g., carotenoids with polyphenols). Translating laboratory findings to humans often remains speculative, as dosage, bioavailability, and long-term effects are unresolved.

4. Key Human Studies

• 1 Safety of an astaxanthin-rich Haematococcus pluvialis algal extract: a randomised clinical trial (2003) — Astaxanthin
• 2 Antioxidant effect of astaxanthin on phospholipid peroxidation in human erythrocytes (2011) — Astaxanthin
• 3 The protective role of astaxanthin for UV-induced skin deterioration in healthy people—a randomised, double-blind, placebo-controlled trial (2018) — Astaxanthin
• 4 Krill oil improved osteoarthritic knee pain in adults with mild to moderate knee osteoarthritis: a 6-month multicentre, randomised, double-blind, placebo-controlled trial (2022) — Omega-3 fatty acids
• 5 A multicentre, randomised, double-blinded, placebo-controlled clinical trial to evaluate the efficacy and safety of a krill oil, astaxanthin, and oral hyaluronic acid combination (2023) — Omega-3 fatty acids
• 6 Characteristics of participants who benefit most from personalised nutrition: findings from the pan-European Food4Me randomised controlled trial (2020) — Omega-3 fatty acids
• 7 A randomised, double-blind, placebo-controlled study of oral antioxidant supplement therapy in patients with dry eye syndrome (2016) — Anthocyanins (berries)
• 8 Antioxidative capacity of a dietary supplement on retinal haemodynamic function in a human lipopolysaccharide (LPS) model (2014) — Anthocyanins (berries)
• 9 Effects of different combinations of phytochemical-rich fruits and vegetables on chronic disease risk markers and gene expression changes: insights from a 2024 study — Anthocyanins (berries)
• 10 Dietary biomarkers and food records indicate compliance to study diets in the ADIRA (Anti-inflammatory Diet in Rheumatoid Arthritis) trial (2023) — Chronic inflammation
• 11 Effect of anti-inflammatory diets on health-related quality of life in adults with chronic disease: a systematic review and meta-analysis (2025) — Chronic inflammation
• 12 Nutraceutical enhancement of paraoxonase 1 activity in chronic inflammation: A systematic review of animal-based and plant-based nutraceuticals (2026) — Chronic inflammation
• 13 Prebiotic effect of lycopene and dark chocolate on the gut microbiome with systemic changes in liver metabolism, skeletal muscle and skin in moderately obese individuals (2019) — Cocoa flavanols
• 14 Markers of hypoxia and oxidative stress in ageing volunteers ingesting a lycosomal formulation of dark chocolate containing astaxanthin (2018) — Cocoa flavanols
• 15 Ingestion of a lycosome L-tug formulation of dark chocolate ameliorates postprandial hyperlipidaemia and hyperglycaemia in healthy volunteers (2019) — Cocoa flavanols
• 16 Dietary factors and supplements influencing prostate-specific antigen (PSA) concentrations in men with prostate cancer and increased cancer risk: An evidence review (2020) — Green tea and EGCG
• 17 Supporting prostate health with a novel nutraceutical compound possessing antioxidant properties: Results from a pilot study (2026) — Green tea and EGCG
• 18 The anticancer potential of plant-derived nutraceuticals via the modulation of gene expression (2022) — Green tea and EGCG
• 19 Evaluation of the anti-inflammatory effects of systemically administered curcumin, lycopene and piperine as an adjunct to scaling and root planing: A clinical study (2017) — Turmeric and curcumin
• 20 Efficacy of hyaluronidase combined with corticosteroids in the treatment of oral submucous fibrosis: A meta-analysis of randomised controlled clinical trials (2020) — Turmeric and curcumin
• 21 Efficacy and safety of a multi-ingredient liquid-based botanical nutraceutical for improving markers of metabolic health: A randomised, double-blind, placebo-controlled study (2026) — Turmeric and curcumin
• 22 Nutritional factors and physical frailty: Highlighting the role of functional nutrients in the prevention and treatment of frailty (2024) — Coenzyme Q10
• 23 Evaluation of monotherapy with coenzyme Q10, L-carnitine or combined therapy on semen parameters in idiopathic male infertility: A placebo-controlled, double-blind study (2026) — Coenzyme Q10
• 24 The role of antioxidants in the therapy of cardiovascular diseases: A literature review (2024) — Coenzyme Q10

5. Open Questions

• Dosage: What quantities of individual carotenoids are required for clinically relevant effects, and how do they interact with other micronutrients?
• Long-term effects: Are there robust data on multi-year intake, particularly for substances with limited human study evidence such as humic acid complexes?
• Target groups: Can subpopulations be identified that particularly benefit from carotenoids (e.g., in chronic inflammation or neurodegenerative diseases)?
• Combination therapies: What synergies exist between carotenoids and other compound classes (e.g., polyphenols or vitamins) in controlled studies?
• Biomarkers: Which surrogate parameters reliably correlate with clinical endpoints, and how can these be standardised?
• Environmental factors: How do light, temperature or processing methods affect the stability and efficacy of carotenoids in dietary supplements?

See also the gaps list across all substances. This page is recalculated with each update.