Carotenoids – Colourful Plant Compounds with Proven Effects on Eyes, Skin and Metabolism

They give carrots their orange colour, tomatoes their vivid red and autumn leaves their golden splendour: carotenoids are among nature's most fascinating plant compounds. For a long time they were seen mainly as vitamin A precursors and antioxidants. But current research in 2025 and 2026 paints a more complex picture – carotenoids such as lutein, zeaxanthin and lycopene act as signalling molecules that intervene in gene expression. From eye health to the skin's protection against light to metabolism, the scientific evidence for these colourful plant compounds is growing rapidly.

What are carotenoids? An introduction to the natural colour pigments

Carotenoids are fat-soluble colour pigments produced by bacteria, fungi and plants. Humans cannot synthesise them and depend on dietary intake. Over 750 different carotenoids have been identified to date; around 50 are detectable in human blood. Two main groups are distinguished:

• Carotenes (pure hydrocarbons): β-carotene (carrots), α-carotene and lycopene (tomatoes)
• Xanthophylls (oxygen-containing derivatives): lutein and zeaxanthin (green leafy vegetables, corn) and β-cryptoxanthin (oranges, peppers)

For a long time their role as vitamin A precursors took centre stage – β-carotene in particular is converted into retinol in the body. But this view falls short. Carotenoids exert their effects through several mechanisms at once: as direct antioxidants neutralising reactive oxygen species, as filters for high-energy blue light, and as regulators of gene expression via transcription factors such as NF-κB and Nrf-2.

Carotenoids and eye health – the retina's natural sunglasses

The best-researched effect of carotenoids concerns eye health. Lutein and zeaxanthin hold a special position: they are the only carotenoids selectively concentrated in the macula (yellow spot) of the retina – at concentrations around a thousand times higher than in the blood. This concentration serves two protective functions: filtering out high-energy blue light and neutralising free radicals that can damage the sensitive photoreceptors.

The AREDS studies on age-related macular degeneration

Since the major AREDS studies (Age-Related Eye Disease Study), it has been considered established that high-dose antioxidants combined with lutein and zeaxanthin can slow the progression of dry age-related macular degeneration (AMD) at the intermediate to advanced stage. The AREDS2 study confirmed the safety and benefit of supplementation with 10 mg lutein and 2 mg zeaxanthin in patients at high AMD risk. Important: these effects are documented for existing AMD; a direct transfer to healthy eyes is not proven.

Intake in Switzerland, Germany and Austria

In German-speaking countries, daily intake is only around 1–2 mg lutein and 0.1–0.2 mg zeaxanthin. Since only about 15% of women and 7% of men reach the recommended five portions of vegetables and fruit per day, intake can be assumed to be rather low. The German Ophthalmological Society recommends a Mediterranean diet with red, yellow and green vegetables as well as oily fish and olive oil.

Carotenoids for the skin – light protection from within

Carotenoids protect not only plants and algae from intense sunlight but also exert a photoprotective effect in humans. Studies show that supplementing around 20–25 mg of carotenoids daily over eight to twelve weeks can reduce skin reddening after UV exposure by 20–30% – a protective effect corresponding to a moderate increase in the body's own light protection. Important: this does not replace sun protection but at most complements it from within.

A twelve-week application of natural carotenoids combined with selenium and vitamin E also measurably increased skin density and thickness and improved surface structure. The bioavailability of carotenoids can be enhanced by combining them with vitamin E (α-tocopherol) or vitamin C – an indication of synergistic effects.

Carotenoids and cognitive health – protection for the brain?

A 2022 study published in Neurology (Beydoun et al., PMID 35508396) examined the relationship between carotenoid blood levels and dementia risk in 7,283 people over an average of 16–17 years. The result: higher serum levels of lutein, zeaxanthin and β-cryptoxanthin were associated with a lower risk of dementia.

Important context: the effect weakened once factors such as education, income and physical activity were taken into account. This means these lifestyle factors may explain part of the association. This is an observational study – it shows an association, not causation. The authors expressly emphasise that randomised trials are needed to demonstrate a causal neuroprotective effect.

Carotenoids and metabolism – new findings on fat burning

A review published in January 2026 in Current Obesity Reports (Aygun et al., DOI 10.1007/s13679-025-00684-2) examined the effects of vitamin A derivatives and carotenoids (β-carotene, lycopene, lutein, β-cryptoxanthin) on adipose tissue. The findings: compounds such as retinoic acid, lycopene, β-cryptoxanthin and zeaxanthin reduce fat cell formation and fat synthesis in models by suppressing key transcription factors (PPARγ, C/EBPα, SREBP1-c). At the same time they promote the conversion of white into beige adipose tissue – so-called "browning" – thereby increasing heat production (thermogenesis).

This effect is mediated through the activation of AMP-activated protein kinase (AMPK) and the upregulation of thermogenic genes such as UCP1 and PGC-1α. Important caveat: this review evaluates exclusively in vitro and animal studies. Transferability to humans has not been established – the results open research perspectives but are no basis for concrete weight-loss recommendations.

The most important carotenoids and their food sources

Since carotenoids are fat-soluble, their absorption depends heavily on simultaneous fat intake. The ideal combination is colourful vegetables with high-quality oils or oily fish. For lycopene and β-carotene, heating additionally improves bioavailability.

Safety – what to keep in mind

Despite the largely positive evidence, a differentiated view is needed: individual intervention studies have shown that high doses of isolated β-carotene can increase lung cancer risk in smokers. High-dose single-substance preparations are therefore not advisable – especially for smokers. Carotenoids from a varied, plant-rich diet, by contrast, are considered safe and beneficial.

Conclusion

Carotenoid research has expanded our understanding of these colourful plant compounds: they are more than antioxidants or vitamin A precursors. Best documented is the importance of lutein and zeaxanthin for eye health. The findings on skin, cognition and metabolism are promising but rest partly on observational, animal or laboratory studies and are not yet clinically confirmed.

For everyday life, the simplest and safest strategy remains: a colourful, plant-rich diet with plenty of vegetables and fruit, combined with high-quality fats. For certain risk groups – older people, those with low vegetable intake – targeted supplementation may be useful, ideally as part of a balanced micronutrient approach.

This article is intended for general informational purposes only and does not replace medical advice. Dietary supplements are not a substitute for a balanced and varied diet.