Carotenoid – Function, Sources and Health
Carotenoids are natural pigments found in plants that act as antioxidants and play important roles in human health, including supporting vision and immune function.
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Carotenoids are natural pigments found in plants that act as antioxidants and play important roles in human health, including supporting vision and immune function.
What Are Carotenoids?
Carotenoids are a group of over 700 known fat-soluble natural pigments produced by plants, algae, fungi, and certain bacteria. They are responsible for the yellow, orange, and red colours found in many fruits and vegetables. Well-known examples include beta-carotene, lycopene, lutein, zeaxanthin, and astaxanthin. The human body cannot synthesise carotenoids and therefore depends on dietary intake.
Biological Functions
Carotenoids fulfil several important roles in the human body:
- Provitamin A activity: Certain carotenoids such as beta-carotene, alpha-carotene, and beta-cryptoxanthin can be converted by the body into vitamin A (retinol), which is essential for vision, immune function, and cell growth.
- Antioxidant activity: Carotenoids neutralise free radicals and protect cells from oxidative stress, which is linked to ageing and chronic disease.
- Anti-inflammatory effects: Some carotenoids can help reduce inflammatory processes in the body.
- Eye and skin protection: Lutein and zeaxanthin accumulate in the retina of the eye, protecting against light-induced damage and age-related macular degeneration.
Dietary Sources
Carotenoids are found in a wide variety of plant-based foods. The best dietary sources include:
- Beta-carotene: Carrots, sweet potatoes, pumpkin, mangoes, apricots, spinach, kale
- Lycopene: Tomatoes (especially cooked), watermelon, pink grapefruit, papaya
- Lutein and zeaxanthin: Kale, spinach, corn, peas, egg yolk
- Astaxanthin: Salmon, shrimp, crab, trout (derived from microalgae in their diet)
- Beta-cryptoxanthin: Red and orange bell peppers, tangerines, pumpkin
Because carotenoids are fat-soluble, their absorption in the gut is significantly improved when consumed alongside a small amount of healthy fat (e.g., olive oil). Gentle cooking or pureeing vegetables (e.g., tomatoes) can also increase bioavailability.
Recommended Intake
There is no single universal recommended daily intake for carotenoids as a group. The World Health Organization (WHO) and national nutrition authorities recommend a varied diet rich in fruits and vegetables to ensure adequate carotenoid intake. Guidance on provitamin A activity is based on vitamin A requirements: adults are generally advised to consume approximately 700–900 µg of retinol equivalents per day.
Deficiency and At-Risk Groups
An isolated carotenoid deficiency is uncommon. However, certain groups may be at risk of insufficient intake:
- People with a very limited or low-calorie diet
- Individuals with conditions that impair fat absorption (e.g., Crohn's disease, coeliac disease, cystic fibrosis)
- Smokers (increased oxidative stress and altered carotenoid metabolism)
- Older adults with reduced food intake
Insufficient beta-carotene can indirectly contribute to vitamin A deficiency, which may manifest as night blindness, dry skin, and increased susceptibility to infections.
Toxicity and Overdose
Carotenoids from food sources are considered safe, even at high intake levels. However, very high consumption of beta-carotene may lead to a harmless and reversible yellowing of the skin known as carotenodermia. Importantly, high-dose beta-carotene supplements are not recommended for smokers and former smokers, as clinical trials (the ATBC and CARET studies) found an increased risk of lung cancer with supplementation in these groups. Vitamin A toxicity from food-derived carotenoids alone is not a concern, as the conversion to vitamin A is regulated by the body.
Carotenoids and Health – Scientific Evidence
Numerous observational studies suggest associations between high dietary carotenoid intake and a reduced risk of:
- Cardiovascular disease
- Certain cancers (e.g., prostate cancer and lycopene)
- Age-related macular degeneration (lutein and zeaxanthin)
- Metabolic syndrome and type 2 diabetes
However, intervention trials using isolated carotenoid supplements have produced less consistent results compared to dietary studies. Experts therefore recommend obtaining carotenoids primarily through a varied, plant-rich diet rather than through supplements.
References
- Britton, G., Liaaen-Jensen, S., Pfander, H. (Eds.) – Carotenoids: Handbook. Birkhäuser Verlag, Basel, 2004.
- World Health Organization (WHO) – Vitamin and Mineral Requirements in Human Nutrition, 2nd edition, 2004. Available at: https://www.who.int
- Krinsky, N.I., Johnson, E.J. – Carotenoid actions and their relation to health and disease. Molecular Aspects of Medicine, 26(6), 459–516, 2005. PubMed PMID: 16309738.
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