Carotenoids: α-Carotene, β-Carotene, β-Cryptoxanthin, Lycopene, Lutein, and Zeaxanthin.
Definition: Carotenoids are yellow, orange, and red pigments synthesized by plants. The most common carotenoids in North American diets are α-carotene, β-carotene, β-cryptoxanthin, lutein, zeaxanthin, and lycopene.
Provitamin A carotenoids, α-carotene, β-carotene, and β-cryptoxanthin, can be converted by the body to retinol (vitamin A). In contrast, no vitamin A activity can be derived from lutein, zeaxanthin, and lycopene.
- Dietary lutein and zeaxanthin are selectively taken up into the macula of the eye, where they absorb up to 90% of blue light and help maintain optimal visual function
- At present, it is unclear whether the biological effects of carotenoids in humans are related to their antioxidant activity and/or other non-antioxidant activities.
- Although the results of observational studies suggest that diets high in carotenoid-rich fruit and vegetables are associated with reduced risks of cardiovascular disease and some cancers, high-dose β-carotene supplements did not reduce the risk of cardiovascular disease or cancer in large randomized controlled trials.
- Two randomized controlled trials found that high-dose β-carotene supplements increased the risk of lung cancer in smokers and former asbestos workers.
- Recent meta-analyses of observational studies reported an inverse association between blood lycopene concentration and the risk of developing prostate cancer. To date, most small-scale intervention studies found little to no benefit of lycopene supplements in reducing the incidence or severity of prostate cancer in high-risk patients.
- Observational studies have suggested that diets rich in lutein and zeaxanthin may help slow the development of age-related macular degeneration (AMD). Randomized controlled trials found that lutein and zeaxanthin supplements could improve visual acuity and slow the progression to advanced AMD in subjects with AMD.
- Carotenoids are best absorbed with fat in a meal. Chopping, puréeing, and cooking carotenoid-containing vegetables in oil generally increase the bioavailability of the carotenoids they contain.
- The cholesterol-lowering agents, cholestyramine (Questran) and colestipol (Colestid) can reduce the absorption of fat-soluble vitamins and carotenoids, as can mineral oil and Orlistat (Xenical), a drug used to treat obesity.
- Colchicine, a drug used to treat gout, can cause intestinal malabsorption. However, long-term use of 1 to 2 mg/day of colchicine did not affect serum β-carotene concentrations in one study.
- Increasing gastric pH through the use of proton-pump inhibitors (Omeprazole, Lansoprazole) may decrease the absorption of a single dose of a β-carotene supplement.
Beta Carotene Dosage and administration
- Multivitamin formulas frequently provide 3–15 mg (5,000–25,000 IU) per day of beta-carotene. Daily doses up to 300 mg (500,000 IU) have been used to treat photosensitivity disorders.
- Beta-carotene absorption is enhanced by the presence of dietary fat. One study found that serum beta-carotene concentrations were significantly higher when 51 mg of beta-carotene was given in 3 divided doses per day than when it was given as a single daily dose.3
- Beta-carotene can be used to treat vitamin A deficiency,44 except in patients who have impaired conversion of beta-carotene to vitamin A. However, because the capacity of humans to convert beta-carotene to vitamin A is limited, beta-carotene would not be an effective treatment for conditions that require relatively high doses of vitamin A (such as various skin disorders and menorrhagia). In addition, administration of large doses of beta-carotene does not lead to vitamin A toxicity.
Lycopene Dosage and administration
- The optimal dosage of lycopene is not known. The dosages most frequently used in clinical trials have been 10–15 mg/day.
Lutein/Zeaxanthin Dosage and administration
- Dosages of lutein in clinical trials have usually ranged from 6–15 mg/day. There is little clinical research using zeaxanthin.
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