Carotenoids Flashcards
Provitamin A carotenoids
o α-carotene
o β-carotene
o γ-carotene
o β-cryptoxanthin
Non-provitamin A carotenoids
o Lycopene
o Lutein
o Zeaxanthin
o Astaxanthin
β-carotene
- Red-orange pigment
- Lipid soluble
- Abundant in plants and fruit
- Converted to vitamin A in the body
β-carotene sources
- Brightly coloured (orange and yellow) fruits and vegetables
- Green leafy vegetables
β-carotene absorption
- Absorbed in the duodenum and jejunum primarily by cartenoid transporters at low concentrations and by passive diffusion at high concentrations
- Enhanced by gastric acid and the presence of dietary fat
- Inhibited by pectin and excessive vitamin E consumption
β-carotene metabolism
• β-carotene can be metabolized in enterocytes to form retinol
o This process depends on the vitamin A status and the amount and forms of carotenoids consumed
• 1 mcg of retinol is formed from:
o 12 mcg β-carotene
o 24 mcg α-carotene or β-cryptoxanthin
β-carotene transport
- Like vitamin A, β-carotene is transported in chylomicrons to extrahepatic tissues and then what is remaining is brought to the liver
- β-carotene can then be packaged for further transport as part of VLDL or other lipoproteins to tissues
β-carotene storage
• β-carotene is stored in liver and adipose tissue
β-carotene functions
- Antioxidant
* Regulation of cell proliferation, growth and differentiation
β-carotene excretion
• Metabolized to variety of compounds and excreted into the bile
β-carotene requirements
• None established
o Not an essential nutrient
o No documented deficiency syndrome
• Vitamin A deficiency may occur in people whose diet is low in both vitamin A & β-carotene
β-carotene increased risk of deficiency
o Patients with fat malabsorption
o People who sunburn frequently
o Cigarette smokers
o Excessive alcohol consumption
β-carotene clinical indications
- Photosensitivity
- Sunburns
- Vitamin A deficiency
β-carotene preparations
• Synthetic
o 95-100% all-trans β-carotene
o Almost all clinical studies use this form
• Natural
o Derived from algae (Dunaliella salina)
o 50% trans beta-carotene and several other forms
o Appears to be a more potent lipophilic antioxidant than the synthetic all-trans form
β-carotene toxicity
• Carotenoids have less toxicity than vitamin A
o No UL established
o β-carotene is listed on the FDA GRAS list
o Large doses of β-carotene do not lead to vitamin A toxicity
o No adverse effects reported with large doses (up to 180 mg/d for 5 years)
• Hypercarotenosis and carotenodermia
o >30 mg/d of carotenoids may cause a harmless yellow-orange discoloration of the skin
o May also be seen in:
• Hypothyroidism, diabetes, renal failure, liver disease, anorexia nervosa, or a genetic defect in the capacity to convert β-carotene to vitamin A
• In cigarette smokers
o β-carotene supplementation has been shown to increase the risk of lung cancer in smokers
o Decreased effectiveness of radiation therapy?
o May also increase cancers of the:
• Head & neck, urinary tract, digestive tract, cervix, thyroid, and ovaries (observational studies)
• In Alcoholics
o May increase the hepatotoxicity of ethanol (animal study)
β-carotene nutrient interactions
- Vitamin A – high doses of β-carotene for extended periods may induce a vitamin A deficiency
- Vitamin E – high doses of β-carotene may decrease serum vitamin E levels
- Plant sterols – decrease absorption of beta-carotene
