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Questions and Answers
What condition may benefit from beta-carotene supplementation?
What condition may benefit from beta-carotene supplementation?
What is the recommended daily intake of lutein for eye health?
What is the recommended daily intake of lutein for eye health?
What potential side effect can occur from excessive beta-carotene supplementation?
What potential side effect can occur from excessive beta-carotene supplementation?
Which carotenoids may slow the progression of age-related macular degeneration?
Which carotenoids may slow the progression of age-related macular degeneration?
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Which carotenoid is primarily sourced from tomatoes?
Which carotenoid is primarily sourced from tomatoes?
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What distinguishes humans from most animals regarding vitamin C?
What distinguishes humans from most animals regarding vitamin C?
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Where are the highest concentrations of vitamin C typically found in the human body?
Where are the highest concentrations of vitamin C typically found in the human body?
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What is the primary role of vitamin C in the context of DNA protection?
What is the primary role of vitamin C in the context of DNA protection?
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What can happen to vitamin C when it reacts with free radicals in the body?
What can happen to vitamin C when it reacts with free radicals in the body?
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Which of the following foods is NOT a significant source of vitamin C?
Which of the following foods is NOT a significant source of vitamin C?
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What is the recommended daily allowance of vitamin C for lactating women?
What is the recommended daily allowance of vitamin C for lactating women?
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Vitamin E is primarily recognized as a group of compounds known as:
Vitamin E is primarily recognized as a group of compounds known as:
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What percentage of vitamin E in human tissues is accounted for by α-Tocopherol?
What percentage of vitamin E in human tissues is accounted for by α-Tocopherol?
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What is the role of vitamin E in relation to lipid peroxidation?
What is the role of vitamin E in relation to lipid peroxidation?
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Which of the following components does NOT participate in the multi-component system with vitamin E?
Which of the following components does NOT participate in the multi-component system with vitamin E?
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Which food sources are particularly rich in alpha-tocopherol?
Which food sources are particularly rich in alpha-tocopherol?
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What is the primary function of selenium in relation to antioxidants?
What is the primary function of selenium in relation to antioxidants?
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What role does selenium play in relation to vitamin E?
What role does selenium play in relation to vitamin E?
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Which of the following is true about cyclobutane pyrimidine dimers (CPDs)?
Which of the following is true about cyclobutane pyrimidine dimers (CPDs)?
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In which tissue is most selenium stored in the human body?
In which tissue is most selenium stored in the human body?
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What is the stored form of retinol in the liver?
What is the stored form of retinol in the liver?
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What is a common result of UV radiation on human DNA?
What is a common result of UV radiation on human DNA?
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What is the recommended intake of beta-carotene for adult females?
What is the recommended intake of beta-carotene for adult females?
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Which nutrient intake is associated with the gene that codes for connexin proteins?
Which nutrient intake is associated with the gene that codes for connexin proteins?
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What is the RDA for beta-carotene based on the RDA for retinol activity equivalents (RAE)?
What is the RDA for beta-carotene based on the RDA for retinol activity equivalents (RAE)?
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How do high doses of beta-carotene affect skin sensitivity?
How do high doses of beta-carotene affect skin sensitivity?
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Which of the following nutrients can slow the progression of macular degeneration when taken together?
Which of the following nutrients can slow the progression of macular degeneration when taken together?
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What role does beta-carotene play in preventing cardiovascular diseases?
What role does beta-carotene play in preventing cardiovascular diseases?
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What is the RDA for an adult male in retinol activity equivalents (RAE)?
What is the RDA for an adult male in retinol activity equivalents (RAE)?
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What is a primary function of the thymus gland activated by beta-carotene?
What is a primary function of the thymus gland activated by beta-carotene?
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What role does selenium play in DNA protection?
What role does selenium play in DNA protection?
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Which of the following foods provides the highest amount of selenium?
Which of the following foods provides the highest amount of selenium?
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Which gene is classified as a tumor suppressor gene?
Which gene is classified as a tumor suppressor gene?
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How does the body use beta-carotene?
How does the body use beta-carotene?
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Which of the following is a non-provitamin A carotenoid?
Which of the following is a non-provitamin A carotenoid?
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Which carotenoid is synthesized by plants, algae, and photosynthetic bacteria?
Which carotenoid is synthesized by plants, algae, and photosynthetic bacteria?
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Which food is a good source of retinol vitamin A?
Which food is a good source of retinol vitamin A?
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What is the primary function of the proteins produced by the BRCA1 and BRCA2 genes?
What is the primary function of the proteins produced by the BRCA1 and BRCA2 genes?
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What is the process of beta-carotene breakdown catalyzed by?
What is the process of beta-carotene breakdown catalyzed by?
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Which carotenoid is known for its role as a precursor to Vitamin A?
Which carotenoid is known for its role as a precursor to Vitamin A?
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Study Notes
Nutrients That Protect DNA From Damage
- Vitamin C, also known as L-ascorbic acid, is a water-soluble vitamin found naturally in some foods, added to others, or available as a dietary supplement.
- Humans cannot produce vitamin C, making it an essential dietary component.
- The total body content ranges from 300 mg to 2 g.
- High levels of vitamin C (millimolar concentrations) are concentrated in cells and tissues, specifically leukocytes (white blood cells), eyes, adrenal glands, the pituitary gland, and the brain.
- Relatively low levels (micromolar concentrations) are found in extracellular fluids like plasma, red blood cells, and saliva.
Vitamin C
- Vitamin C plays a role as an antioxidant.
- Ascorbic acid neutralizes free radicals, producing a relatively unstable ascorbyl radical. This intermediate converts back into ascorbate and dehydroascorbate.
- Vitamin C reduces toxic reactive oxygen species such as superoxide anion (O₂⁰), hydroxyl radical (OH), organic radicals (RO₂), and nitrogen oxyradicals (NO₂).
- High intracellular concentrations prevent oxidation-induced mutations.
- Vitamin C transforms into a vitamin C radical during the process of destroying free radicals.
- In the presence of metal ions, vitamin C radical converts lipid hydroperoxides into geno-toxins that modify DNA bases, disrupting the DNA structure.
Dietary Sources of Vitamin C
- Citrus fruits, tomatoes, tomato juice, and potatoes are significant sources of vitamin C.
- Other good sources include red and green peppers, kiwifruit, broccoli, strawberries, Brussels sprouts, and cantaloupe.
Recommended Intake of Vitamin C
- The recommended daily allowance for adults is 90 mg for males and 75 mg for females.
- Pregnant women need 85 mg and lactating women need 120 mg.
- An additional 35 mg is recommended for smokers.
Vitamin E
- Vitamin E, also known as α-Tocopherol, is a group of eight lipid-soluble compounds, tocopherols, and tocotrienols, produced by plants.
- α-Tocopherol accounts for 90% of vitamin E in human tissues.
Structure of Vitamin E
- (The structure of α-tocopherol is shown as an image in the original text)
Antioxidant Activity
- Vitamin E is a lipid-soluble antioxidant that protects against lipid peroxidation.
- It participates in cellular systems with ascorbic acid, intracellular glutathione, glutathione reductase, and glutathione peroxidase.
Mechanism of Action
- Lipid-soluble vitamin E prevents lipid peroxidation chain reactions in cellular membranes (by interfering with the propagation of lipid radicals).
- Vitamin E inhibits the induction of "light" and "dark" cyclobutane pyrimidine dimers and oxidatively generated DNA damage in response to UVA.
Sources of Vitamin E
- Nuts, seeds, and vegetable oils are among the best sources of alpha-tocopherol.
- Significant amounts are available in green leafy vegetables and fortified cereals.
- Other excellent sources include animal products like cheese and eggs, or plant oils.
Selenium
- Selenium is a trace element that exists in inorganic forms (selenate and selenite) and organic forms (selenomethionine and selenocysteine).
- Most selenium exists as selenomethionine in animal and human tissues.
- Skeletal muscle is the main storage location, making up about 28% to 46% of the total selenium content.
Mechanism of Action
- Selenium is a part of glutathione peroxidase, a critical antioxidant enzyme that reduces free radicals and oxidation in the body.
- Selenium and vitamin E are synergistic antioxidants, meaning they work better together than separately.
- Selenium supports the activity of vitamin E in preventing the oxidation of fats.
- Selenium works effectively alongside vitamin C, glutathione, and vitamin B3 (niacin) to prevent oxygen molecules from becoming excessively reactive.
- Selenium may protect DNA by increasing the activity of DNA repair enzymes, such as DNA glycosylases, and pathways such as p53 and BRCA1.
Sources of Selenium
- Brazil nuts are a rich source of selenium (544 mcg or 777% DV per ounce).
- Other sources include tuna, halibut, brown rice, eggs, and white bread.
Carotenoids
- Carotenoids are naturally occurring fat-soluble pigments produced by plants, algae, and photosynthetic bacteria.
- They are classified into carotenes (e.g., beta-carotene, lycopene) and xanthophylls (e.g., lutein, zeaxanthin).
Classification of Carotenoids
- Provitamin A carotenoids include alpha-carotene, beta-carotene, and beta-cryptoxanthin.
- Non-provitamin A carotenoids include lutein, zeaxanthin, and lycopene.
Vitamin A Types
- Vitamin A from animal sources is called retinol, a pre-formed vitamin A directly usable by the body.
- Sources include beef and chicken liver, whole milk, and cheese.
- Vitamin A from fruit and vegetables exists as provitamin A carotenoids, which the body converts to retinol after ingestion.
- Sources include carrots, sweet potatoes, spinach, and kale.
Beta-carotene
- Beta-carotene, also known as provitamin A, is one of the most significant precursors of vitamin A in the diet.
- Beta-carotene converts to vitamin A via cleavage at the centre or by breaking down from one end of the molecule.
- (Beta-carotene structure is shown in an image)
- The breakdown of beta-carotene in the small intestine walls is catalyzed by beta-carotene dioxygenase. The resulting retinol is stored in the liver as retinyl esters.
Absorption
- Beta-carotene is fat-soluble, so absorption is enhanced when taken with meals containing at least 3 g of fat.
- After digestion, beta-carotene is apparent in plasma, initially chylomicrons (fat particles in blood serum), and then VLDL, later LDL, and HDL.
Beta-carotene Intake
- The recommended intake, according to the National Institutes of Health, is 3000 IU for adult males and 2310 IU for adult females.
- To convert from micrograms (μg) of beta-carotene to retinol activity equivalents (RAE), multiply by 12.
Unique Feature of Carotenoids
- Carotenoids improve intercellular communication by enhancing connexin protein expression.
- Connexin proteins form pores/gap junctions in cell membranes, allowing small molecules to pass between cells.
- Carotenoids protect DNA via activation of repair mechanisms.
Lutein and Zeaxanthin
- Lutein and zeaxanthin are yellow-to-red carotenoids found widely in plants and vegetables.
- They are concentrated in the macula of the eye, giving it a yellowish tone.
- They form a protective macular pigment layer that filters blue light to protect the eye.
- Humans cannot produce them naturally; they are acquired through diet and/or supplementation.
- Recommended intake for eye health is 10 mg/day for lutein and 2 mg/day for zeaxanthin.
Lycopene
- Lycopene is a red carotenoid predominantly found in tomatoes and some other fruits/vegetables.
- It is a potent inhibitor of cancer cell proliferation by regulating the cell cycle.
- Lycopene prevents malignant transformation.
- Humans cannot produce it naturally, requiring it from the diet.
Benefits of Carotenoids
- Consumption of beta carotenoids could potentially slow down the progression of macular degeneration.
- Beta carotene can reduce the risk of cardiovascular disease by reducing the oxidation of LDL cholesterol, thereby lowering the chance of atherosclerosis and coronary heart disease
- Beta carotene strengthens the immune system by activating the thymus gland which is one of the most important sources of immune protection.
- High dosages of beta-carotene can reduce sunburn and offer an SPF effect.
Intake Levels
- For eye health, recommended daily intake for lutein is 10 mg, while for zeaxanthin, it's 2 mg.
Side Effects of Beta-carotene Supplements
- Beta-carotene supplements may pose risks to pregnant and breastfeeding women.
- Side effects may include skin discoloration (yellowing), loose stools, bruising, and joint pain.
Anthocyanins and Anthocyanidins
- Anthocyanins are a group of red-blue plant pigments found mainly in flowers and fruit, but also in leaves and stems.
- Anthocyanins' color depends on acidity; they are red at acidic levels and blue at less acidic levels.
- Sources of anthocyanins include berries, eggplants, avocado, oranges, elderberries, olives, red onion, fig, sweet potato, and purple corn.
Anthocyanins Potential Uses
- Anthocyanins, extracted from plants, are food additives such as E163.
- E163 is a purple food colouring used in confections, jam, and beverages.
Mechanism of Action of Anthocyanins
- Anthocyanins act by suppressing reactive species formation through enzyme inhibition or the sequestration of trace elements, preventing free radical production.
- They are effective antioxidants against cytotoxicity and DNA single-strand breaks (SSB), impacting lipid peroxidation.
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Description
Test your knowledge on carotenoids and their impact on eye health. This quiz covers key nutrients such as beta-carotene and lutein, along with their recommended intakes and potential effects. Understand how these compounds contribute to overall vision wellness.
