Nutrition and Eye Health Quiz

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.

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.