Understanding Antioxidants and Their Functions

Antioxidant

Substance that prevents oxidation -> neutralize or reduce the damage caused by naturally occurring oxidizing species.

Free radicals

Compounds with an unpaired electron at its outermost orbital.

Common targets for free radical damage

Cell membranes, Protein, Lipoproteins, Nuclear DNA.

Selenium

Trace mineral that spares the use of vitamin E and neutralizes free radicals.

Vitamin E

Helps maintain integrity of lipid (e.g. cell membranes) from damage caused by free radicals.

Vitamin C

Reactivates the deactivated vitamin E and can donate electrons to stabilize free radicals.

Vitamin A

Protects lipoproteins and cell membranes from damage caused by free radicals.

Key actions of nutrient antioxidants

Donate electrons to free radicals to stabilize it (vitamin C) and prevents cellular damage caused by oxidants (vitamin E and A).

Superoxide dismutase

Converts superoxide radical to oxygen (O2) and hydrogen peroxide (H2O2).

Catalase

Decomposes H2O2 into water (H2O) and O2.

Glutathione peroxidase

Reduces H2O2 to organic hydroperoxide (R-OOH) using glutathione as a reducing agent and protects cell membranes.

Physiological functions of Vitamin A

Needed to maintain a healthy cornea, acts on DNA to code for specific proteins in cells, and is needed by enzymes in osteoclasts to breakdown old bone.

Physiological functions of Vitamin C

Helps in iron absorption, helps in collagen synthesis, and re-activates vitamin E to its antioxidant form.

Physiological functions of Vitamin E

Reduces platelet aggregation, protects lipids such as cell membrane from free radical damage, and modulates T-cell function.

Physiological functions of Selenium

Co-factor for glutathione peroxidase and converts thyroxine to triiodothyronine.

Night blindness

Slow sight recovery from flashes of light under dim conditions.

Xerophthalmia

Dry eyes that can lead to cornea rupturing.

Scurvy

Condition characterized by weakness, random bruises, bleeding gums, loose teeth, and pinpoint hemorrhages.

Hemolytic anemia

Loss of integrity of red blood cell membranes leading to fatigue, lethargy, and shortness of breath.

Cardiomyopathy

Disease in the heart muscle characterized by fatigue, lethargy, and shortness of breath.

Hypothyroidism

Condition where selenium deficiency impairs the conversion of thyroxine to triiodothyronine.

Rich food sources of Vitamin A

Liver, egg yolks, broccoli, spinach, squash, yams, mango, and tomatoes.

Rich food sources of Vitamin C

Citrus fruits such as oranges, lemons, and berries.

Rich food sources of Vitamin E

Nuts (almonds, pumpkin, sesame), animals (egg yolks), and vegetables (parsley, asparagus, swiss chard).

Rich food sources of Selenium

Protein-rich foods, liver, meats, seafood, shellfish, eggs, whole grains, and mushrooms.

Beta-carotene

Naturally occurring plant pigment that is a precursor for retinal.

Retinal

Formed from the cleavage of beta-carotene and can be reduced to retinol.

Retinol

Form of vitamin A that can be oxidized to retinoic acid.

Antioxidant supplements concerns

Potential toxicity, with specific concerns for vitamins C, E, and selenium.

Vitamin A toxicity

Can cause pro-oxidant effects, enlargement of liver and spleen, and dry skin.

Vitamin C toxicity

Can lead to rebound scurvy, pro-oxidant effects, and kidney stones.

Vitamin E toxicity

Can cause muscle weakness and increase the effect of anticoagulants leading to uncontrolled bleeding.

Selenium toxicity

Can lead to increased incidence of diabetes in men and cause nausea and vomiting.

Antioxidants and cancer prevention

Antioxidants neutralize free radicals but do not prevent their formation; excessive intake can lead to cancer promotion.