Vitamin C (Ascorbic Acid)
If a person takes two 500mg vitamin C supplements, how much will be absorbed?
50% Since: absorption is <50% with intakes over 1g.
List the functions of vitamin C:
1)Redox reactions: -involving iron (Fe) and copper (Cu) -antioxidant (reducing agent) 2)Collagen Synthesis 3) Neurotransmitter Synthesis -dopamine -serotonin 4) PRO oxidant potential at high levels
What forms of vitamin C are found in supplements?
"Free ascorbic acid", calcium ascorbate, sodium aschorabte, and ascorbyl palmitate.
Describe four adverse reactions that may result if intake exceeds the UL.
-toxicity is more likely -abdominal pain and osmotic diarrhea -increased risk of kidney stones for people with renal disease -increased risk of iron toxicity for those with disorders of iron metabolism.
If intake is substantially higher or lower how does that affect % absorption?
Absorption of vitamin C DECREASES with INCREASED intake. <50% with intakes over 1g.
What is the RDA for vitamin C? a. Adult men: b. Adult women: c. Smokers:
Adult Men: 90mg/d Adult Women: 75mg/d Smokers: Recommended + 35mg/d. *Smokers need more than the recommended amount.
What form of vitamin C is the major one found in foods?
Ascorbic Acid
Which isomer form of ascorbic acid is biologically active?
L-isomer (In humans)
List the symptoms associated with scurvy. What are most of these symptoms related to?
Bleeding gums, poor wound healing, petechiae (red dots under the skin). Most of these symptoms are related to poor collagen formation.
Briefly describe the evidence for the role of vitamin C in the following disorders as described in the text:
COLDS: Enhance immunity by promoting chemotaxis and proliferation of some immune cells. Destroys histamine. Increases the activity of natural killer cells. CANCER: Increased intake of fruits/veggies, decreases the risk of some cancers. Exhibits protective effects. CVD: Increased intake of fruits/veggies are associated with decreased risk of heart disease. EYE HEALTH: Decreased age-related macular degeneration.
List the major food sources of vitamin C and some specific examples OTHER than citrus.
Fruits: Kiwi, strawberries, cantaloupe. Vegetables: Tomato, Broccoli, Peppers Book includes: Cauliflower, Brussels sprouts, kale.
What environmental conditions destroy vitamin C?
Heat, light, oxidation, alkaline solutions
What animals are unable to synthesize vitamin C?
Including humans, primates, fruit bats, guinea pigs, and some birds.
What is the normal plasma level of ascorbic acid?
~ 0.4 mg - 1.7 mg/dL
If vitamin C intake is in the normal range (30 - 180 mg/d), what percentage is absorbed?
~ 70-90%
Does vitamin C need to be digested before absorption? If so, how?
No need to be digesting, it is directly absorbed.
If you suspected that a client had a vitamin C deficiency, what biochemical tests would you need to request to confirm your suspicion?
Plasma vitamin C concentrations. Plasma levels below 0.2 mg/d are considered to be deficient.
How is vitamin C excreted?
Through urine.
Describe the major interaction with Vitamin C and Fe in the GI.
Vitamin C enhances the absorption of nonheme iron either by reducing iron to a ferrous (Fe2+) state from a ferric (Fe3+) state or by forming a soluble complex with the reduced iron in the alkaline pH of the small intestine. Vitamin C rich foods + nonheme iron-rich foods = better absorption.
What is ascorbate?
Vitamin C; at physiological pH in its ionized form
When does the vitamin C deficiency disorder scurvy develop?
When intake is < 10mg/d.
What enzyme is lacking in these animals?
gulunolactase oxidase (the last enzyme in the vitamin C synthetic pathway).
Who is likely to develop scurvy?
-Alcohol/illegal drug users -poor oral food intake -institutionalized individuals especially the disabled and elderly.
How is scurvy treated?
-Rarely with food. -provide supplements -the standard: 100-300mg/d ~ 3 months.
What is the UL for vitamin C?
2 grams
