Flashcards in 5) Fat, Carbohydrate, Water, Mineral, Electrolyte, and Vitamin Requirements in Adulthood (Part II) Deck (37)
What are the major functions of vitamin A?
Required for proper vision, gene expression, reproduction, embryonic development, growth, and immune function
What factor determines the requirement for vitamin A?
- Based on the amount of dietary vitamin A required to maintain a given body-pool size in well-nourished subjects
- To assure that vitamin A reserves cover increased needs during periods of stress and low-vitamin A intake
Where may preformed vitamin A be acquired?
Certain animal-derived foods
Where are provitamin A carotenoids found?
- Darkly coloured fruits and vegetables
- Oily fruits
- Red palm oil
1 ug of RAE (or 1 ug of retinol) is equal to which quantities of dietary provitamin A carotenoids, in terms of B-carotene, a-carotene, and B-cryptoxanthin?
- B-carotene: 12 ug
- a-carotene: 24 ug
- B-cryptoxanthin: 24 ug
What are the two major functions of vitamin D?
1) Enhances absorption efficiency of calcium and phosphorus within the small intestine
2) Produces potent anti-proliferative and pro-differentiation effects in a variety of tissues
How is vitamin D implicated in cancer and tumour cells?
Vitamin D may prevent the dysregulation from occurring through its anti-proliferative effects, halting the progression of tumour cells
What is vitamin D2?
What are sources of vitamin D2?
Yeast and plant sterols
What is vitamin D3?
What are sources of vitamin D3?
Derived from 7-dehydrocholesterol when it is synthesized in the skin
How does the requirement for vitamin D vary with age?
The requirement increases after reaching 70 years of age
What is the major function of vitamin E?
Functions as a non-specific chain-breaking antioxidant preventing the propagation of lipid peroxidation
What factor determines the requirement for vitamin E?
- The correlation between hydrogen peroxide-induced erythrocyte lysis and blood a-tocopherol
- Analysis of the level of a-tocopherol that protects against hemolysis caused by hydrogen peroxide
What are the four naturally-occurring tocopherol structures that have vitamin E antioxidant activity? How many methyl groups do they possess?
- α-tocopherol (trimethyl)
- β-tocopherol or γ-tocopherol (dimethyl)
- δ-tocopherol (monomethyl)
Are the forms of vitamin E interconvertible?
No, they are not interconvertible
What is the characteristic structure of tocopherols?
Substituted hydroxylated ring system (chromanol ring) with a long, saturated (phytyl) side chain
What is the difference between tocopherols and tocotrienols?
- The side chain of tocopherols are saturated
- The side chain of tocotrienols are unsaturated
Where are the synthetic forms of vitamin E contained?
Fortified foods or supplements
What characterizes the stereochemistry of synthetic vitamin E?
A synthetic mixture (all racemic) form, producing equal amounts of the possible stereoisomers
How many stereoisomers are there for tocopherol? How do they differ?
- 3 asymmetric carbon atoms
- 8 possible stereoisomers, which are not treated equally by the human body
What is the stereochemistry of a vitamin E supplement that is derived from a "natural source of vitamin E"? How?
- Derived by methylation of γ-tocopherol isolated from vegetable oil
The DRI definition of vitamin E is related to which stereoisomeric forms?
- 2R-stereoisomeric forms
- In which carbon at position 2 is an R carbon
What are the four types of 2R-stereoisomeric forms?
How does the activity of rac-a-tocopherol supplements differ from the activity of RRR-a-tocopherol from food and 2R forms of tocopherol?
Rac-a-tocopherol contains half of the activity
The RDA for vitamin E is 15 mg/day. How may it be acquired from RRR-a-tocopherol, 2R-stereoisomeric forms, or all rac-a-tocopherol?
- RRR-a-tocopherol: 15 mg/day
- 2R-stereoisomeric forms: 15 mg/day
- Rac-a-tocopherol: 30 mg/day
The concentration of the various forms of vitamin E in plasma are dependent on what?
Their affinity with hepatic a-tocopherol transfer protein (a-TTP)
a-TTP affinity is highest in which form of vitamin E?
How does a poor affinity for SRR-a-tocopherol and natural γ-tocopherol affect lipid metabolism?
They are poorly packaged into lipoproteins for delivery to peripheral tissue given their poor affinity