Vitamin E Flashcards
Vitamin E forms
• 8 Vitamers
o 4 tocopherols: saturated side chains
o 4 tocotrienols: unsaturated side chains
o All have a hydroxyl group attached to C6 which provides the redox (antioxidant) potential
Vitamin E vitamer synonymous with Vitamin E
α-tocopherol
• Often synonymous with “vitamin E”
• Highest biological activity
• Only form of vitamin E officially recognized as being able to meet human requirements
Natural α-tocopherol
o RRR α-tocopherol (aka d-α-tocopherol)
o Biologically active form
Synthetic α-tocopherol
o All-rac-α-tocopherol (aka dl-α-tocopherol)
o Mixture of 8 stereoisomers
• RRR, RSR, RRS, RSS, SRR, SSR, SRS, and SSS (R first - biologically active, S first - not biologically active)
• Half of which are not biologically active
• 7 of 8 stereoisomers are not normally present in the human body
Vitamin E sources
• Unprocessed plant oils
o Primarily α-tocopherol: canola, olive, almond, sunflower, safflower and cottonseed
o Primarily α-tocopherol: walnut, soy, corn, flax
• Nuts and seeds
• Whole grains
• Legumes
• Leafy green vegetables
Vitamin E stability
• Oxidized with lengthy exposure to: oxygen, light or heat
Vitamin E digestion
- Tocopherols are found free in foods but synthetic ester forms require hydrolyzation prior to absorption with esterases
- Tocotrienols are found esterified in foods and therefore also require hydrolyzation
- All forms are fat soluble and require bile salts for micelle formation for emulcification and solubilization
- Simultaneous digestion of lipids improves the digestion of vitamin E
Vitamin E absorption
• Absorbed primarily in jejunum by passive diffusion
Vitamin E transportation
- Once inside the enterocyte tocopherols and tocotrienols are incorporated into chylomicrons for transport
- During transport they are transferred among lipoproteins which contain the highest amounts of vitamin E in circulation
- Chylomicron remnants bring the remaining vitamin E to the liver
- The liver then incorporates RRR-alpha-tocopherol in VLDLs for recirculation back into the blood and transport to other tissues
Vitamin E storage
• Stored mostly (>90%) in adipose tissues
Vitamin E functions
• Maintenance of membrane integrity
o Antioxidant function
• Free radical scavenging
• Destruction of singlet molecular oxygen
Vitamin E excretion
- Major route is thorough feces via bile
- Several metabolites excreted in urine
- Small amounts excreted through sebaceous glands in the skin
Who has increased requirements of vitamin E?
- Consumption of large amounts of PUFAs increases the requirement for vitamin E
- Those who smoke also have increased requirements
Vitamin E conversions
• RRR-α-tocopherol (d-α-tocopherol)
o 1 IU tocopherol = 0.67 mg α-tocopherol
o 400 IU of RRR-α-tocopherol = 268 mg α-tocopherol
• All rac-α-tocopherol (dl-α-tocopherol)
o 1 IU tocopherol = 0.91 mg α-tocopherol
o 400 IU of all rac-α-tocopherol = 364 mg α-tocopherol
Vitamin E deficiency symptoms
Rare in humans o Muscle pain and weakness o Ceroid pigment accumulation o Hemolytic anemia o Degenerative neurological problems
Vitamin E increased deficiency risk
o Adolescents
o Fat malabsorptive disorders
o Cigarette smokers
o Increased consumption of oxidized oils
Vitamin E clinical indications
• Heart disease
o α-tocopherol decreases oxidation of LDL by free radicals and γ-tocopherol inhibits platelet aggregation, both of which may prevent the development of atherosclerotic lesions and lower the risk of coronary heart disease
o Tocotrienols decrease cholesterol production decreasing plasma cholesterol levels
• Fibrocystic breast disease, Scleroderma, Dupuytren’s contracture, Peyronie’s disease, excess scarring
Vitamin E preparations
- Natural Vitamin E (RRR-α-tocopherol)
- Synthetic vitamin E (all-rac-α-tocopherol) is available in: α-tocopherol and α-tocopheryl acetate/succinate
- Water-miscible vitamin E
- Mixed tocopherols contain at least 20% other natural R,R,R- tocopherols,
- Mixed tocotrienols
Vitamin E toxicity
• UL = 1,000 mg α-tocopherol • Signs of toxicity: o Impaired blood coagulation o Nausea, diarrhea, flatulence o Muscle weakness o Fatigue o Double vision
Vitamin E nutrient interactions
- Vitamin C – Functions with vitamin E as part of antioxidant defense system
- Vitamin K – 2 metabolites of vit E have anti-vit K activity
Vitamin E assessment of status
• Plasma concentrations only correlate with intake in frank deficiency
• Erythrocyte hemolysis test
o A very crude test
o Compares the amount of hemoglobin released by RBCs during incubation with dilute hydrogen peroxide vs. sterile water
o However, variables other than vitamin E status influence in-vitro hemolysis
