Vitamin E

Question 1

Vitamin E forms

Answer 1

• 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

Question 2

Vitamin E vitamer synonymous with Vitamin E

Answer 2

α-tocopherol
• Often synonymous with “vitamin E”
• Highest biological activity
• Only form of vitamin E officially recognized as being able to meet human requirements

Question 3

Natural α-tocopherol

Answer 3

o RRR α-tocopherol (aka d-α-tocopherol)

o Biologically active form

Question 4

Synthetic α-tocopherol

Answer 4

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

Question 5

Vitamin E sources

Answer 5

• 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

Question 6

Vitamin E stability

Answer 6

• Oxidized with lengthy exposure to: oxygen, light or heat

Question 7

Vitamin E digestion

Answer 7

• 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

Question 8

Vitamin E absorption

Answer 8

• Absorbed primarily in jejunum by passive diffusion

Question 9

Vitamin E transportation

Answer 9

• 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

Question 10

Vitamin E storage

Answer 10

• Stored mostly (>90%) in adipose tissues

Question 11

Vitamin E functions

Answer 11

• Maintenance of membrane integrity
o Antioxidant function
• Free radical scavenging
• Destruction of singlet molecular oxygen

Question 12

Vitamin E excretion

Answer 12

• Major route is thorough feces via bile
• Several metabolites excreted in urine
• Small amounts excreted through sebaceous glands in the skin

Question 13

Who has increased requirements of vitamin E?

Answer 13

• Consumption of large amounts of PUFAs increases the requirement for vitamin E
• Those who smoke also have increased requirements

Question 14

Vitamin E conversions

Answer 14

• 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

Question 15

Vitamin E deficiency symptoms

Answer 15

Rare in humans
o	Muscle pain and weakness
o	Ceroid pigment accumulation 
o	Hemolytic anemia
o	Degenerative neurological problems

Question 16

Vitamin E increased deficiency risk

Answer 16

o Adolescents
o Fat malabsorptive disorders
o Cigarette smokers
o Increased consumption of oxidized oils

Question 17

Vitamin E clinical indications

Answer 17

• 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

Question 18

Vitamin E preparations

Answer 18

• 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

Question 19

Vitamin E toxicity

Answer 19

•	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

Question 20

Vitamin E nutrient interactions

Answer 20

• Vitamin C – Functions with vitamin E as part of antioxidant defense system
• Vitamin K – 2 metabolites of vit E have anti-vit K activity

Question 21

Vitamin E assessment of status

Answer 21

• 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