Chapter 8-9: Vitamins Flashcards
List the Water-Soluble Vitamins.
1) B vitamins
2) Vitamin C
What is the shape of the curve on a graph representing the bodily harm in relation to the amount of a nutrient that is absorbed?
U-shape
List the fat-soluble vitamins.
1) Vitamin A
2) Vitamin D
3) Vitamin E
4) Vitamin K
List the different types of B vitamins.
Thiamin (B1) Riboflavin (B2) Niacin (B3) Biotin Pantothenic acid Vitamin B6 Folate Vitamin B12
Smokers have a higher requirement of which vitamin?
Vitamin C
What are fortified foods?
Foods to which nutrients have been added to…
i) replace nutrients lost during processing (enrichment)
ii) increase the amount of a nutrient in the food supply
When does a nutrient HAVE to be listed in the nutrients facts table?
- when it has been added to a food
What is the UL for Vitamin C?
2,000mg
What is bioavailability?
- how much of a nutrient can be absorbed and used in the body
How are fat-soluble and water-soluble vitamins absorbed differently in the body?
i) fat-soluble vitamins are incorporated into micelles in the small intestine and then absorbed by simple diffusion
- once inside the mucosal cells, they are packaged in chylomicrons, which enter the lymph before passing into the blood
ii) water-soluble vitamins are absorbed directly from the small intestine into the blood
How are water-soluble vitamins stored and excreted?
- they are not stored (w. exception of B12 which can stay in body for yrs)
- excess excreted through urine
- deplete more quickly than fat-soluble
How is an active vitamin created?
when the vitamin combines with a chemical group to form the functional coenzyme
How is an active coenzyme created?
when a functional coenzyme combines with an incomplete enzyme
Which vitamins help with energy metabolism function?
Thiamin Riboflavin Niacin Pantothenic Acid Biotin
Which vitamins help with single carbon metabolism function?
B6
Folate
B12
What is an antioxidant?
- nutrient that protects from oxidative damage/stress
Which vitamins function as antioxidants?
Vitamin C
Vitamin E
What disease is attributed to a deficiency in Thiamine? Where is it most common?
BERIBERI
- common in pop’ns where unenriched white rice is a staple
What are some of the symptoms of Beriberi?
- weakness
- nerve tingling
- poor co-ordination
- paralysis
- death
____ depletes thiamine.
Alcohol
- Wernicke-Korsakoff syndrome
What is the best source of riboflavin in the Canadian diet? How can it be destroyed?
- milk
- riboflavin can be destroyed by light
Which disease is caused by a deficiency in niacin? In which diets is it most common and why?
Pellegra
- diets high in corn –> niacin is bound to protein (not bioavailable)
note: in S America, corn is treated w. lime, which releases bound niacin
What are the symptoms of pellegra?
The 4 D’s:
1) Dermatitis
2) Diarrhea
3) Dementia
4) Death
From which amino acid can niacin be synthesized from?
Tryptophan
What is the UL of Niacin?
35mg
Which disease is niacin used to treat? Why?
Cardiovascular Disease (in doses of 50mg –> side effects)
- lowers LDL cholesterol
- raises HDL cholesterol
- lowers serum triglycerides
What is homocysteine?
- an amino acid that is toxic to blood vessels
- high levels increase the risk of cardiovascular disease
What is the homocysteine hypothesis?
- increasing intake of B6, B12, and folate keeps homocysteine levels in the blood low
- reduces risk of cardiovascular disease
How does vitamin B6 lower homocysteine levels?
- by helping to convert homocysteine to cysteine
How do folate and vitamin B12 lower homocysteine levels?
- by converting homocysteine to methionine
- achieved by transfer of a methyl group from methyl folate to B12, forming methyl-B12
What function does folate serve in the body?
single carbon metabolism
- synthesis of the components of DNA
- DNA methylation (controls gene expression)
What may a folate deficiency result in?
Megaloblastic/Macrocytic Anemia
What may a folate deficiency result in for a pregnant woman? Why?
Neural tube defects in their child
- folate needed for neural tube closure, which develops into the brain & spine
Why is a folate deficiency so risky for women who are at childrearing age?
neural tube closure occurs between day 20-28 after conception - a time before many women know that they are pregnant
- thus, food is often fortified w. folate to help prevent this; also recommended to take at least 400ug of folate/day
What is pernicious anemia?
- caused by an inability to absorb sufficient B12
- due to autoimmune disease which destroys the cells that produce IF (intrinsic factor)
- symptomatically same as megaloblastic anemia but does not respond to iron supplementation
B12 is required for the formation of which part of the cell?
MYELIN SHEATH
What is atrophic gastritis?
- inflammation of stomach lining that results in reduced secretion of stomach acid & bacterial overgrowth
- prevents release of protein bound B12
- severe cases interfere with production of IF
What is the UL for folate?
1,000ug
What may mask a vitamin B12 deficiency? Why is this dangerous?
- excessive in take of folic acid may mask a B12 deficiency
- dangerous b/c although anemia does not develop, the neurological damage continues
What is oxidative stress?
- when there are more reactive oxygen species than can be neutralized by antioxidants in the body
- damage to protein, DNA, membranes, LDL cholesterol
What are some sources of reactive oxygen species?
1) Mitochondrial energy metabolism
2) Dropped electrons
3) Superoxide conversion to hydrogen peroxide
How do antioxidants neutralize free radicals?
by donating electrons
Why is the vitamin C requirement for smokers higher than for non-smokers?
- smoking generates free radicals in lung tissue
- Vitamin C neutralizes these free radicals
Which disease is caused by a vitamin C deficiency?
scurvy
What are the 3 main functions of vitamin A?
1) Visual cycle
2) Gene expression
3) Cell differentiation
How are Canadians doing with respect to their intake of Vitamin A (from food)?
not good - high prevalence of inadequate intake
What is retinol?
pre-formed vitamin A
- from animal sources
- interconvertable with retinal
Can retinoic acid be converted back to other forms once converted?
NO
____ can be converted into retinol. Is this conversion efficient?
Beta-carotene
- conversion is inefficient b/c (i) not all beta-carotene is absorbed, and (ii) not al beta-carotene is converted to retinol
- 1ug RAE = 12ug beta-carotene from food
Beta-carotene acts as a(n) ______.
ANTIOXIDANT
- circulates in the blood
- observational studies suggest that high levels of beta-carotene reduce risk of lung cancer in smokers
- intervention trial suggests the opposite –> may have given too high of a dose of beta-carotene (hypercarotenemia) –> could be indicative of the U-shaped curve
- in animal models, when given a more moderate dose, it is shown to benefit, but very high dose showed pre-cancerous lesions
What is hypercarotenemia?
- too much beta-carotene in the blood, which concentrates in the fat levels of the skin
- literally turn orange
- people who take a lot of supplements or drink 1 gallon of carrot juice/day
- an example of the U-shaped curve
Which vitamin is the visual cycle highly dependent on?
Vitamin A - specifically, retinal
What happens to the visual cycle when deficient in vitamin A/retinal?
- visual cycle cannot regenerate as well
- regeneration of rhodopsin is delayed –> until it is reformed, light cannot be perceived
What is the relationship between nightblindness and vitamin A?
1) in dim light, can make out the details of a room
2) a flash of bright light momentarily blinds you as the pigment in the retina is bleached
3) quickly recover and can see the details again in a few seconds
* *when vitamin A deficient, do not recover, but remain blind for many seconds –> this inability to recover = nightblindness
What role does vitamin A play in gene expression?
In transcription factor (vitamin-protein receptor), which initiates gene expression
- when transcription of a gene is turned on, it increases the amount of mRNA made
- if you don’t have the vitamin (a.k.a. ligand) to bind with the protein receptor, then the rest of the gene expression pathway does not work
What role does Vitamin A play in cell differentiation?
1) Aids in barrier functions of epithelial tissue in eyes, intestine, lungs, etc…
- a deficiency leads to an increased risk of infection
- moist & lubricated (mucus) tissue vs. hard & dry (keratin)
2) Immune system
- vitamin A req’d for the differentiation of precursor cells (white blood cells)
What is xerophthalmia?
Dry eyes
- vitamin A deficiency
What does Vitamin A supplementation help prevent?
1) infection
2) blindness
In what instance can Vitamin A be toxic?
Retinol can be toxic at high doses
- can become a teratogen that causes birth defects
What is Vitamin D synthesized from on the skin? How?
formed from cholesterol through sun exposure
cholesterol –> dehyrdrocholesterol – (sun on skin) –> Vitamin D3 (cholecalciterol)
fact check this
Where/when does no synthesis of Vitamin D occur?
during the winter at latitudes greater than 40 degrees north/south
Where do the main functions of Vitamin D lie?
1) Bone health
2) Gene expression
3) Calcium absorption (bone health..?)
What role does Vitamin D play in bone health?
Maintains calcium levels in the blood by…
- increasing calcium absorption in intestine
- increasing reabsorption of calcium from kidneys
- increasing calcium resorption (breakdown) from bone
- stimulating bone formation when calcium is adequate
What role does Vitamin D play in gene expression?
In transcription factor (vitamin-protein receptor), which initiates gene expression
- if you don’t have the vitamin (a.k.a. ligand) to bind with the protein receptor, then the rest of the gene expression pathway does not work
- just like Vitamin A*
What role does Vitamin D play in calcium absorption?
Vitamin D turns on the synthesis of calcium transport proteins
What is rickets?
- result of vitamin D deficiency in children
- loss of mineral component of bone
What is osteomalacia?
- rickets in adults
- loss of mineral component of bone; vitamin D
Who in particular must be supplemented with Vitamin D? Why?
1) babies that are exclusively breastfed (breast milk is low in vitamin D)
2) men & women over 50yrs should take 10ug/400IU daily (biosynthesis of vitamin D in skin declines w. age)
Vitamin D has been linked to reduced risk of _____.
cancer
What are the two main compounds of Vitamin E?
1) Tocopherols
2) Tocotrienols
What is the main form of Vitamin E in the blood?
alpha-tocopherol
- also the main form used in supplements
What are some of the health benefits of Vitamin E?
1) Antioxidant
2) Blood thinner (reduces blood clotting; cardiovascular disease)
Does Vitamin E have a causal relationship with reduced cardiovascular disease?
NO
- linked to prevention of cardiovascular disease in observational studies, but not intervention trials
What is the relationship between vitamins E & C as antioxidants?
the antioxidant function of vitamin E can be restored by another vitamin (such as vitamin C, which gives an electron back to vitamin E)
How does vitamin E work as an antioxidant?
neutralizes free radicals in the cell membrane by donating one of its electrons
What are the two different forms of vitamin K?
1) phylloquinone (plant form) - green leafy vegetables
2) menaquinones (synthesized in supplements)
What are the main functions of Vitamin K?
1) blood clotting - for damaged tissue (i.e. a cut), or if on blood thinning meds, vit K should be taken consistently
2) bone metabolism - vit K is req’d for proteins in bone that regulate bone metabolism
What do fibrin threads do?
form the webbing of a blood clot
