Lecture 6: Vitamins Flashcards
What are vitamins?
Tasteless, organic compounds
Required in small amount
What are the functions of vitamins?
- Regulate metabolism
- Help convert energy in fat, carbohydrate, and protein into ATP
- Promote growth and reproduction
History of vitamins
- Mostly undiscovered until about a century ago
- Scientists discovered that thiamin cured beriberi and vitamin D cured rickets
- Scientists focus on disease prevention with vitamin research
- Each new vitamin is temporarily names when discovered
What is the criteria for designating vitamins?
- Cannot be synthesized in ample amounts in the body
- Chronic deficiency is likely to cause physical symptoms.
- Symptoms will usually disappear once the vitamin level in the body is restored.
~Deficiency can cause permanent damage.
How are vitamins classified?
Based on solubility
How many water-soluble vitamins are there?
Nine: Entire B vitamin complex + vitamin C
How many fat-soluble vitamins are there?
Four:
~Vitamin A
~Vitamin D
~Vitamin E
~Vitamin K
What does vitamin solubility influence?
- Digestion
- Absorption
- Transportation
- Storage
- Excretion
Vitamin Structure
All contain: Carbon, hydrogen and oxygen
Some contain: nitrogen and sulfur
The chemical structure of each vitamin is unique.
How are vitamins absorbed?
They are absorbed intact
Functions of vitamins
They perform essential functions and some vitamins perform multiple.
- Antioxidants
- Blood clotting and red blood cell synthesis
- Bone health
- Energy Production
- Growth and reproduction
- Immune function
- Protein metabolism and synthesis
What are provitamins?
Substances found in foods that are not directly usable by the body
- Can be converted into active form once absorbed
~beta-carotene –> vitamin A
What is the difference between preformed vitamins and provitamins?
Preformed vitamins are found in food in their active form and not need to be converted
Provitamins are found in food and need to be converted to active form
How can vitamin toxicity (hypervitaminosis) occur?
- Rarely occurs
- Results from ingesting excess vitamins leading to tissue saturation
- Can damage cells
- Results from high doses of supplements; cannot occur from foods
- More likely to occur with fat-soluble vitamins
The DRI includes an UL for most vitamins to prevent excess
Where does vitamin absorption take place?
All absorption takes place in small intestine
How do fat-soluble and water-soluble vitamins differ?
They differ in:
~Absorption
~Bioavailability
What does bioavailability depend on?
Based on:
- Amount of food
- Preparation
- Efficiency of digestion and absorption of food
- Individual nutritional status
- Natural or synthetic
Which vitamins are more bioavailable?
Water-soluble are more bioavailable than fat-soluble
Animal food vitamins are more bioavailable than plant food vitamins
Absorption of Fat-soluble vitamins
- Attached to proteins in foods and released in stomach
- Absorbed in duodenum
- Packaged in chylomicrons –> travel through lymph system
–> into bloodstream
Storage of Fat-soluble vitamins
- The liver is the main storage site for vitamin A; to a lesser
extent for vitamins K and E. - Vitamin D is mainly stored in the fat and muscle tissue.
- Can build up in the body to the point of toxicity
Absorption of Water-soluble vitamins
- Absorbed with water and enter directly into the bloodstream
- Most absorbed in the duodenum and jejunum
Excretion of Water-soluble vitamins
- Excess intake excreted through the
urine - Important to consume adequate
amounts daily - Dietary excesses can be harmful
Best sources of vitamins
Whole foods:
~ Fruits, vegetables, and whole grains
~Rich in vitamins, phytochemicals, antioxidants, and fiber
Fortification of food with vitamins
Fortified foods: Voluntary addition of nutrients by manufacturers to:
~Enhance the nutrient quality of food
~Prevent or correct dietary deficiencies
~Ensure adequate intake for some individuals
~Examples: vitamin D in milk, vitamin D and
calcium in juice, iodine in salt
- Enrichment is a form of fortification.
~Example: folic acid in refined flour
- Fortification can contribute to health risks.
~Lead to vitamin excess
~Displace nutrient-rich foods
What affects vitamin activity?
Exposure to:
~UV light
~water
~pH changes
~heat
~air
- time since harvest
- storage conditions
- cooking methods
Primary Functions of Fat-Soluble Vitamins
- Antioxidant: Vitamins A (carotenoids) and E
- Vision: Vitamin A
- Gene expression: Vitamins A and D
- Calcium balance: Vitamin D
- Bone health: Vitamins D and K
- Immune function: Vitamins A and D
Primary Functions of Water-Soluble Vitamins
- Antioxidant: Vitamin C
- Nerve function: Thiamin
- Protein synthesis: Niacin
- Formation of red blood cells: Folate and vitamin B12
- Several B vitamins function as coenzymes and have critical roles in metabolism
What are antioxidants?
Group of compounds that neutralize free radicals, helping
to counteract the oxidation that takes place in cells
- Includes:
~Vitamin E
~Vitamin C
~Selenium
~Flavonoids
~Carotenoids
- Antioxidant-rich foods also contain other protective compounds.
- Antioxidant-rich foods and may reduce the risk of some cancers.
- Antioxidants and phytochemicals from the diet have more health benefits than those from supplements.
What are free radicals?
By-products of the body’s metabolic reactions
They are molecules with an unpaired electron, which makes them unstable
What is oxidative stress?
Occurs when free radicals accumulate faster than the body
can metabolize them.
What are the effects of oxidative stress?
- Damages DNA and body proteins, and alters cell structure
- Excess free radicals and not enough antioxidants may contribute to chronic diseases
~Heart disease
~Cancer
~Aging
~Cataracts
~Age-related macular degeneration
~Diabetes
~Parkinson’s Disease
~Alzheimer’s Disease
Are vitamin supplements necessary?
NO
- No evidence supports the use of supplements and preventing chronic diseases or cognitive decline.
- Not a substitute for healthy eating
- Can cause adverse side effects
Vitamin supplement regulation
Are not regulated like drugs and do not require FDA approval to be put on the market
~Supplements can’t be removed unless they have been shown to be unsafe or cause harm.
How to choose a vitamin supplement?
Choose supplements with independent verification
~Example: United States Pharmacopeial Convention seal (USP)
Who can vitamin supplements be helpful for?
- Pregnant and lactating women
- Older individuals who need vitamin B12
- Individuals who lack dietary vitamin D or sun exposure
- Individuals on low-kilocalorie diets
- Strict vegetarians
- Individuals with food allergies or lactose intolerance
- Individuals who abuse alcohol
- Individuals who are food insecure
- Breast-fed infants
Which compounds can reduce cancer risk?
- Phytonutrients (lycopene)
- Antioxidants (carotenoids, selenium, vitamin C, vitamin E)
- Retinoids (vitamin A)
- Vitamin D
- Folate
- Omega-3 fatty acids
- Fiber
