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Questions and Answers

What defines a free radical?

An unstable molecule with one or more unpaired electrons (correct)

A nutrient that supports cellular health

A harmless molecule found in the body

A stable molecule with paired electrons

Which of the following is a source of free radicals aside from normal body processes?

Consuming antioxidants

Sleeping

Hydrating adequately

Sunlight exposure and UV radiation (correct)

What role do antioxidants play in relation to free radicals?

Donating an electron to neutralize them (correct)

Transforming free radicals into nutrients

Increasing the stability of free radicals

Creating more free radicals

Which vitamin is specifically noted for stopping free radical chain reactions in lipids?

Vitamin E Signup and view all the answers

What is a major consequence of oxidative damage to cellular DNA?

Development of cancer Signup and view all the answers

Which of the following statements about vitamin C is true?

It protects LDL from oxidation and may help lower cholesterol. Signup and view all the answers

What is the current understanding of selenium's role in heart disease?

More research is needed on its effects. Signup and view all the answers

Which statement about vitamin E supplementation is accurate?

High doses may lead to adverse effects. Signup and view all the answers

Which vitamin is considered the most active form of vitamin A?

Retinol Signup and view all the answers

What is the primary method by which vitamin A is transported from the liver to cells?

Retinol-Binding Protein (RBP) Signup and view all the answers

Which of the following food sources is NOT rich in retinoids?

Carrots Signup and view all the answers

What role does retinoic acid play in tumor cells?

Inhibits cell growth Signup and view all the answers

Which vitamin acts as an antioxidant by donating electrons to free radicals?

Vitamin C Signup and view all the answers

What is the primary role of rhodopsin in vision?

To convert light energy into nerve impulses Signup and view all the answers

Which process is involved in the regeneration of rhodopsin after it is activated?

CIS to TRANS configuration shift of retinal Signup and view all the answers

How does Vitamin A contribute to cell differentiation?

By regulating protein synthesis for specific functions Signup and view all the answers

In what way does Vitamin A support reproductive health in males?

By assisting in sperm development Signup and view all the answers

Which of the following roles of Vitamin A involves bone health?

It assists in breaking down bone to facilitate growth Signup and view all the answers

What characterizes fat soluble vitamins?

They require bile for absorption. Signup and view all the answers

How do antioxidants function in relation to free radicals?

They prevent the formation of free radicals by donating electrons. Signup and view all the answers

What is a primary characteristic of water soluble vitamins?

They are easily absorbed and excess is excreted through urine. Signup and view all the answers

Which vitamins are considered fat soluble?

Vitamins A, D, E, K Signup and view all the answers

What leads to oxidative stress in the body?

A deficit of antioxidants. Signup and view all the answers

What compounds act as antioxidants along with beta-carotene?

Vitamin C, E, and Selenium Signup and view all the answers

Which protein is essential for the transport of vitamin A in the body?

Retinol-binding protein (RBP) Signup and view all the answers

What is a common first sign of vitamin A deficiency?

Night Blindness Signup and view all the answers

What can severe vitamin A deficiency lead to if not addressed promptly?

Xerophthalmia and Total Loss of Vision Signup and view all the answers

How does vitamin A deficiency affect children with measles?

Reduces risk of death by 50% with supplementation Signup and view all the answers

In vitamin A deficiency, what does xerosis lead to?

Decreased mucous production and dryness of the cornea Signup and view all the answers

Which of the following is NOT a factor influencing vitamin A status?

Age of the individual Signup and view all the answers

What is the recommended intervention for treating vitamin A deficiency related to xerophthalmia?

Vitamin A supplementation Signup and view all the answers

What complication is primarily associated with Vitamin A deficiency?

Keratinization Signup and view all the answers

Which population is at the highest risk for Vitamin A toxicity?

Children consuming high doses of supplements Signup and view all the answers

What is the Recommended Dietary Allowance (RDA) of Vitamin A for adult women?

700 ug RAE/day Signup and view all the answers

Which food source is richest in carotenoids?

Dark leafy greens and orange fruits Signup and view all the answers

What vitamin is associated with preventing scurvy?

Vitamin C Signup and view all the answers

Which of the following is a symptom of acute Vitamin A toxicity?

Nausea and vomiting Signup and view all the answers

Which of the following is true about Vitamin E's role as an antioxidant?

It prevents free radical chain reactions Signup and view all the answers

What is the tolerable upper intake level (UL) for adults regarding preformed Vitamin A?

3000 ug/day Signup and view all the answers

Which of the following is a common symptom of Vitamin C deficiency?

Bleeding gums Signup and view all the answers

For which of the following conditions could Vitamin E supplementation pose a risk?

Blood clotting disorders Signup and view all the answers

What is the primary function of Vitamin C as a cofactor?

Collagen formation Signup and view all the answers

Which of the following foods is a poor source of Vitamin C?

White bread Signup and view all the answers

What condition is associated with selenium deficiency?

Keshan Disease Signup and view all the answers

What is the primary function of selenium in the body?

Thyroid hormone activation Signup and view all the answers

Study Notes

Vitamins

Considered micronutrients
Organic compounds vital to life
Indispensable for body functions
Needed in small amounts
Non-caloric essential nutrients
Can be Fat or Water soluble
Precursors/Provitamins are compounds in food converted to active vitamins

Fat Soluble Vitamins

Vitamins A, D, E, K
Absorbed into the lymph, transported in blood with protein carriers
Dissolve in lipids
Require bile for absorption
Stored in the liver and body tissues
Can be toxic in excess from supplements (A, D, K)
Deficiencies occur with low intake or fat malabsorption

Water Soluble Vitamins

B vitamins and vitamin C
Dissolve in water; cooking or washing with water can leach them from foods
Easily absorbed into the bloodstream; excesses excreted in the urine
Not stored extensively in body tissues
Seldom reach toxic levels (high doses in supplements can result in expensive urine)

Antioxidants

Oxidation

Part of normal metabolism
Occurs when atoms lose electrons
As molecules break down, they reform new bonds to make new stable compounds
If an atom has an unpaired electron, it becomes highly unstable and reactive.

Free Radicals

Have unpaired electrons in their outer orbital = unstable
Can damage cells and their functions
Accumulation leads to oxidative stress

What Nutrients are Antioxidants?

Fat Soluble Vitamins: vitamin A (including beta-carotene), vitamin E
Water Soluble Vitamin: vitamin C
Trace Mineral: Selenium

Role of Antioxidants

Protect cells from oxidative damage
Vitamin antioxidants (A, C, E) donate electrons to free radicals to prevent cell damage
Trace mineral antioxidants (Se) are cofactors of enzyme systems that have protective effects
Prevent the creation of new free radicals

Vitamin A & Beta-Carotene

Three active forms in the body:
- Retinol (alcohol form) - most active form
- Retinal (aldehyde form)
- Retinoic acid (acid form)
Retinol converted by cells from retinol
Plant-derived precursor: Beta-carotene

Food Sources

Animal Foods

Contain retinoids (retinol, retinal, retinoic acid)
Provided as retinyl esters—easily digested and absorbed as retinol in the small intestine (SI)

Plant-Based Foods

Provide carotenoids
Beta-carotene can be converted to vitamin A in the small intestine (SI) and liver
Conversion and absorption rates are much lower than from retinoids
Deep orange fruits and dark green leafy vegetables are good sources. (e.g. sweet potatoes, carrots, spinach, bok choy, broccoli, apricots, mango, cantaloupe)

Digestion/Absorption/Transportation

Digested and absorbed by several proteins
Absorbed via the lymph system
Stored in the liver
Retinol-Binding Protein (RBP) picks up vitamin A from the liver and transports it to cells
Cells have RBP receptors
Actions within cells vary depending on the receptor
Retinoic acid stimulates cell growth in skin, inhibits cell growth in tumors

Roles of Vitamin A

1. Vision

Maintains a clear outer window (cornea)
Conversion of light energy to nerve impulses at the retina
Some photosensitive cells in the retina contain rhodopsin (pigment)
Rhodopsin = protein Opsin + retinal

2. Protein Synthesis & Cell Differentiation

Each cell develops to perform a specific function
Goblet cells synthesize and secrete mucous
Maintains integrity of epithelial tissues (e.g., skin, inner mucous membranes lining the GI tract, lungs, eyelids)
Protects from damage of microorganisms and substances including gastric juices

3. Reproduction & Growth

Retinol and sperm development (males)
Fetal development
Children lacking vitamin A have poor growth
Bone remodeling necessary for bone growth
Vitamin A participates in dismantling parts that are not needed (osteoclasts) and builds new parts (osteoblasts)

4. Antioxidant

Beta-carotene is a precursor for vitamin A
Acts as an antioxidant with Vitamin C, E, and Selenium

Vitamin A Deficiency – Hypovitaminosis A

Vitamin A status depends on:
- Adequacy of vitamin A stores
- Protein status
Retinol-binding protein (RBP) is the vitamin's carrier within the body
Deficiency occurs when intake is inadequate and stores are depleted
Symptoms develop slowly in healthy adults, faster in growing children
Common problem in developing countries
Prevented through food fortification or supplementation

Complications of Vitamin A Deficiency

Infectious Diseases

Inhibits measles virus replication
Severity of illness in developing countries correlates with degree of vitamin A deficiency
Providing vitamin A to children with measles can reduce death risk by 50%
Two doses of vitamin A supplement 24 hours apart recommended for all children with measles.

Night Blindness

One of first signs of vitamin A deficiency
Retina doesn't receive enough retinal to regenerate pigments
Limited ability to see after a flash of light or after dark
Corrected with vitamin A supplementation

Blindness (Xerophthalmia)

Total loss of vision
Lack of vitamin A at the front of the eye (cornea)
Severe vitamin A deficiency is a leading, preventable cause
Develops in stages: Xerosis (dry and hard cornea); Keratomalacia (softening of the cornea); Irreversible blindness

Keratinization

Skin becomes dry, rough, scaly as keratin accumulates
Keratin is a hard, inflexible protein found in hair and nails

Gastrointestinal Tract

Decreased number and activity of goblet cells
Decreased digestion and absorption of nutrients

Vitamin A Toxicity – Hypervitaminosis A

Symptoms develop when all binding proteins are loaded
Excess vitamin A is free to damage cells
Not likely when diet is balanced
Children at higher risk
Beta-carotene from food is not as likely to cause toxicity
Not efficiently converted into vitamin A; stored in fat under the skin
Supplements can be harmful and act as pro-oxidants

Vitamin A Toxicity

Bone Defects

Chronic excess intake may contribute to osteoporosis

Birth Defects

Spina bifida and cleft palate
Excess supplementation before the seventh week of pregnancy is most harmful and is usually not given in the first trimester.

Acne

Large doses do not have an impact on acne

Acute Toxicity Symptoms

Nausea, vomiting, blurred vision, headaches, lack of muscle coordination.

Vitamin A Recommendations

RDA:
- Women: 700 ug RAE/day
- Men: 900 ug RAE/day
- Expressed as retinol activity equivalents (RAE).
- 1 IU retinol = 0.3 ug retinol or 0.3 ug RAE
UL for adults: 3000 ug
- Applies to preformed vitamin A

Vitamin A in Foods

Foods from animals contain retinoids (liver, fish oils, milk, butter, eggs). Fortified milk (low %MF)
Plant-based foods contain carotenoids (precursors for Vitamin A). (e.g. deep orange fruits and dark green leafy vegetables)
Bioavailability depends on the fat content of the meal.

Vitamin A in Foods: Color of the food

Dark, leafy green and deep yellow-orange fruits and vegetables contain: highest amounts of vitamin A. (e.g., squash, canteloupe, carrots - not corn or bananas)
Spinach is not a good source.
Chlorophyll is the green pigment that absorbs and transfers light energy to initiate photosynthesis.
Beets and corn have lower levels of vitamin A despite the bright colour because they derive this colour from xanthophyll.

Vitamin E: Role as an Antioxidant

Defends body against oxidative damage from free radicals
Prevents chain reactions leading to production of more free radicals
Protects vulnerable components of cells, including the membranes from destruction
Prevents oxidation of polyunsaturated fatty acids (PUFAs)
May reduce risk of heart disease
Preventing oxidation of LDL (low-density lipoprotein)
Reducing inflammation.

Vitamin E Deficiency

Primary deficiency from poor dietary intake is rare. It can occur if people consume diets very low in fat, or a lot of highly processed foods
Deficiency associated with diseases affecting fat absorption (e.g., cystic fibrosis), or liver, gallbladder or pancreas disorders
Deficiency results in erythrocyte hemolysis (RBC rupture) causing spilling of contents, and anemia because it is related to oxidation of PUFAs in the cell membrane
Seen in premature infants before transfer of vitamin E from mother
Corrected with vitamin treatment

Vitamin E Toxicity

Increased use of vitamin E supplements over recent years due to recognition of protective properties against chronic disease.
Toxicity is rare
Interaction with vitamin K
At extremely high doses, vitamin E can enhance effects of drugs used to prevent blood clotting (anticoagulants).
May result in hemorrhage
Ongoing research needed linking increased risk of hemorrhagic stroke.

Vitamin E Recommendations & Food Sources

RDA: 15mg/day for adults
UL: 1000mg/day for adults
Food Sources: vegetable oils, foods made from vegetable oils. Seeds and nuts. Limited amount in processed foods.

Vitamin C: Other term - Ascorbic acid

Scurvy

Vitamin C deficiency was prevalent among sailors on long voyages
Fruits and vegetables are often used up within the first few days
Nutrition experiment in the 1700s revealed that citrus juice quickly resolved scurvy and then became a standard practice.

Roles of Vitamin C

Antioxidant in body cells and fluids

Loses electrons easily, neutralizes free radicals and can take electrons back to become active again
Enhances iron (Fe) absorption and protects it from oxidation

Cofactor in collagen formation

Helps form collagen which is essential for:
- Bone and teeth formation
- Cell formation
- Scar formation

Cofactor in other reactions

Helps in the hydroxylation of carnitine
Participates in the conversion of tryptophan to serotonin and tyrosine into norepinephrine
Assist in the production of hormones, including thyroxine (regulates BMR)

Stress

Increasing vitamin C needs; burns, extreme temperatures, infections, some medications, smoking
Adrenal glands release vitamin C and hormones during stress.

The Common Cold

Research is conflicting; taking large amounts of Vitamin C may decrease duration and likelihood
Can deactivate histamine

Vitamin C Recommendations

RDA:
- Men: 90 mg/day
- Women: 75 mg/day
- 10 mg/day to prevent scurvy
- ~100 mg/day—provides tissue saturation
- ~200mg/day—max absorption; any additional is excreted
- Increased needs for smokers (~135 mg/day)
UL: 2000mg/day

Vitamin C Deficiency

Scurvy
Mouth: bleeding gums, loosened teeth, microcytic anemia.
Bone fragility, joint pain
Atherosclerotic plaques
Immunity: increased infections, poor wound healing
Muscle: degeneration, pain
Skin: rough, blotchy, bruising easily, and pinpoint hemorrhages.

Vitamin C Toxicity

GI upset (excessive supplementation)
Excess vitamin C in urine can interfere with some medical tests (e.g., diabetes diagnosis)
Increased supplement use may counteract some medications (e.g., blood clotting).
Kidney disease—may increase risk of kidney stone formation
Adverse effects associated with iron overload.

Food Sources of Vitamin C

Citrus fruits
Cabbage-type vegetables
Dark green vegetables
Berries
Tomatoes
Bell peppers
Mango, papaya

Selenium

Roles of Selenium

Antioxidant: Works with vitamin E as part of proteins (enzyme glutathione peroxidase) to prevent free-radical formation
As part of other enzymes that activate or deactivate thyroid hormone (role in BMR).

Selenium Deficiency

Not very common
Associated with Keshan disease (a type of heart disease)
Prevalent in parts of China where soil and food lack selenium.
Prevented by adequate selenium intake

Selenium Recommendations & Sources

RDA: 55 ug/day for adults
UL: 400 ug/day for adults
Food sources:
- Meat, milk and eggs
- Fruit, vegetables, and grains (levels depend on soil they were grown in).

Selenium Toxicity

High doses can be toxic (loss and brittleness of hair and nails, garlic breath odor, nervous system abnormalities, fatigue, irritability).

Free Radicals & Disease

Free radical is an unstable molecule with one or more unpaired electrons, highly reactive.
Steals an electron from another molecule, that molecule becomes unstable and a free radical.
Free radicals come from UV radiation, air pollution, and tobacco smoke in addition to normal body processes.
Antioxidants donate an electron to neutralize free radicals and do not become free radicals.

Defending Against Free Radicals

System of enzymes disarms harmful oxidants. This is dependent on levels of selenium, copper, manganese, iron, and zinc.
Inadequate dietary intake = weakened defense.
Antioxidant vitamins:
- Vitamin E defends body lipids from free radical chain reaction
- Beta-carotene acts in lipid membranes
- Vitamin C protects the skin, blood and restores oxidized vitamin E to its active state.

Defending Against Cancer

Cancer results from damage to cellular DNA
Antioxidants may protect DNA from oxidative damage.
Research has linked certain antioxidants with different types of cancers.
Research supports a diet rich in fruits and vegetables containing antioxidants to benefit cancer prevention.

Defending Against Heart Disease

Vitamin E may protect against HTN and CVD; defend against LDL oxidation, inflammation, arterial injuries, blood clotting - Caution with high supplemental doses of Vitamin E as it can lead to adverse effects
Vitamin C protects against LDL oxidation, raises HDL levels, lowers total cholesterol and improves BP. Role of vitamin C supplementation in prevention of heart disease remains uncertain.
Selenium – further research is needed to determine the role of selenium and heart disease.

Foods vs Supplements

Discussion of using food sources rather than supplements for antioxidant nutrients in relation to chronic disease

Mid-Term #2

Dates, Times, Duration, and Format for the upcoming mid-term exam.

Library Session

Asynchronous online session available for review
Materials will be posted by Tuesday November 12, 2024
A quiz is available on Thursday November 14th, 2024 until Thursday November 21st, 2024 at 11:59pm.

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