Chapter 8: The Vitamins

The Vitamins
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The Vitamins—An Overview
• Potent, essential, non-kcaloric, and
organic nutrients are needed from foods in
trace amounts to perform specific
functions
– Promote growth, reproduction, and the
maintenance of health and life
• U.S. intakes of vitamins A, D, E, and C
and folate may fall below
recommendations

The Vitamins—An Overview (cont’d.)
• How do vitamins differ from
carbohydrates, fats, and proteins?
– Structure: individual units
– Function: not energy yielding
– Dietary intakes: micro- or milligrams
• Bioavailability
– What is a vitamin’s bioavailability?

• Bioavailability
– Factors affecting the bioavailability of a
vitamin:
• Digestion efficiency and GI tract transit time
• Previous nutrient intake and nutrition status
• Other foods consumed at the same time
• Method of food preparation
• Nutrient source (naturally occurring, synthetic,
fortified)

• Precursors (provitamins)
– Some vitamins consumed as precursors that
must be converted into the active form
– Listed in Tables 8-4 and 8-5
• Organic nature
– Can be destroyed during processing
– Vulnerable to heat, light, and/or oxygen
exposure

• Solubility: two classes
– Water-soluble: B vitamins and vitamin C
– Fat soluble: vitamins A, D, E, and K
– Solubility affects absorption, transport,
storage, and excretion

The Fat-Soluble Vitamins
• Overview
– Vitamins A, D, E, and K
– Usually occur together in fats and oils
– Absorbed in the same manner as lipids
– Stored in the liver and fatty tissues

The Fat-Soluble Vitamins
• Vitamin A and beta-carotene
– How is beta-carotene related to vitamin A?
– Vitamin A’s role in gene expression
• Retinoic acid helps activate or deactivate genes
– Vitamin A’s role in vision
• Maintains cornea
• Rhodopsin (opsin + retinal) participates in light
detection in retina
• Early deficiency causes night blindness

Vitamin A’s Role in Vision

The Fat-Soluble Vitamins:
Vitamin A and Beta-Carotene (cont’d.)
• Vitamin A’s role in protein synthesis and
cell differentiation
– Differentiation: development of specific
functions during cell maturation
• Vitamin A’s role in immunity
– Immune defenses
– Regulation of related genes

• Vitamin A’s role in reproduction, growth,
and development
– Sperm development
– Fetal growth and development
• Beta-carotene’s role as an antioxidant
– Antioxidant: compound that protects other
compounds from oxygen by itself reacting
with oxygen

• Vitamin A deficiency
– All epithelial surfaces: cells harden (produce
keratin) and flatten
– Major cause of preventable blindness
(xerophthalmia) via damage to cornea
• Xerosis (dryness) → keratomalacia (softening)
– Increased susceptibility to infection

• Vitamin A toxicity
– Caused by excessive preformed vitamin A
– Teratogenic risk (birth defects)
– Weakens bones
• Beta-carotene conversion and toxicity
– Retinol activity equivalents (RAE)
– High intake from foods not hazardous
– High intake from supplements may be

• Vitamin A in foods
– Preformed vitamin A: liver, fish oil, milk,
cheese, fortified cereals
• Beta-carotene in foods
– Bright orange produce: carrots, sweet
potatoes, pumpkins, cantaloupe, apricots
– Dark green vegetables: spinach, other
greens, broccoli

Good Sources of Vitamin A and Beta-
Carotenea

The Fat-Soluble Vitamins (cont’d.)
• Vitamin D (calciferol)
– Body can synthesize it with help of sunlight
– Two major forms:
• Vitamin D2 (ergocalciferol): plant foods form
• Vitamin D3 (cholecalciferol): animal foods form;
form synthesized in human skin
– Vitamin D’s metabolic conversions
• Requires conversions by the liver and kidneys

The Fat-Soluble Vitamins: Vitamin D
(cont’d.)
• Vitamin D’s metabolic conversions
– Liver manufactures precursor
– In skin, this compound converted to second
precursor in the presence of ultraviolet rays
– Requires additional conversions by the liver
and then the kidneys to produce active
vitamin
• This step necessary with dietary vitamin D as well

(cont’d.)
• Vitamin D’s potential roles in health
– Why is vitamin D actually a hormone?
– Possible roles under investigation relate to:
• Brain and nerve cells
• Muscle cells
• Immune cells
• Adipose tissue (obesity)
• Diseases such as high blood pressure, type 2
diabetes, and some cancers

(cont’d.)
• Vitamin D’s role in bone growth
– Maintains bone health by assisting in calcium
and phosphorus absorption
– Regulates blood concentrations of bone
minerals:
• Enhances their absorption from GI tract
• Stimulates reabsorption from blood by the kidneys
• Triggers mobilization from bones into blood

(cont’d.)
• Vitamin D deficiency
– Contributing factors: dark skin, breastfeeding
without supplementation, lack of sunlight, and
not consuming fortified milk
– Diseases
• Rickets (in children): weakening of bones
• Osteomalacia: softening of bones
• Osteoporosis: reduced density of bones

(cont’d.)
• Vitamin D toxicity
– Causes excess blood calcium, calcification
• Vitamin D from the sun
– Can pose risk of skin cancer, but not vitamin
D toxicity
– 5 to 10 minutes sun exposure (hands, face,
arm) a few times a week in summer adequate
for most
• Affected by skin color, latitude, season, time of day

(cont’d.)
• Vitamin D in foods
– Eggs, liver, butter, some fatty fish, and fortified
milk
– Supplements for breastfed infants
• Vitamin D recommendations
– DRI assume no skin synthesis
– Why does the RDA for vitamin D increase with
age?

• Vitamin E (alpha-tocopherol)
– Vitamin E as an antioxidant
• Prevents oxidation of polyunsaturated fatty acids
and other lipids
• Protects the lungs
• May reduce LDL oxidation and thus reduce
atherosclerosis

The Fat-Soluble Vitamins: Vitamin E
(cont’d.)
• Vitamin E deficiency
– Erythrocyte hemolysis in premature infants
– Adults
• Loss of muscle coordination and reflexes
• Impaired movement, vision, and speech
• Usually occurs with diseases of the liver,
gallbladder, or pancreas

The Fat-Soluble Vitamins: Vitamin E
(cont’d.)
• Vitamin E toxicity
– Associated with supplement use
– Interferes with blood clotting
• Vitamin E in foods
– Vegetable oils and products made from them
– Wheat germ oil
– Whole grains, fruits, vegetables, nuts

• Vitamin K
– Roles in blood clotting and bone protein
synthesis
– Blood clotting: needed for activation of several
proteins involved in blood clot formation

Blood-Clotting Process

The Fat-Soluble Vitamins: Vitamin K
(cont’d.)
• Intestinal synthesis (by bacteria)
– Insufficient as a sole source
• Vitamin K deficiency
– Fat malabsorption
– Antibiotics or anticoagulants

The Fat-Soluble Vitamins: Vitamin K
(cont’d.)
• Vitamin K nutrition for newborns
– Single dose given a birth
• Vitamin K toxicity
– Rare; no UL established
– High doses interfere with anticoagulants
• Vitamin K in foods
– Green leafy vegetables, cabbage family, some
vegetable oils

The Water-Soluble Vitamins
• Overview
– B vitamins and vitamin C
– Easily absorbed into the bloodstream
– Easily excreted when blood concentrations
rise too high

The Water-Soluble Vitamins (cont’d.)
• The B vitamins
– Coenzymes: small molecules that work with
enzymes to promote their activities
• Help the body use energy-yielding nutrients
• B vitamins are components in coenzymes
• Help cells multiply
• Assist enzymes in performing molecular
conversions

Coenzyme Action

The Water-Soluble Vitamins:
The B Vitamins (cont’d.)
• B vitamin deficiencies
– Thiamin ► beriberi
– Niacin deficiency ► pellagra
• Interdependent systems
• B vitamin enrichment of foods
– How do fortification and enrichment protect
people against deficiencies?

• Thiamin
– Critical role in energy metabolism in all cells
– Necessary for normal nerve and muscle
functioning
– Thiamin deficiency and toxicity
• Who is most likely to develop a thiamin deficiency?
– Food sources
• Pork, whole grain or enriched bread and cereals;
small amounts in nearly all nutritious foods

• Riboflavin
– Serves as a coenzyme in energy metabolism
– Riboflavin deficiency and toxicity
• Deficiency causes cracks at corners of mouth and
sore throat
– Riboflavin in foods
• Milk and milk products, enriched grain products,
green vegetables, meats
– Effects of light
• Light sensitive, but heat stable

• Niacin
– Coenzyme in energy metabolism in all cells
– Body can produce niacin from tryptophan
• Niacin equivalents (NE)
– UL (prevents “niacin flush”): 35 mg NE
– Niacin (nicotinic acid) used as a medication
• Large (pharmacological) doses lower blood
cholesterol
• Used in atherosclerosis treatment

• Niacin
– Niacin in foods: meat, poultry, fish, legumes,
enriched and whole grains
• Pantothenic acid and biotin
– Important in energy metabolism
– Pantothenic acid and biotin in foods:
widespread
– Biotin deficiency: intravenous feeding, avidin

• Vitamin B6
– Metabolic roles of vitamin B6
• Macronutrient metabolism
• Conversion of amino acids to other, nonessential
amino acids
• Synthesis of hemoglobin and neurotransmitters
• Release of stored glucose from glycogen

• Vitamin B6
– Vitamin B6 deficiency
• Symptoms: weakness, depression, confusion,
irritability, dermatitis, anemia, convulsions
– Vitamin B6 toxicity
• Results from supplement use (2 g/day)
• Recovery after discontinuing supplements

• Vitamin B6
– Vitamin B6 recommendations
• RDA based on amounts needed to maintain
adequate coenzyme levels
– Vitamin B6 in foods
• Protein-rich meat, fish, poultry, potatoes
• Heat sensitive

• Folate
– Active in cell division
– Folate, alcohol, and drugs: negative impact on
folate status
• Alcohol: impairs absorption, increases excretion
• Medications: aspirin, oral contraceptives, and
anticonvulsants
• Smoking

• Folate
– Folate and neural tube defects (NTD)
• Prevented by supplements in early pregnancy
• UL: 1000 µg/day from fortified foods and
supplements
– Folate in foods
• Liver, legumes, beets, and leafy green vegetables
• Dietary folate equivalents (DFE) (Box 8-1)

Good Sources of Folatea

• Vitamin B12
– Vitamin B12, folate, and cell division
• Accepts carbon groups from folate, regenerating
folate’s active form
• Macrocytic anemia
– Vitamin B12 and the nervous system
• Maintains nerve fibers
• What dangers are associated with folate
supplementation masking a vitamin B12 deficiency?

• Vitamin B12
– Vitamin B12 absorption
• Requires intrinsic factor
• Atrophic gastritis and pernicious anemia
– Vitamin B12 in foods
• Found almost exclusively in animal-derived foods
• Fortified foods (e.g., soy milk), supplements
– Vitamin B12 deficiency in vegans

• Non-B vitamins
– Serve as coenzymes in metabolism
– Inositol, choline, and carnitine
• Choline assigned AI
– Other non-B vitamins
• Para-aminobenzoic acid (PABA), bioflavonoids
(vitamin P or hesperidin), and ubiquinone

• Vitamin C
– Antiscurvy factor: ascorbic acid
– Metabolic roles of vitamin C
– Vitamin C’s role in collagen formation
– Vitamin C as an antioxidant
– Vitamin C in amino acid metabolism
– Role of stress
– Vitamin C as a possible antihistamine

Vitamin C (cont’d.)
• Vitamin C’s role in cancer prevention and
treatment
• Vitamin C deficiency
– Affect on blood vessels: bleeding gums and
pinpoint hemorrhages
– What are symptoms of scurvy?

• Vitamin C toxicity
– GI symptoms, food-drug interactions, false
urine test results
– Increased kidney stone risk with gout or
genetic abnormality in vitamin C metabolism
• Recommended intakes of vitamin C
– RDA for men: 90 mg
– RDA for women: 75 mg

• Special needs for vitamin C
– Infections, burns, surgery, extremely high or
low temperatures, toxic doses of heavy
metals, chronic medication use
– Smokers: recommendation of 125 mg/day for
men and 110 mg/day for women
• Safe limits
– 100 to 300 mg per day

• Vitamin C in foods
– Many fruits and vegetables
• Vitamin C and iron absorption
– How does vitamin C impact iron absorption?

Good Sources of Vitamin Ca

Nutrition in Practice:
Phytochemicals and Functional Foods
• Phytochemicals: bioactive plant
compounds
– Flavonoids
– Carotenoids (beta-carotene, lycopene)
– Compounds in soy foods, flaxseed
• Functional foods
– Are manufactured variety foods or drugs?
– Potential benefits and disadvantages

Chapter 8: The Vitamins

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