Ch 6 ppt

CHAPTER 6

Vitamins

Eleanor D. Schlenker

Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc.

2 Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc.

Vitamins

Criteria used to define a compound as a

vitamin:

It must be an organic dietary substance that is not

an energy-producing carbohydrate, fat, or protein

It is needed in very small quantities to perform a

particular metabolic function or prevent an

associated deficiency disease

It cannot be manufactured by the body and

therefore must be supplied in food


Vitamins: Basic Concepts

As our understanding of vitamins has

expanded, the following important concepts

have emerged:

Individual vitamins are multifunctional

One vitamin cannot substitute for another vitamin

Vitamins work together in carrying out body

functions

Vitamins function best when all are present in the

appropriate proportions


Classification of Vitamins

Vitamins have been grouped according to

their solubility in either fat or water

Fat-soluble vitamins

• A, D, E, and K

• Closely associated with body lipids and are easily stored

Water-soluble vitamins

• Vitamin C and the B-complex family

• Easily absorbed and transported

• Cannot be stored except in the general sense of tissue

saturation


Fat-Soluble Vitamins

Vitamin A

Generic name for a group of compounds

having similar biologic activity: retinol, retinal,

and retinoic acid


Fat-Soluble Vitamins – Cont’d

There are two dietary forms of vitamin A:

1. Preformed vitamin A (retinol)

• Natural form of vitamin A found only in animal foods and

usually associated with fat

2. Provitamin A (beta-carotene)

• Plants cannot synthesize vitamin A but instead produce a

family of compounds called carotenoids

• Beta-carotene, converted to vitamin A in the body,

provides about 21% of the total vitamin A intake in the

United States

• Poor conversion of carotenoids to vitamin A may

contribute to vitamin A deficiency in developing countries

where persons depend on plant sources


Absorption of Vitamin A

Various materials are needed for the

absorption of vitamin A or beta-carotene:

Bile salts

Pancreatic lipase

Dietary fat


Conversion of Beta-Carotene

Beta-carotene can be absorbed and used by

the body in its original form or be converted to

vitamin A

Carotenoids are important both as vitamin A

precursors and as phytochemicals


Transport and Storage of Vitamin

A

The route of absorption of both vitamin A and

the carotenoids parallels that of fat

The liver contains up to 85% of the body’s

total supply of Vitamin A

A prophylactic dose of vitamin A every 6

months prevents deficiency in developing

countries


Functions of Vitamin A

Visual adaptation to light and darkness

Generalized actions that affect the integrity of:

Body coverings and linings (epithelial tissues)

Growth

Immune response

Reproductive function


Vitamin A Deficiency

Vision Normal rhodopsin cannot be made and the rods

and cones of the retina become increasingly sensitive to changes in light, causing night blindness

Reversed with retinol injection


Vitamin A Deficiency – Cont’d

Cell differentiation Keratinization: dry and flat cells

• Eye—xerophthalmia and blindness

• Respiratory tract—dryness and loss of cilia

• Gastrointestinal tract—dryness, poor digestion, and absorption

• Skin—dry and scaly, follicular hyperkeratosis

• Tooth formation—ameloblasts do not develop


Vitamin A Deficiency – Cont’d

Growth Essential for growth of bones and soft tissues

Controls protein synthesis and mitosis

Excessive intakes also cause poor bone health

Reproduction Normal sexual maturation and function

Gene expression and fetal development

Immunity Lack of epithelial and mucosal barrier

Direct effect on cell-mediated and antibody-mediated immunity


Vitamin A Requirement

Influencing Factors

A number of variables can modify the vitamin

A needs of a given individual:

Liver stores

Intake of preformed versus provitamin A

Illness and infection

Gastrointestinal or hepatic defects


Vitamin A Requirement – Cont’d

Causes of Vitamin A Deficiency

Inadequate dietary intake

Poor food selection and fast food

Poor absorption or metabolism

Lack of bile or dietary fat

Inadequate conversion of beta-carotene

Liver or intestinal disease

High intake of alcohol


Vitamin A Requirement – Cont’d

Recommended Dietary Allowance (RDA)

For vitamin A the RDA is the amount required

to maintain optimum liver stores

The RDA for men ages 19 and over is set at 900 µg

The RDA for women of this age is 700 µg

The RDA increases to 770 µg in pregnancy and

1300 µg in lactation


Vitamin A Toxicity

Hypervitaminosis A

High-potency supplements

UL is 3000 µg/day

Especially dangerous in pregnancy


Food Sources of Vitamin A

Animal sources:

Liver, milk, cheese, butter, egg yolk, and fish

Nonanimal products:

Margarine, ready-to-eat cereals, and cereal bars

are being fortified with vitamin A

Deep yellow, orange, red, and dark green

vegetables and fruits, contain carotenoid

precursors of vitamin A

Carotenoids are more available from cooked

vegetables



Vitamin D

A prohormone and in its active form functions as

a hormone

Chemically, vitamin D is a sterol and its

precursor found in human skin is the lipid

molecule 7-dehydrocholesterol



Vitamin D – Cont’d

Two forms:

1. Ergocalciferol (vitamin D2)

• Formed by irradiating ergosterol found in ergot (a

fungus growing on rye and other cereal grains) and

yeast

2. Cholecalciferol (vitamin D3)

• Formed by the action of ultraviolet light from the sun on

the 7-dehydrocholesterol in the skin

• Found naturally in fish liver oils


Vitamin D

Absorption

Absorbed in the small intestine along with fat

Malabsorption diseases, such as celiac

disease, cystic fibrosis, and Crohn’s disease

or pancreatic insufficiency, hinder vitamin D

absorption


Vitamin D – Cont’d

Active Hormone Synthesis

1,25-dihydroxycholecalciferol [1,25(OH)2D3]

has the chemical name of calcitriol

Calcitriol is produced by the combined action of

the skin, liver, and kidneys, an overall process

referred to as the vitamin D endocrine system

Vitamin D3 is used and metabolized in the same

way whether obtained from skin synthesis or from

food


Functions of Vitamin D Hormone

Associated with calcium and phosphorus

metabolism and their absorption and

deposition in bone tissue

Acts on many tissues and functions

throughout the body

Cell growth

Muscle strength

Immune function

Insulin levels

Hypertension and cardiovascular disease


Vitamin D Deficiency

Bone Disease

Without sufficient vitamin D, the body cannot absorb the calcium needed to build normal bones

Children develop rickets

Adults develop osteomalacia

Osteoporosis has different causes

Breastfed infants need vitamin D supplements

Role in renal osteodystrophy


Vitamin D Requirements

Dietary Reference Intake

Needs are affected by sun exposure and skin

synthesis

Vitamin D has an Adequate Intake (AI), not

an RDA

Persons between 6 months and 50 years of

age need 5 µg (200 IU)


Vitamin D Requirements – Cont’d

Dietary Reference Intake – Cont’d

For persons 51 to 70 years, the AI increases

to 10 µg (400 IU)

For those ages 71 and older, it increases to

15 µg (600 IU)

The elevated AI for those over age 70 points to

their critical need to maintain bone mass and their

limited ability to synthesize vitamin D in their skin


Food Sources of Vitamin D

Fatty fish such as mackerel

A small amount occurs in egg yolk

Vitamin D-fortified milk, margarine, juices,

and ready-to-eat cereals

Vitamin D2 is found only in yeast

Vitamin D3 is found mostly in fish liver oils

and is the form added to fortified foods



Vitamin E

Vitamin E is the generic name given to a

group of compounds with similar physiologic

activity

Includes eight fat-soluble, 6-hydroxychroman

compounds having some degree of the biologic

activity of alpha-tocopherol



Absorption

Absorbed in the micelles with the aid of bile

Stored in the liver and adipose tissue, where

it is held in bulk liquid droplets


Functions of Vitamin E

Acts as an antioxidant in destroying

molecules called free radicals

Free radicals are elements or molecules with

unpaired electrons that attack double bonds

in membranes and other body tissues


Functions of Vitamin E – Cont’d

Changes caused by the “oxidation” of these

double bonds affects the function of these

membranes and tissues

Partners with selenium

Unproven role in preventing chronic disease

and aging changes in tissues

May ameliorate toxicity associated with

chemotherapy


Vitamin E Deficiency

Disastrous effects on red blood cells

This vitamin E deficiency disease is called

hemolytic anemia

Sometimes observed in newborns

Disrupts the making of myelin, the protective

lipid covering of the nerve cell axons

Degeneration of the pigment in the rods and

cones of the retina


Vitamin E Requirement

Dietary Reference Intakes

Approximately 80% of the vitamin E from

dietary sources, including fortified foods, is

alpha-tocopherol

Approximately 20% comes from other forms

RDA for ages 14 and older:

15 mg for males and females


Food Sources of Vitamin E

Richest dietary sources of vitamin E are

vegetable oils

Sunflower, safflower, canola, corn, and olive

oils

Nuts and peanut butter

Certain vegetables and fruits, especially

tomatoes

Fortified ready-to-eat cereals



Vitamin K

Forms

Phylloquinone

• Found in plants, named for its chemical structure

• Major dietary form and is widely distributed in both

animal and vegetable foods

Menaquinone

• Synthesized by intestinal bacteria

Menadione

• Water-soluble analogue of vitamin K, can be absorbed

directly into the portal blood


Absorption of Vitamin K

Phylloquinone and menaquinone require

pancreatic lipase and bile salts for absorption

Packaged in the intestinal chylomicrons

Travel via the lymphatic system and then the

portal blood to the liver

In the liver, vitamin K is stored in small

amounts

Rapidly excreted after administration of

therapeutic doses


Functional Roles of Vitamin K

Blood Clotting

Initiates the synthesis of four blood-clotting

factors in the liver

Controls the liver synthesis of other proteins

that regulate the speed and duration of

coagulation

Bone Metabolism

Stimulates the synthesis of osteocalcin and

other proteins that are important in bone


Vitamin K Deficiency and Clinical

Application

Neonatology

Prophylactic dose soon after birth

Malabsorption problems

Defects in fat absorption impair vitamin K

absorption

Drug therapy

Anticlotting drugs require consistent intake of

vitamin K


Vitamin K Requirement


AI for men ages 19 and over is 120 µg/day

AI for women ages 19 and over is 90 µg/day

This amount of vitamin K is adequate to

preserve blood clotting

Unsure how much is needed for optimum

bone health


Food Sources of Vitamin K

Phylloquinone is found in many vegetables,

highest in dark green vegetables and liver

Menaquinones occur in milk, meat, and

certain cheeses


Water-Soluble Vitamins

Vitamin C

Associated with the search for the cause of

the ancient hemorrhagic disease scurvy

Absorption, Transport and Storage

Easily absorbed from the small intestine but

requires the presence of acid

Distributed throughout body tissues

Excess is excreted in the urine


Functions of Vitamin C

Antioxidant

Helps to take up the free oxygen arising from cell

metabolism, making it unavailable to fuel the

destructive actions of free radicals

Formation of intercellular cement

Helps build and maintain many body tissues,

including bone matrix, cartilage, dentin, collagen,

and connective tissue


Functions of Vitamin C – Cont’d

Support of general body metabolism

Important in many metabolically active tissues

Helps in the formation of hemoglobin and the

development of red blood cells by:

1. Promoting iron absorption

2. Assisting in the removal of iron from the protein-iron

complex called ferritin

Assists carnitine synthesis

Assists peptide hormone synthesis

Breakdown of drugs and other foreign molecules


Functions of Vitamin C – Cont’d

Clinical Applications

Wound healing

Fever and infection

Growth

Stress and body response

Chronic disease prevention


Vitamin C Requirement


Current Dietary Reference Intake takes into

account the need for antioxidant protection of

body tissues

For men the RDA is 90 mg

For women the RDA is 75 mg

Cigarette smokers require an additional 35

mg each day


Food Sources of Vitamin C

Best known food sources of vitamin C are

citrus fruits and tomatoes

Broccoli, salad greens, strawberries,

watermelon, cabbage, and sweet potatoes

are other good sources


The B Vitamins

All water soluble but with unique metabolic

functions

Serve as coenzyme partners with cell

enzymes that control energy metabolism and

build tissues

Thiamin, riboflavin, and niacin associated

with classic deficiency diseases


The B Vitamins – Cont’d

Recently discovered coenzyme factors—

vitamin B6 (pyridoxine), pantothenic acid, and

biotin

Important blood-forming factors—folate and

vitamin B12 (cobalamin)


Thiamin

A water-soluble and fairly stable vitamin

Destroyed in alkaline solutions

Name comes from its chemical ringlike

structure (thiazole ring)


Thiamin – Cont’d

Absorbed efficiently in the acid environment

of the upper small intestine before the acidity

of the food mass is buffered by the alkaline

secretions from the pancreas

Carbohydrate increases the need for thiamin,

whereas fat and protein spare thiamin


Functions of Thiamin

Control agent in energy metabolism

Combines with phosphorus to form hiamin

pyrophosphate (TPP)

TPP serves as a coenzyme in key reactions

involving glucose


Deficiency Symptoms of Thiamin

Classic deficiency disease is beriberi

Gastrointestinal: anorexia, constipation,

gastric atony, and poor HCl secretion

Nervous: Diminished alertness and reflex

responses, general apathy, and fatigue

Cardiovascular: Heart muscle weakens,

leading to cardiac failure and edema

Musculoskeletal: Chronic pain


Thiamin Requirement


Minimum requirement is 0.3 mg/1000 kcal

RDA is set at 1.2 mg for adult men and 1.1

mg for adult women

Extra is needed during pregnancy and

lactation

Excess thiamin is excreted by the kidneys

No UL has been established


Clinical Conditions That Influence

Thiamin Needs

Alcohol abuse

Acute illness or disease

Normal growth and development

Use of diuretics

Gastric bypass surgery


Food Sources of Thiamin

Widespread in plant and animal foods

Major sources in the American diet:

Whole and enriched breads and ready-to-eat

cereals, and legumes

Good food sources include lean pork and

beef


Riboflavin

Yellow-green fluorescent pigment that forms

yellowish brown, needlelike crystals

Easily destroyed by light and irradiation


Absorption of Riboflavin

Absorbed in the upper section of the small

intestine

Hindered by bulk fiber supplements such as

psyllium

Small amounts stored in the liver and kidney


Functions of Riboflavin

Part of the cell enzymes called flavoproteins

Active in both energy production and

deamination

Deamination is the removal of a nitrogen-

containing amino group from an existing amino

acid so a new amino acid can be formed


Deficiency Symptoms of

Riboflavin

Results in the condition termed

ariboflavinosis

Tissue inflammation and breakdown and poor

healing of even minor injuries

Sometimes occurs in newborns

Riboflavin is destroyed by light and so deficiency

can occur in infants treated with phototherapy


Riboflavin Requirement


RDA based on the amount needed to sustain

optimum levels of the flavoprotein enzymes

1.3 mg/day for adolescent and adult men

1.1 mg/day for adolescent and adult women

No UL set, but high-dose supplements still

carry a risk


Riboflavin Requirement – Cont’d

Risk Groups

Patients on hemodialysis

Pregnant and lactating women and infants

and children

People who engage in regular physical

activity


Food Sources of Riboflavin

Major sources of riboflavin are milk and

cheese

Riboflavin is destroyed by exposure to light;

therefore milk is usually packaged in cardboard or

opaque plastic containers

Breast milk stored in clear glass or plastic

containers may lose riboflavin

Other good sources of riboflavin are meat,

whole or enriched grains and ready-to-eat

cereals, and vegetables


Niacin

In 1937 a researcher at the University of

Wisconsin associated niacin with pellagra by

using it to cure a related disease (black

tongue) in dogs

Two forms of niacin have been identified:

1. Nicotinic acid

2. Nicotinamide


Niacin – Cont’d

Stable to acid and heat

Forms a white powder when crystallized

The amino acid tryptophan can be converted

to niacin in the body

60 mg tryptophan can produce 1 mg niacin

Measured in niacin equivalents (NE)


Functions of Niacin

Two coenzyme forms

1. Nicotinamide-adenine dinucleotide (NAD)

2. Nicotinamide-adenine dinucleotide phosphate

(NADP)

Partners with riboflavin in systems that

convert amino acids and glycerol to glucose

and oxidize the glucose to release energy


Functions of Niacin – Cont’d

Pharmacologic dosages of nicotinic acid have

been prescribed for cardiovascular patients in

an effort to raise blood high-density

lipoprotein (HDL) cholesterol levels and

reduce blood low-density lipoprotein (LDL)

cholesterol and triglyceride levels

This treatment carries some degree of risk

and requires careful supervision

At high levels, niacin is a vasodilator


Niacin Requirement


RDA measured in niacin equivalents (NE)

16 mg NE/day for adolescent and adult men

14 mg NE/day for adolescent and adult women


Niacin Requirement – Cont’d

Increase in niacin is needed for the following:

Rapid growth

Pregnancy and lactation

Physical activity

Tissue replacement after surgery or trauma


Food Sources of Niacin

Meat and dairy products are major sources of

niacin and also high in tryptophan

Other foods include peanuts, dried beans and

peas, and whole grain or enriched breads

and cereals

Corn and rice are relatively poor sources

because they are low in tryptophan


Pantothenic Acid

Synthesized by intestinal bacteria and

present in a wide variety of foods

Deficiency is unlikely

Absorption and Metabolism

Absorbed in the intestine and combines with

phosphorus to make the active molecule

acetyl coenzyme A (CoA)

No known toxicity or natural deficiency


Pantothenic Acid – Cont’d

Functions

Controls metabolic reactions involving

carbohydrates, fat, and protein

Requirements

5 mg/day for all adults will replace the

pantothenic acid lost daily in the urine

Food Sources

Found in both plant and animal foods

Good sources include egg yolk, milk, and broccoli


Biotin

Sulfur-containing vitamin

Natural deficiency is unknown

May occur in patients receiving long-term total

parenteral nutrition without biotin

Avidin, a protein found in raw egg white,

binds biotin and prevents its absorption

Cooking denatures this protein and destroys its

ability to bind biotin

No known toxicity for biotin


Biotin – Cont’d

Functions

Partners with acetyl coenzyme A (CoA) in reactions that transfer carbon dioxide from one compound to another Synthesis of fatty acids

Carbon dioxide fixation to form purines

Requirements

30 µg/day for all adults

Intestinal bacterial synthesis also adds to the body’s supply


Food Sources of Biotin

Found in many foods

Bioavailability varies greatly

Biotin in corn and soy is well absorbed

Biotin in wheat is generally unavailable


Vitamin B6 (Pyridoxine)

Chemical structure of vitamin B6 is a pyridine

ring

Three forms occur in nature:

Pyridoxine, pyridoxal, and pyridoxamine

All three forms are equally active in the body as

precursors of the coenzyme pyridoxal phosphate

(B6-PO4), or PLP


Absorption of Vitamin B6

(Pyridoxine)

Absorbed in the upper segment of the small

intestine

Stored in muscle but found in tissues

throughout the body


Functions of Vitamin B6

Coenzyme in more than 100 amino acid

reactions involving the synthesis of important

proteins:

Neurotransmitters

Amino group transfer

Sulfur transfer

Niacin

Hemoglobin

Immune function


Functions of Vitamin B6 – Cont’d

Coenzyme in fat metabolism

PLP converts the essential fatty acid linoleic acid

to arachidonic acid


Vitamin B6 Deficiency

Vitamin B6 holds a key to a number of clinical

problems:

Anemia

Central nervous system changes

Physiologic demands in pregnancy

Blood homocysteine levels

Medications


Vitamin B6 Requirement


High protein intake increases the need for

vitamin B6

Men and women ages 19 to 50 years need 1.3

mg/day

Men over age 50 require 1.7 mg/day, and women

of this age require 1.5 mg/day


Vitamin B6 Toxicity

Toxicity in women taking supplements 1000

times the RDA to alleviate premenstrual

syndrome

Interferes with muscle coordination and

damages the nervous system

UL is 100 mg/day


Food Sources of Vitamin B6

Many foods contain pyridoxine in small

amounts

Good sources include whole or fortified grain

products, legumes, meat, poultry, bananas,

and potatoes

Highest contributor of pyridoxine to the diets

of U.S. adults is ready-to-eat cereals


Folate

Named from Latin word for leaf because it was first extracted from dark leafy vegetables

Folic acid is seldom found naturally but is used in supplements 85% absorbed

Naturally occurring food folate is pteroylpolyglutamate 50% absorbed


Functions of Folate

Folate is the coenzyme with the important

task of attaching single carbons to metabolic

compounds

Key molecules formed in this process include:

Purines

Thymine

Hemoglobin


Folate Deficiency

Factors Associated With Folate Deficiency

Lack of gastric acid

Chemotherapy

Anticonvulsant medications


Folate Deficiency – Cont’d

Clinical Implications of Folate Deficiency

Anemia that responds to folate supplementation

Most likely in pregnant women, growing infants, and

young children

Inappropriately high blood homocysteine levels:

Uncertain effects on cardiovascular disease,

osteoporosis, and age-related cognitive impairment


Folate Requirements

Folate and Birth Defects

Plays essential role in the formation and

closure of the neural tube in the early weeks

of fetal development

Demands that mother be in good folate status

before becoming pregnant; supplementation

after pregnancy is confirmed too late to

prevent damage to the fetus


Folate Requirements – Cont’d

Folate and Birth Defects – Cont’d

Folate deficiency early in pregnancy can

result in a neural tube defect in the

developing fetus

Mandatory folate fortification of flour or uncooked

grain

Incidence of NTDs has declined

Concern that it may mask vitamin B12 deficiency


Folate Requirements – Cont’d


RDA for adolescents and adults of all ages is

400 µg/day

Increases to 600 µg/day in pregnancy to

support fetal and maternal tissue growth

Women of childbearing age should consume

at least 400 µg/day of folate

Fortification has increased intakes by as

much as 200 µg/day


Food Sources of Folate

Good sources include dark green leafy

vegetables, citrus fruits, tomatoes,

cantaloupe, and legumes

Fortified grains and ready-to-eat cereals are

important sources


Vitamin B12 (Cobalamin)

A complex red crystal of high molecular

weight with a single cobalt atom at its core

Occurs as a protein complex in foods of

animal origin only


Absorption of Vitamin B12

(Cobalamin)

Gastric acid is required to separate the

vitamin from its protein complex

Vitamin is bound to a specific glycoprotein

called intrinsic factor secreted by the mucosal

cells lining the stomach

Intestinal absorption occurs in the ileum


Functions of Vitamin B12

Participates in amino acid metabolism and

the formation of the heme portion of

hemoglobin

Involved in the synthesis of important lipids

and proteins that form the myelin sheath

covering the nerves of the brain and spinal

cord


Vitamin B12 Deficiency

Deficiency Symptoms

Disrupted formation of red blood cells,

resulting in production of megaloblastic cells

(megaloblastic anemia)

Damage to the nerves of the brain and spinal

cord with changes in cognitive function,

judgment, and personality


Vitamin B12 Deficiency – Cont’d

Deficiency Diseases

Pernicious anemia

Results from lack of intrinsic factor

Treated with injections of vitamin B12


Vitamin B12 Deficiency – Cont’d

Deficiency Diseases – Cont’d

Vitamin B12 deficiency in older adults

Results from a lack of gastric acid

Treated with injections of vitamin B12 or use of B12

fortified foods (this form of B12 does not require

gastric acid for absorption)

Excessively high blood folate levels

ameliorate anemia, but exacerbate cognitive

losses


Vitamin B12 Requirements

Needed in minute amounts

RDA is 2.4 µg for both younger and older

adults


Food Sources of Vitamin B12

Found naturally only in animal foods

Rich sources include lean meat, fish,

poultry, milk, eggs, and cheese

Vitamin B12—fortified grains, cereals,

juices, and soy milk or supplements

Ch 6 ppt

Health & Medicine

Transcript of Ch 6 ppt