Download NTR 150_Vitamins and Antioxidants

Vitamins &
Antioxidants
Two Classes

Fat-Soluble
–
–
–
–
A
D
E
K

Water-Soluble
– Vitamin C
– 9 B-vitamins
•
•
•
•
•
•
•
•
•
Thiamin
Riboflavin
Niacin
Pantothenic Acid
B6
B12
Folate
Biotin
Choline
Effects of Solubility

Solubility affects absorption, transport,
storage, and excretion

Fat-soluble vitamins
 Lipid-like; mix well with fats
 Require bile for digestion and absorption;
absorbed along with fat
 Travel through lymphatic system to blood
 Excesses are stored
 Liver and adipose tissue
 Intakes can vary day to day without deficiency
risk, but toxicity possible with high doses
Water-Soluble Vitamins

Absorbed directly into blood
– No carriers needed

Kidneys filter out excesses of most (not
all!)
– Excretion in the urine

Most are not stored in the body
– Need frequent replenishing

Megadoses of some can still cause
adverse effects
More is not necessarily better…
Bioavailability



Quantity provided by food
Amount absorbed and used by body
Factors influencing bioavailability
 Efficiency of digestion
 Nutrition status
 Method of food preparation
 Source of nutrient
 Other foods consumed at same time
Antioxidants

Some vitamins
–E
–C
– Beta-carotene (provitamin A)

Many phytochemicals
 Body’s own antioxidant enzymes assisted by
some minerals
–
–
–
–
Selenium
Zinc
Copper
Manganese
Free Radicals

Free radical: active oxidant
 Compound with one or more unpaired
electrons
 Look to steal electron from vulnerable
compound
 Electron-snatching chain reaction: damage
to DNA, lipids, and cell structures

Free radical production
 Normal bodily functions
 Environmental factors
Free Radicals & Antioxidants
Free Radicals and Disease

Antioxidants
 Neutralize free radicals
 Donate an electron, but remain stable

Free radical attacks
 Some are helpful
 Immune system destruction of viruses,
bacteria
 Most cause damage
Free Radicals and Disease

Free radical damage
 Interferes with cell function
 Contributes to disease progression and
aging
 Oxidation of polyunsaturated fatty acids
in lipoproteins and membranes
 Alteration of DNA, RNA, and proteins
 Illicits inflammatory response
Free-Radical Damage
Free Radicals and Disease

Body’s natural defenses and repair
systems
 Enzymes that destroy free-radicals and
repair damage
 Not 100% effective
 Less effective with age

Dietary antioxidants help to defend
against oxidative stress
Why do we need antioxidants?
Limit free-radical formation
 Destroy free radicals or precursors
 Stimulate antioxidant enzymes
 Repair oxidative damage
 Support healthy immune system

Foods, Supplements, or Both?

Replenish antioxidants regularly
 Foods
 Contain other valuable nutrients
 Antioxidant actions of fruits and
vegetables are greater than their
nutrients alone
 Supplements
 Research inconclusive
 Contents are limited

Physiological levels vs.
pharmacological doses