Lesson E1 - Vitamins Flashcards
(27 cards)
What is a vitamin?
A vitamin is a substance essential for the maintenance of normal metabolic functions, but is not
made in the body and therefore must be provided from an outside source
How were vitamins discovered?
Vitamins were discovered by studying several deficiency diseases.
water soluble vitamins are
vitamin C and eleven vitamins in the B group
fat soluble vitamins are
A, D, E and K)
Are vitamins drugs?
When a healthy person obtains vitamins from a healthy diet, we do not consider the vitamins in
the food as drugs. However, when vitamins are consumed in the chemically pure form as a
tablet, they are considered to be drugs.
DRIs
Dietary recommended intakes.
EAR
Estimated average requirement.
RDA
Recommended daily allowance.
AI
Adequate intake
UL
Upper limit
Vitamins are required as dietary supplements in the following situations:
- Inadequate intake:
(a) Individuals who consume an inadequate diet for reasons of poverty and/or geography. A
good example is the aboriginal people living in the Canadian north.
(b) Individuals consuming a diet consisting of one major food. An example is black groups in
South Africa living on a corn diet.
(c) Individuals consuming an eccentric diet due to a psychiatric disturbance.
(d) Individuals who have particular ideas leading to an idiosyncratic diet.
(e) Individuals who, for religious reasons, consume an inadequate diet.
(f) Alcohol-dependent individuals who have an inadequate food intake since they obtain a
large number of calories from alcohol.
(g) Individuals on restrictive diets.
(h) Individuals on restricted diets for disease management.
Vitamins are required as dietary supplements in the following situations:
- Disturbances in absorption:
(a) Prolonged diarrhea.
(b) Liver disease.
(c) An individual taking antibiotics that alter intestinal bacteria. Vitamin K and biotin (one of
the vitamin B group) are derived from intestinal bacteria.
Vitamins are required as dietary supplements in the following situations:
- Increased tissue requirements:
In healthy individuals:
(a) During growth.
(b) During periods of hard physical work, e.g. working deep underground in a gold mine
under hot and humid conditions.
(c) Pregnancy, lactation (breast feeding), menstruation.
(d) Stress.
Vitamins are required as dietary supplements in the following situations:
In illness:
(a) Hyperthyroidism (overactive thyroid).
(b) Fever.
(c) Tissue wasting.
Consequences of excessive intake of vitamins:
Nutritional approach: This is the rational approach where one selects a diet aimed at
supplying the RDA for each vitamin or a multivitamin preparation which supplies the RDA of each vitamin.
Megavitamin approach: This approach is based on the delusion that “if a small dose is
good, a larger dose must be better.”
Mechanism of action and results of deficiency:
Cells are held together in organs by a framework of collagen and intercellular ground substance. Collagen and intercellular ground substance require vitamin C for their formation. If adequate
vitamin C is not provided, then cells will not be held together adequately. Thus, a defect in the
framework holding cells together in blood vessels leads to bleeding. These conditions are associated with severe vitamin C deficiency, namely scurvy.
The B group of vitamins, traditionally consisting of eleven members, are grouped in a single
class because they were originally isolated from the same sources, namely liver and yeast. Some
of the B vitamins and their RDA’s are
Folate 200 μg Niacin (vitamin B3) 19 mg Riboflavin (vitamin B2) 1.7 mg Thiamin (vitamin B1) 1.5 mg Pyridoxine (vitamin B6) 2.0 mg Cyanocobalamin (vitamin B12) 2.0 μg Biotin 30-100ug Ranges of recommended intakes Pantothenic acid (vitamin B5) 4-7 mg
Folate:
It has been shown to be important to supplement the diet of
women of childbearing age with 400
μg of folic acid per day. The reason for the supplement is the demonstration that such a
supplement can markedly decrease the incidence of neural tube defects (such as spina bifida) in
their offspring.
Vitamin A: Effects of deficiency:
(a) Growth and development will be retarded.
(b) Vitamin A is a constituent of a complex molecule, called rhodopsin, in rods of the eye, and
is required for night vision. Deficiency of vitamin A leads to night blindness and to drying
of the surface of the eye, a condition called xerophthalmia (dry eye). When deficiency is
severe, visual impairment and blindness may result.
(c) Deficiency of vitamin A leads to changes in cells lining the bronchioles in the lung and
enhances the opportunity for respiratory infection.
(d) Deficiency of vitamin A leads to a dry, thick and horny skin.
Vitamin A: Therapeutic Uses
(a) Treatment of vitamin A deficiency. Vitamin A deficiency is a serious nutritional deficiency
disease. It is particularly common in South East Asia, Africa, Central and South America,
and the Middle East, resulting in irreversible blindness in approximately one-quarter
million children per year. Obviously extreme poverty is a major reason.
(b) Administration in periods of increased requirement such as infancy, pregnancy and
lactation.
(c) Vitamin A derivatives are used in the treatment of acne and some other skin diseases
Prior to the discovery of vitamin D, a high percentage of urban children, especially those living
in temperate zones, developed
rickets
Vitamin D undergoes
conversion in the liver to 25-hydroxyvitamin D, which in turn is converted in the kidney to the
active form of the vitamin, namely
1,25-dihydroxyvitamin D.
Actions of vitamin D:
(a) Increases the absorption of calcium and phosphate from the intestine. The calcium and
phosphate is utilized for formation of new bone.
(b) The blood calcium level must be maintained within prescribed limits for optimal health and
vitamin D is involved in regulation of the blood calcium level.
(c) Vitamin D is involved in removal of calcium from older bone.
Results of vitamin D deficiency:
(a) Decreased absorption of calcium and phosphate from intestine.
(b) Decrease in blood calcium level.
(c) Calcium removed from bone in attempt to maintain blood calcium level. As a result,
defective bone growth occurs in infants and children leading to bowleggedness – a
condition referred to as rickets. Rickets also occurs in adults.
