Drugs

The History, Use
 And
 Effectiveness Of Medicinal Drugs
 
The science and the art of treating, diagnosing, and
preventing disease is known as the field of Medicine. It is
a science because it is based on knowledge, gained through
careful study and experimentation. It is an art because it
depends on how skillfully doctors and other medical workers
apply this knowledge when dealing with patients. 

In prehistoric times, Medicine was a vague field, mostly
incorporated with magic and superstition. The first
physicians were the tribal priests who tried to pacify the
gods or drive out the evil spirits. In ancient times, the
Egyptian civilization was the first group of people to make
important medical progress. The world's first physician
known by name was the Egyptian Imhotep, who lived about
2700 B.C. During the Middle Ages, the Moslems made enormous
contributions to medicine in their use of drugs. The first
truly scientific studies of the human body began during the
Renaissance. The scientific study of disease developed
during the 1800's and was led by Rudolf Virchow, a German
physician and scientist. 

The study of the effects that chemicals have on living
things is called pharmacology. It is a recent science, but
it is linked with one of the oldest -- the giving of
remedies to relieve disease. Pharmacology began during the
1900's with the rise of chemistry. For the first time, the
crude plants and mineral materials that act on living
tissues could be analyzed, separated and used as a drug or
medicine.
 
Many early treatments didn't actually heal the patient, but
just gave him a slight euphoria from the pain. In today's
culture, some of the drugs of our ancestors are considered
to be harmful and are classified as illegal. Examples of
such are marijuana and opium which were key in the Chinese,
and Native American medical system. The origin of drugs
vary from common plants, (Aspirin, Digitalis, Ergot, Opium,
Quinine, Reserpine) to minerals, (Boric Acid, Epsom Salts,
Iodine) or synthetic compounds. The difference in a drug
from being helpful to being deadly is in the dosage that is
administered. This process is known as Serum Monitoring. 

In addition to determining the dosage of the medication,
the "risk-to-benefit" ratio of the drug must be considered
as well. A drug might heal one ailment but in turn cause
another problem. An example of this is the drug niridazole,
which helps schistosomaisis but is known to cause cancer. 

The national government has some control in the area of
drug use and has issues certain regulations. For example
drugs have been classified into two categories; Proprietary
and Ethical. Proprietary drugs are sold over the counter
and promote less addiction that Ethical drugs which can
only be obtained legally with a written prescription from a
registered doctor. Jurisdiction of illegal drugs which
produce a strong addiction is given to the Drug Enforcement
Administration of the U.S. Department of Justice. The most
important factor about doctor prescribed drugs is that the
doctor is aware of any other drugs which the patient might
be taking, and therefore prevent adverse reactions between
medications.
 
ASPIRIN 

Acetylsalicylic acid, commonly known as aspirin is one of
the most widely used analgesics in the world". Used by
Ancient Greeks and Native Americans it was used to reduce
fever and pain and could also be used as an
anti-inflammatory agent. It interferes with tissue
contractions of the prostaglandin which are chemicals
involved in the production of inflammation and pain. It
modifies the temperature-regulating portion of the brain,
dilating blood vessels in the skin and increases
perspiration which in turn cools the body reducing fever. _
_ Aspirin also prevents the production of thromboxane which
plays a key role in coagulation cascade, which slows blood
clotting and is helpful in preventing heart attacks and
strokes. It is derived from the bark of the willow tree,
and its activity is produced from chemicals called
salicylates. _
 
Charles Gerhardt a French chemist first synthesized the
acetyl derivative from the salicylic acid in 1853
developing the first type of aspirin, but Felix Hoffman a
German chemist was the first to realize its medical value
in 1893. Over a long period of constant use aspirin can
cause iron deficiency, gastric ulcers, kidney damage and if
given to children having chicken pox or influenza could
cause the risk of contracting the fatal brain disease known
as Reye's syndrome.
 
Usage of Aspirin varies. Short term use of about 3"6-10
days" is recommended without physician supervision but long
term use requires periodic evaluations and dosage
restrictions.
 
Side effects also vary with the individual. They could
include mild drowsiness, allergic reactions, skin rash,
hives, nasal discharge, stomach irritation, heart burn,
nausea, vomiting, constipation and in extreme cases erosion
of the stomach lining, activation of a peptic ulcer, bone
marrow depression, hepatitis, and kidney damage. Overdosing
on this drug produces side effects such as stomach
distress, nausea, vomiting, ringing in the ears, sweating,
stupor, deep and rapid breathing, twitching, and
convolutions.
 
Aspirin was the first non-steroidal anti-inflammatory drug
(NASID) but by far not the last. One and a half million
Americans suffer from heart attacks each year and about
200,000 suffer from heart related deaths. Aspirin helps
millions of people each year because it prevents premature
blood clotting. No other NSAID can compare with the price
or efficacy of aspirin but ibuprofen can come very close.
Where aspirin might take up to 12 doses to relieve pain
over a long period a strong dosage of ibuprofen could help
the patient in one dose.
 
Even though Ibuprofen works as well as aspirin, care must
be taken with its usage. It does not irritate the stomach
as much as aspirin, however, it could damage the kidneys.
Another factor to consider between aspirin and ibuprofen is
price. A thirty day supply of aspirin could cost $3.95
whereas a thirty day supply of ibuprofen could cost $22.95.
 
New studies prove that aspirin also has been prescribed to
counteract migraine headaches, cataracts, gallstones,
diabetic eye problems, insomnia, weight loss for women,
wheat intolerance, leprosy and even hip replacement
complications. 

SULFA DRUGS 

Sulfonamides, the chemical name for sulfa drugs were the
first chemical compounds to provide safe and effective
treatment for most common bacterial infections. Before the
use of penicillin after the mid 1940's, Sulfa drugs played
a major role in antibacterial treatment. This resulted in a
sharp decrease in deaths from bacterial infections. In
today's modern medical system, sulfa drugs are used to
treat patients of urinary tract infections. 

Sulfa
 
Sulfa in its natural form is a tasteless, odorless, light
yellow solid, once forcefully fed to children in the belief
that it was good for their health. Sulfa compounds, found
in dairy products and eggs, are an essential dietary
ingredient. Instead of killing bacteria, sulfa drugs
prevent them from multiplying, making it easier for the
bodies' natural defenses to overcome and destroy them.
Bacteria require certain chemicals known as
6"para-aminobenzoic acids" to multiply, sulfa drugs
resemble the chemical structure of the acids and can be
absorbed by the bacteria. The sulfa drugs combine with the
outer shells of the bacteria, therefore not allowing the
real acids to penetrate.
 
All bacteria are not reactant to sulfonamides and have to
be screened by the physician to see if it is necessary to
take a more serious action. Sulfa drugs can be taken orally
which is most common, or by an injection just beneath the
skin. In former medical history they were used to treat
pneumonia, dysentery, blood poising, cellulitis, bubonic
plague, and conjunctivitis.
 
Since the recognition of penicillin as an effective
bacterial assailant and some bacteria becoming resistant to
sulfonamides physicians have been less likely to prescribe
them since the late 1940's. The combination of
sulfamethoxazole and trimethoprim have given a new usage
for sulfa drugs, now they can be used for such ailments as
middle ear infections, shigellosis and recurring urinary
tract infections.
 
Paul Gelmo, in 1908, discovered the first sulfa drug
accidentally while looking for dyes to better color woolen
clothing. In 1953, a German pathologist named Gerhard
Domagk reported that this dye killed streptococcal bacteria
in mice. 

In the beginning, doctors encountered major problems when
administering the drug sulfanilamide because it
crystallized in the urine of the patient causing kidney
damage. Later development of water soluble sulfa drugs
solved the problem of crystallization in the urine and gave
the hope of a longer life span to people. 

ANTIBIOTICS
 
In the ancient language of Greek the term antibiotic meant
"against life". They are chemical substances produced by
one organism that in turn is destructive to another. This
process traditionally has been called antibiosis and is the
opposite of symbiosis. An antibiotic is a type of
chemotherapeutic agent which has a toxic effect on certain
types of disease-producing microorganisms without acting
dangerously on the patient. 

Some chemotherapeutic agents differ from antibiotics in
that they are not secreted by microorganisms, as are
antibiotics, but rather are made synthetically in a
chemical laboratory. Examples of these are quinine, used
against malaria; arsphenamine, used against syphilis; the
sulfa drugs, used against a wide variety of diseases,
notably pneumonia; and the quinolones, used against
hospital-derived infections (zoonoses). A few antibiotics,
among them penicillin and chloramphenicol, have now been
produced synthetically also. 

The first observation of what would now be called an
antibiotic effect was made in the 19th century by the
French chemist Louis Pasteur, who discovered that certain
saprophytic bacteria can kill anthrax germs. Around the
year 1900, the German bacteriologist Rudolf von Emmerich
isolated a substance called pyocyanase, which can kill the
germs of cholera and diphtheria in the test tube. It was
not useful, however, in curing disease. In the 1920's, the
British bacteriologist Sir Alexander Fleming, who later
discovered penicillin, found a substance called lysozyme.
He found it in many of the secretions of the body such as
tears and sweat, and in certain other plant and animal
substances. Lysozyme has a strong antimicrobial activity,
but mainly against harmless bacteria.
 
(Sir Alexander Fleming) Discovery of Penicillin 

The research of Alexander Fleming in 1928 led to the
discovery of penicillin, an important antibiotic derived
from the mold Penicillin notatum. Penicillin is effective
against a wide range of disease-causing bacteria. It acts
by killing bacteria directly or by inhibiting their growth.
 
Penicillin, the archetype of antibiotics was discovered by
accident in 1928 by Fleming. He showed its effectiveness in
laboratory cultures against many disease-producing
bacteria, such as those that cause gonorrhea and certain
types of meningitis and bacteria (blood poisoning);
however, he performed no experiments on animals or humans.
Penicillin was first used on humans by the British
scientists Sir Howard Florey and Earnest Chain during the
1940-41 winter.
 
The first antibiotic to be used in the treatment of human
diseases was tyrothricin (one of the purified forms of
which was called gramicidin), which was isolated from
certain soil bacteria by the American bacteriologist, Rene
Jules Dubos in 1939. This substance was too toxic for
general use, but it is employed in the external treatment
of certain infections. Other antibiotics produced by
actinomycetes, filamentous and branching bacteria,
occurring in soil have proved more successful. One of these
is streptomycin, discovered in 1944 by the American
microbiologist Selman Waksman and his associates. It is
effective against many diseases, including several in which
penicillin is useless, especially tuberculosis. 

Since then, such antibiotics as chloramphenicol, the
tetracyclines, erythromycin, neomycin, nystatin,
amphotericin, cephalosporins, and kanamycin have been
developed and may be used in the treatment of infections
caused by some bacteria, fungi, viruses, rickettsia, and
other microorganisms. 

In clinical treatment of infections, the causative organism
must be identified and the antibiotics to which it is
sensitive must be determined in order to select an
antibiotic with the greatest probability of killing the
infecting organism. Recently, strains of bacteria have
arisen that are resistant to commonly used antibiotics; for
example, gonorrhea-causing bacteria that high doses of
penicillin are not able to destroy may transfer this
resistance to other bacteria by exchange of genetic
structures called plasmids. Some bacteria have become
simultaneously resistant to two or more antibiotics by this
mechanism. New antibiotics that circumvent this problem,
such as the quinolones, are being developed.
 
The cephalosporins, for instance, kill many of the same
organisms that penicillin does, but they also kill strains
of those bacteria that have become resistant to penicillin.
Often the resistant organisms arise in hospitals, where
antibiotics are used most often, especially to prevent
infections from surgery. Another problem in hospitals is
that many old and very ill patients develop infections from
organisms that are not pathogenic in healthy persons, such
as the common intestinal bacterium Escherichia coli. New
antibiotics have been synthesized to combat these
organisms. 

Fungus infections have also become more common with the
increasing use of chemotherapeutic agents to fight cancer,
and more effective antifungal drugs are being sought. The
search for new antibiotics continues in general, as
researchers examine soil molds for possible agents. Among
those found in the 1980s, for example, are the
monobactams", which may also prove useful against hospital
infections. 

Antibiotics are found in other sources as well, such as the
family of magainins discovered in the late 1980s in frogs;
although untested in humans as yet, they hold broad
possibilities". Antibiotics have also been used effectively
to foster growth in animals. Concern has arisen, however,
that this widespread use of antibiotics in animal feed can
foster the emergence of antibiotic-resistant organisms that
may then be transmitted to human beings.
 
ANTIHISTAMINES 

Antihistamines are drugs that block the action of
histamine. Histamine, also known as histamine phosphate, an
amine (beta-imidazolyl-ethylamine, ergamine, or ergotidime)
that is a normal constituent of almost all animal body
cells. Histamine is also found in small quantities in ergot
and purified meat products and is produced synthetically
for medicinal purposes. In the body, it is synthesized in a
type of leukocyte called a basophil or mast cell. In
response to certain stimuli, these cells release histamine
which immediately cause a dilation of the blood vessels.
This dilation is accompanied by a lowering of blood
pressure and an increased permeability of the vessel walls,
so that fluids escape into the surrounding tissues. Such
reaction may result in a general depletion of vascular
fluids, causing a condition known as histamine poisoning or
histamine shock. 

Allergic reactions in which histamine is released,
resulting in the swelling of body tissue, show similarities
to histamine poisoning; the two may be basically similar,
and the two conditions are treated similarly. The release
of histamine might also be partly responsible for difficult
breathing during an asthma attack. 

In the 1930s the Italian pharmacologist Daniel Bovet, who
live in 1907-1972, working at the Pasteur Institute in
Paris, discovered that certain chemicals counteracted the
effects of histamine in guinea pigs. The first
antihistamines were too toxic for use on humans, but by
1942 they had been modified for use in the treatment of
allergies". More than 25 antihistamine drugs are now
available.
 
Histamine also causes contraction of involuntary muscles,
especially of the genital tract and gastrointestinal canal,
with an accompanying secretion by associated glands.
Because histamine stimulates the flow of gastric juices, it
is used diagnostically in patients with gastric
disturbances. One drug effective in treating gastric ulcers
acts by antagonizing the action of histamine. The ability
of the body to localize infections may be due to the
secretion of histamine and the subsequent increased local
blood supply and increased permeability of the blood
vessels. 

Antihistamines are used primarily to control symptoms of
allergic conditions such as hay fever. They alleviate runny
nose and sneezing and to a lesser extent, minimize
conjunctivitis and breathing difficulties. Antihistamines
can also alleviate itching and rashes caused by food
allergy. Chemically, antihistamines comprise several
classes and a person who does not obtain relief from one
type may benefit from another. Side effects of these drugs
can include drowsiness, loss of concentration, and
dizziness. People taking antihistamines should not drink
alcoholic beverages or perform tasks requiring mental
alertness, such as driving. A few antihistamines, such as
terfenadine and astemizole, are nonsedating. Although
antihistamines are included in many over-the-counter cold
remedies, their usefulness in such preparations is
questionable.
 
Antihistamines may relieve symptoms of allergy accompanying
a cold, or they may have an anticholinergic effect that
dries cold secretions, but they do not have any influence
on viral infections, which are the cause of colds .
Moreover, the drying effect may be undesirable, especially
for persons with bronchial infection, glaucoma, or urinary
tract difficulties. 

Although there are not many alternate drugs that have the
same properties as antihistamines some non-drug treatments
are also effective against allergies. The use of
High-Efficiency-Particulate-Arresting (HEPA) filters,
eliminate microscopic particles which cause allergies. The
use of mattress covers decrease the reaction to dust mites
in the mattress itself. These treatments are not equivalent
to drug use but could decrease the amount of allergenic
agents in the household air. Vitamin C also plays a role in
the elimination of allergic reactions. Researchers at the
University of California have found that patients that
suffer from atopic dermatitis benefited from large dosages
of vitamin C.
 
THE HISTORY, USE AND EFFECTIVENESS OF VITAMINS AND NUTRIENT
SUPPLEMENTS 

A Vitamin is any organic compound required by the body in
small amounts for metabolism, to protect health, and for
proper growth in children. Vitamins also assist in the
formation of hormones, blood cells, the chemicals of the
nervous-system, and genetic material. The various vitamins
are not chemically related, and most differ in their
physiological actions. They generally act as catalysts,
combining with proteins to create metabolically active
enzymes that in turn produce hundreds of important chemical
reactions throughout the body. Without vitamins, many of
these reactions would slow down or stop. The intricate ways
in which vitamins act on the body, however, are still far
from clear. 

The 13 well-identified vitamins are classified according to
their ability to be absorbed in fat or water. The
fat-soluble vitamins A, D, E, and K are generally consumed
along with fat-containing foods, and because they can be
stored in the body's fat, they do not have to be consumed
every day. The water-soluble vitamins, the eight B vitamins
and vitamin C, cannot be stored and must be consumed
frequently, preferably every day. 

The body can manufacture only vitamin D, and all others
must be derived from the diet. Lack of them causes a wide
range of metabolic and other dysfunctions. In the U.S.,
since 1940, the Food and Nutrition Board of the National
Research Council has published recommended dietary
allowances for vitamins, minerals, and other nutrients.
Expressed in milligrams or international units for adults
and children of normal health, these recommendations are
useful guidelines not only for professionals in nutrition
but also for the growing number of families and individuals
who eat irregular meals and rely on prepared foods, many of
which are now required to carry nutritional labeling. 

A well-balanced diet contains all the necessary vitamins,
and most individuals who follow such a diet can correct any
previous vitamin deficiencies. However, persons who are on
special diets, who are suffering from intestinal disorders
that prevent normal absorption of nutrients, or who are
pregnant or lactating may need particular vitamin
supplements to bolster their metabolism. 

Beyond such real needs, vitamin supplements are also often
believed to offer "cures" for many diseases, from colds to
cancer; but in fact the body quickly eliminates most of
these preparations without absorbing them. In addition, the
fat-soluble vitamins can block the effect of other vitamins
and even cause severe poisoning when taken in excess.
Vitamin A is a pale yellow primary substance derived from
carotene. It affects the formation and maintenance of skin,
mucous membranes, bones, and teeth, vision, and
reproduction. An early deficiency symptom is night
blindness which is the difficulty in adapting to darkness.
Other symptoms are excessive skin dryness and lack of
mucous membrane secretion. This allows bacterial invasion,
and dryness of the eyes due to a malfunctioning of the tear
glands, a major cause of blindness in children in
developing countries. 

The body obtains vitamin A in two ways. One is by
manufacturing it from carotene, a vitamin precursor found
in such vegetables as carrots, broccoli, squash, spinach,
kale, and sweet potatoes. The other is by absorbing
ready-made vitamin A from plant-eating organisms. In animal
form, vitamin A is found in milk, butter, cheese, egg yolk,
liver, and fish-liver oil. Although one-third of American
children are believed to consume less than the recommended
allowance of vitamin A, sufficient amounts can be obtained
in a normally balanced diet rather than through
supplements. Excess vitamin A can interfere with growth,
stop menstruation, damage red blood corpuscles, and cause
skin rashes, headaches, nausea, and jaundice. 

Known also as vitamin B complex, these are fragile,
water-soluble substances, several of which are particularly
important to carbohydrate metabolism. Thiamine, or vitamin
B1, a colorless, crystalline substance, acts as a catalyst
in carbohydrate metabolism, enabling pyruvic acid to be
absorbed and carbohydrates to release their energy.
Thiamine also plays a role in the synthesis of
nerve-regulating substances. Deficiency in thiamine causes
beriberi, which is characterized by muscular weakness,
swelling of the heart, and leg cramps and may, in severe
cases, lead to heart failure and death. 

Many foods contain thiamine, but few supply it in
concentrated amounts. Foods richest in thiamine are pork,
organ meats such as liver, heart, and kidney, brewer's
yeast, lean meats, eggs, leafy green vegetables, whole or
enriched cereals, wheat germ, berries, nuts, and legumes.
Milling of cereal removes those portions of the grain
richest in thiamine; consequently, white flour and polished
white rice may be lacking in the vitamin. Widespread
enrichment of flour and cereal products has largely
eliminated the risk of thiamine deficiency, although it
still occurs today in nutritionally deficient alcoholics. 

Riboflavin, or vitamin B2, like thiamine, serves as a
coenzyme, one that must combine with a portion of another
enzyme to be effective, in the metabolism of carbohydrates,
fats, and, especially, respiratory proteins. It also serves
in the maintenance of mucous membranes. Riboflavin
deficiency may be complicated by a deficiency of other B
vitamins; its symptoms, which are not as definite as those
of a lack of thiamine, are skin lesions, especially around
the nose and lips, and sensitivity to light. The best
sources of riboflavin are liver, milk, meat, dark green
vegetables, whole grain and enriched cereals, pasta, bread,
and mushrooms. 

Niacin, or vitamin B3, also works as a coenzyme in the
release of energy from nutrients. A deficiency of niacin
causes pellagra, the first symptom of which is a
sunburnlike eruption that breaks out where the skin is
exposed to sunlight. Later symptoms are a red and swollen
tongue, diarrhea, mental confusion, irritability, and, when
the central nervous system is affected, depression and
mental disturbances. The best sources of niacin are liver,
poultry, meat, canned tuna and salmon, whole grain and
enriched cereals, dried beans and peas, and nuts. The body
also makes niacin from the amino acid tryptophan. Megadoses
of niacin have been used experimentally in the treatment of
schizophrenia, although no experimental proof has been
produced to show its efficacy. In large amounts it reduces
levels of cholesterol in the blood, and it has been used
extensively in preventing and treating arteriosclerosis.
Large doses over long periods cause liver damage. 

Pyridoxine, or vitamin B6, is necessary for the absorption
and metabolism of amino acids. It also plays roles in the
use of fats in the body and in the formation of red blood
cells. Pyridoxine deficiency is characterized by skin
disorders, cracks at the mouth corners, smooth tongue,
convulsions, dizziness, nausea, anemia, and kidney stones.
The best sources of pyridoxine are whole (but not enriched)
grains, cereals, bread, liver, avocados, spinach, green
beans, and bananas. Pyridoxine is needed in proportion to
the amount of protein that is consumed. 

Cobalamin, or vitamin B12, one of the most recently
isolated vitamins, is necessary in minute amounts for the
formation of nucleoproteins, proteins, and red blood cells,
and for the functioning of the nervous system. Cobalamin
deficiency is often due to the inability of the stomach to
produce glycoprotein, which aids in the absorption of this
vitamin. Pernicious anemia results, with its characteristic
symptoms of ineffective production of red blood cells,
faulty myelin (nerve sheath) synthesis, and loss of
epithelium the membrane lining of the intestinal tract.
Cobalamin is obtained only from animal sources such as
liver, kidneys, meat, fish, eggs, and milk. Vegetarians are
advised to take vitamin B12 supplements. 

Folic acid, or folacin, is a coenzyme needed for forming
body protein and hemoglobin; its deficiency in humans is
rare. Folic acid is effective in the treatment of certain
anemias and sprue. Dietary sources are organ meats, leafy
green vegetables, legumes, nuts, whole grains, and brewer's
yeast. Folic acid is lost in foods stored at room
temperature and during cooking. Unlike other water-soluble
vitamins, folic acid is stored in the liver and need not be
consumed daily. 

Pantothenic acid, another B vitamin, plays a
still-undefined role in the metabolism of proteins,
carbohydrates, and fats. It is abundant in many foods and
is manufactured by intestinal bacteria as well. 

Biotin, a B vitamin that is also synthesized by intestinal
bacteria and widespread in foods, plays a role in the
formation of fatty acids and the release of energy from
carbohydrates. Its deficiency in humans is unknown. This
well-known vitamin is important in the formation and
maintenance of collagen, the protein that supports many
body structures and plays a major role in the formation of
bones and teeth. It also enhances the absorption of iron
from foods of vegetable origin. Scurvy is the classic
manifestation of severe ascorbic acid deficiency. Its
symptoms are due to loss of the cementing action of
collagen and include hemorrhages, loosening of teeth, and
cellular changes in the long bones of children. 

Assertions that massive doses of ascorbic acid prevent
colds and influenza have not been borne out by carefully
controlled experiments. In other experiments, however,
ascorbic acid has been shown to prevent the formation of
nitrosamines which are compounds found to produce tumors in
laboratory animals and possibly also in humans. Although
unused ascorbic acid is quickly excreted in the urine,
large and prolonged doses can result in the formation of
bladder and kidney stones, interference with the effects of
blood-thinning drugs, destruction of B12, and the loss of
calcium from bones. 

Sources of vitamin C include citrus fruits, fresh
strawberries, cantaloupe, pineapple, and guava. Good
vegetable sources are broccoli, Brussels sprouts, tomatoes,
spinach, kale, green peppers, cabbage, and turnips. This
vitamin is necessary for normal bone formation and for
retention of calcium and phosphorus in the body. It also
protects the teeth and bones against the effects of low
calcium intake by making more effective use of calcium and
phosphorus. 

Also called the sunshine vitamin, vitamin D is obtained
from egg yolk, liver, tuna, and vitamin-D fortified milk.
It is also manufactured in the body when sterols, which are
commonly found in many foods, migrate to the skin and
become irradiated. Vitamin D deficiency, or rickets, occurs.