Vitamins
The term vitamin is derived from the words vital and mine, because vitamins are required for
life and were originally thought to be amines. Although not all vitamins are amines, they are
organic compounds required by humans in small amounts from the diet. An organic compound is
considered a vitamin if a lack of that compound in the diet results in overt symptoms of
deficiency.
Vitamin A
Vitamin A is a generic term for a large number of related compounds. Retinol (an alcohol) and
retinal (an aldehyde) are often referred to as preformed vitamin A. Retinal can be converted by
the body to retinoic acid, the form of vitamin A known to affect gene transcription. Retinol,
retinal, retinoic acid, and related compounds are known as retinoids. Beta-carotene and others
that can be converted by the body into retinol are referred to as provitamin A carotenoids.
Hundreds of different carotenoids are synthesized by plants, but only about 10% of them are
provitamin A carotenoids. The following discussion will focus mainly on preformed vitamin A
and retinoic acid.
Vitamin B6
Vitamin B6 is a water-soluble vitamin that was first isolated in the 1930s. There are three
traditionally considerd forms of vitamin B6: pyridoxal (PL), pyridoxine (PN), pyridoxamine
(PM). The phosphate ester derivative pyridoxal5'-phosphate (PLP) is the principal coenzyme
form and has the most importance in human metabolism.
PLP plays a vital role in the function of approximately 100 enzymes that catalyze essential
chemicalreactions in the human body. For example, PLP functions as a coenzyme for glycogen
phosphorylase, an enzyme that catalyzes the release of glucose from stored glycogen. Much of
the PLP in the human body is found in muscle bound to glycogen phosphorylase. PLP is also a
coenzyme for reactions used to generate glucose from amino acids, a process known as
gluconeogenesi s.
Vitamin BI2
Vitamin BI2 has the largest and most complex chemical structure of all the vitamins. it is unique
among vitamins in that it contains a metal ion, cobalt. For this reason cobalamin is the term used
to refer to compounds having vitamin BI2 activity. Methylcobalamin and 5-deoxyadenosyl
cobalamin are the forms of vitamin B12 used in the human body. The form of cobalamin used in
most supplen~entsc, yanocobalamin, is readily converted to 5-deoxyadenosyl and
methylcobalamin in the body. In manmals, cobalamin is a cofactor for only two enzymes,
methionine synthase and L-methylmalonyl-CoA mutase.
Vitamin C
Vitamin C, also known as ascorbic acid, is a water-soluble vitamin. Unlike most mammals,
humans do not have the ability to make their own vitamin C. Therefore, we must obtain vitamin
C through our diet.
Vitamin C is also a highly effective antioxidant. Even in small amounts vitamin C can protect
indispensable molecules in the body, such as proteins, lipids (fats), carbohydrates, anq nucleic
acids (DNA and RNA) from damage by free radicals and reactive oxygen species that can be
generated during normal metabolism as well as through exposure to toxins and pollutants (e.g.
smoking). Vitamin C may also be able to regenerate other antioxidants such as vitamin E.
Vitamin D
Vitamin D is a fat-soluble vitamin that is essential for maintaining normal calcium metabolism.
Vitamin D3 (cholecalciferol) can be synthesized by humans in the skin upon exposure to
ultraviolet-B (UVB) radiation from sunlight, or it can be obtained from the diet. Plants
synthesize ergosterol, which is converted to vitamin D2 (ergocalciferol) by ultraviolet light.
Vitamin D2 is less active in birds than vitamin D3 and may also be less active in humans. When
exposure to UVB radiation is insufficient for the synthesis of adequate amounts of vitamin D3 in
the skin, adequate intake of vitamin D from the diet is essential for health.
Vitamin E
The tem~vi tamin E describes a family of eight antioxidants: four tocopherols (alpha-, beta-,
gamma-, and delta-) and four tocotrienols (alpha-, beta-, gamma-, and delta-). Alpha-tocopherol
is the only form of vitamin E that is actively maintained in the human body; therefore, it is the
form of vitamin E found in the largest quantities in blood and tissues . Because alpha-tocopherol
is the form of vitamin E that appears to have the greatest nutritional significance, it will be the
primary topic of the following discussion. It is also the only form that meets the latest
Recommended Dietary Allowance (RDA) for vitamin E.
Vitamin K
Vitamin K is a fat-soluble vitamin. The "K" is derived from the German word "koagulation."
Coagulation refers to the process of blood clot formation. Vitamin K is essential for the
functioning of several proteins involved in blood clotting. There are two naturally occurring
forms of vitamin K. Plants synthesize phylloquinone, which is also known as vitamin KI.
Bacteria synthesize a range of vitamin K fom~uss ing repeating 5-carbon units in the side chain
of the molecule. These forms of vitamin K are designated menaquinone-n (MK-n), where n
stands for the number of 5-carbon units. MK-n are collectively referred to as vitamin K2. MK-4
is not produced in significant amounts by bacteria; instead, it appears to be synthesized by
animals (including humans) from phylloquinone. MK-4 is also formed from menadione, a
synthetic form of vitamin K present in animal feed. MK-4 is found in a number of organs other
than the liver at higher concentrations than phylloquinone. This fact, along with the existence of
a unique pathway for its synthesis, suggests that MK-4 has a unique biological function that has
not yet been identified.
Minerals
Minerals are elements that originate in the Earth and cannot be made by living organisms. Plants
obtain minerals from the soil, and most of the minerals in our diets come directly from plants or
indirectly from animal sources. Minerals may also be present in the water we drink, but this
varies with geographic locale. Minerals from plant sources may also vary from place to place,
because soil mineral content varies geographically.
Calcium
Calcium is the most common mineral in the human body. About 99% of the calcium
in the body is found in bones and teeth, while the other 1% is found in the blood and
soft tissue. Calcium levels in the blood and fluid surrounding the cells (extracellular
fluid) must be maintained within a very narrow concentration range for normal
physiological functioning. The physiological functions of calcium are so vital to
survival that the body will demineralize bone to maintain normal blood calcium levels
when calcium intake is inadequate. Thus, adequate dietary calcium is a critical factor
in maintaining a healthy skeleton.
Chromium
Although trivalent chromium is recognized as a nutritionally essential mineral, scientists are not
yet certain exactly how it functions in the body. The two most common forms of chromium are
trivalent chromium (111) and hexavalent chromium (VI). Chromium (111) is the principal form in
foods as well as the form utilized by the body. Chromium (VI) is derived from chromium (111) by
heating at alkaline pH and is used as a source of chromium for industrial purposes. It is a strong
irritant and is recognized as a carcinogenetic when inhaled. At low levels, chromium (VI) is
readily reduced to chromium (111) by reducing substances in foods and the acidic environment of
the stomach, which serve to prevent the ingestion of chromium (VI) .
Copper
Copper (Cu) is an essential trace element for humans and animals. In the body, copper shifts
between the cuprous (cul+) and cupric (cu2+) forms, though the majority of the body's copper is
in the cu2+ form. The ability of copper to easily accept and donate electrons explains its
important role in oxidation-reduction (redox) reactions and in scavenging free radicals.
Although Hippocrates is said to have prescribed copper compounds to treat diseases as early as
400 B.C., scientists are still uncovering new information regarding the functions of copper in the
human body.
Fluoride
Fluorine occurs naturally as the negatively charged ion, fluoride (F-). Fluoride is considered a
trace element because only small amounts are present in the body (about 2.6 grams in adults),
and because the daily requirement for maintaining dental health is only a few milligrams a day.
About 95% of the total body fluoride is found in bones and teeth. Although its role in the
prevention of dental caries (tooth decay) is well established, fluoride is not generally considered
an essential mineral element because humans do not require it for growth or to sustain life.
However, if one considers the prevention of chronic disease (dental caries) an important criterion
in determining essentiality, then fluoride might well be considered an essential trace element.
Iodine, a non-metallic trace elenlent, is required by humans for the synthesis of thyroid
hormones. Iodine deficiency is an important health problem throughout much of the world. Most
of the earth's iodine is found in oceans, and iodine content in the soil varies with region. The
older an exposed soil surface, the more likely the iodine has been leached away by erosion.
Mountainous regions, such as the Himalayas, the Andes, and the Alps, and flooded river valleys,
such as the Ganges, are among the most severely iodine-deficient areas in the world.
Iron
Iron has the longest and best described history among all the micronutrients. It is a key element
in the metabolism of almost all living organisms. In humans, iron is an essential component of
hundreds of proteins and enzymes .
Magnesium
Magnesium plays important roles in the structure and the function of the human body. The adult
human body contains about 25 grams of magnesium. Over 60% of all the magnesium in the body
is found in the skeleton, about 27% is found in muscle, 6% to 7% is found in other cells, and less
than 1% is found outside of cells.
Manganese
Manganese is a mineral element that is both nutritionally essential and potentially toxic. The
derivation of its name from the Greek word for magic remains appropriate because scientists are
still working to understand the diverse effects of manganese deficiency and manganese toxicity
in living organisms.
Molybdenum is an essential trace element for virtually all life forms. It functions as a cofactor
for a number of enzymes that catalyze important chemical transformations in the global carbon,
nitrogen, and sulfur cycles. Thus, molybdenum-dependent enzymes are not only required for
human health, but also for the health of our ecosystem.
Phosphorus
Phosphorus is an essential mineral that is required by every cell in the body for normal function.
The majority of the phosphorus in the body is found as phosphate (PO4). Approximately 85% of
the body's phosphorus is found in bone.
Potassium
Potassium is an essential dietary mineral and electrolyte. The term electrolyte refers to a
substance that dissociates into ions (charged particles) in solution, making it capable of
conducting electricity. Normal body function depends on tight regulation of potassium
concentrations both inside and outside of cells.
Sodium (Chloride)
Salt (sodium chloride) is essential for life. The tight regulation of the body's sodium and chloride
concentrations is so important that multiple mechanisms work in concert to control them.
Although scientists agree that a minimal amount of salt is required for survival, the health
implications of excess salt intake represent an area of continued investigation among scientists,
clinicians, and public health experts.
Zinc
Zinc is an essential trace element for all forms of life. The significance of zinc in human nutrition
and public health was recognized relatively recently. Clinical zinc deficiency in hunians was first
described in 1961, when the consumption of diets with low zinc bioavailability due to high
phytic acid content was associated with "adolescent nutritional dwarfism" in the Middle East.
Since then, zinc insufficiency has been recognized by a number of experts as an important public
health issue, especially in developing countries.
