In humans
Vitamins are classified as either
water-soluble,
meaning that they dissolve easily in water, or
fat-soluble vitamins,
which are absorbed through the
intestinal tract with the help of
lipids (fats). In
general, water-soluble vitamins are readily excreted from the body. Each vitamin
is typically used in multiple reactions and, therefore, most have multiple
functions.
In humans there are 13 vitamins: 4 fat-soluble (A, D, E and K) and 9
water-soluble (8 B vitamins and vitamin C).
| Vitamin generic descriptor name |
Vitamer
chemical name(s) |
Solub -ility |
Reco -mmended dietary allo -wances
(male, age 19�70) |
Deficiency disease |
Upper Intake Level
(UL/day) |
Over
-dose
disease |
|
Vitamin A |
Retinoids
(retinol,
retinoids
and
carotenoids) |
Fat |
900 �g |
Night-blindness and
Keratomalacia |
3,000 �g |
Hyper
-vitamin-osis A |
|
Vitamin B1 |
Thiamine |
Water |
1.2 mg |
Beriberi |
N/D |
? |
|
Vitamin B2 |
Riboflavin |
Water |
1.3 mg |
Ariboflavinosis |
N/D |
? |
| Vitamin B3 |
Niacin,
niacinamide |
Water |
16.0 mg |
Pellagra |
35.0 mg |
Liver
damage |
| Vitamin B5 |
Pantothenic
acid |
Water |
5.0 mg |
Paresthesia |
N/D |
? |
| Vitamin B6 |
Pyridoxine,
pyrido
-xamine,
pyridoxal |
Water |
1.3-1.7 mg |
Anaemia |
100 mg |
Impair
-ment
of
proprio
-ception, nerve
damage |
| Vitamin B7 |
Biotin |
Water |
30.0 �g |
Dermatitis,
enteritis |
N/D |
? |
| Vitamin B9 |
Folic
acid,
folinic
acid |
Water |
400 �g |
Deficiency during pregnancy is associated with
birth defects, such as
neural tube defects |
1,000 �g |
Refer to
deficiency
of
Vitamin B6 |
| Vitamin B12 |
Cyanoco
-balamin,
hydroxy
-cobalamin,
methyl
-cobalamin |
Water |
2.4 �g |
Megaloblastic
anaemia |
N/D |
? |
|
Vitamin C |
Ascorbic
acid |
Water |
90.0 mg |
Scurvy |
2,000 mg |
Refer to
Vitamin C megadosage |
|
Vitamin D |
Ergocal
-ciferol,
cholecal
-ciferol |
Fat |
5.0 �g-10 �g |
Rickets and
Osteomalacia |
50 �g |
Hyper
-vitaminosis
D |
|
Vitamin E |
Tocop
-herols,
toco
-trienols |
Fat |
15.0 mg |
Deficiency is very rare; mild
hemolytic anemia in newborn infants. |
1,000 mg |
? |
|
Vitamin K |
phyllo
-quinone,
mena
-quinones |
Fat |
120 �g |
Bleeding diathesis |
N/D |
? |
In nutrition and diseases
Vitamins are essential for the normal growth and development of a
multicellular organism. Using the genetic blueprint inherited from its parents,
a fetus begins to
develop, at the moment of conception, from the nutrients it absorbs. It requires
certain vitamins and minerals to be present at certain times. These nutrients
facilitate the chemical reactions that produce among other things,
skin,
bone, and
muscle. If
there is serious deficiency in one or more of these nutrients, a child may
develop a deficiency disease. Even minor deficiencies may cause permanent
damage.
For the most part, vitamins are obtained with food, but a few are obtained by
other means. For example, microorganisms in the intestine�commonly known as "gut
flora"�produce vitamin K and biotin, while one form of vitamin D is
synthesized in the skin
with the help of natural
ultraviolet in
sunlight.
Humans can produce some vitamins from precursors they consume. Examples include
vitamin A,
produced from
beta carotene, and niacin, from the
amino acid
tryptophan.
Once growth and development are completed, vitamins remain essential
nutrients for the healthy maintenance of the cells, tissues, and organs that
make up a multicellular organism; they also enable a multicellular life form to
efficiently use chemical energy provided by food it eats, and to help process
the proteins, carbohydrates, and fats required for respiration.
Deficiencies
Deficiencies of vitamins are classified as either primary or secondary. A
primary deficiency occurs when an organism does not get enough of the
vitamin in its food. A secondary deficiency may be due to an underlying
disorder that prevents or limits the absorption or use of the vitamin, due to a
�lifestyle factor�, such as smoking, excessive alcohol consumption, or the use
of medications that interfere with the absorption or use of the vitamin.
People who eat a varied diet are unlikely to develop a severe primary vitamin
deficiency. In contrast, restrictive diets have the potential to cause prolonged
vitamin deficits, which may result in often painful and potentially deadly
diseases.
Because human bodies do not store most vitamins, humans must consume them
regularly to avoid deficiency. Human bodily stores for different vitamins vary
widely; vitamins A, D, and B12 are stored in significant amounts in
the human body, mainly in the
liver,
and an adult human's diet may be deficient in vitamins A and B12 for
many months before developing a deficiency condition. Vitamin B3 is
not stored in the human body in significant amounts, so stores may only last a
couple of weeks.
Well-known human vitamin deficiencies involve thiamine (beriberi),
niacin (pellagra),
vitamin C (scurvy)
and vitamin D (rickets).
In much of the developed world, such deficiencies are rare; this is due to (1)
an adequate supply of food; and (2) the addition of vitamins and minerals to
common foods, often called fortification.
Recent lines of evidence also suggest a link between nutrition and mental
disorders, as evidenced by Lakhan & Vieira (2008).
Side effects and overdose
In large doses, some vitamins have documented side effects that tend to be
more severe with a larger dosage. The likelihood of consuming too much of any
vitamin from food is remote, but overdosing from vitamin supplementation does
occur. At high enough dosages some vitamins cause side effects such as
nausea,
diarrhea,
and
vomiting,
Overdosage via vitamin supplements can be a problem
| Vitamin |
Amount |
Problem |
| Vitamin A (Retinol) |
|
Hypervitaminosis A |
| Vitamin B1 (Thiamin) |
|
|
| Vitamin B2 (Riboflavin) |
|
|
| Vitamin B3 (Niacin) |
> 2 g/day |
Liver
damage
and
other problems |
| Vitamin B5 (Pantothenic
acid) |
|
|
| Vitamin B6 (Pyridoxine) |
> 100 mg/day |
Nerve damage |
| Vitamin B7 (Biotin) |
|
|
| Vitamin B9 (Folic
acid) |
|
|
|
Vitamin B12 (Cobalamine) |
|
|
| Vitamin C (Ascorbic
acid) |
|
|
| Vitamin D (alciferol) |
|
Hypervitaminosis D
Over-calcification of
the bones, organs, etc. |
| Vitamin E (Tocopherol) |
|
Possible heart problems |
|
Vitamin K (Phyllochinone) |
|
Increases coagulation in patients taking
warfarin. |
When side effects emerge, recovery is often accomplished by reducing the
dosage. The concentrations of vitamins an individual can tolerate vary widely,
and appear to be related to age and state of health.
In the United States, overdose exposure to all formulations of vitamins was
reported by 62,562 individuals in 2004 (nearly 80% of these exposures were in
children under the age of 6), leading to 53 "major" life-threatening outcomes
and 3 deaths�a
small number in comparison to the 19,250 people who died of unintentional
poisoning of all kinds in the U.S. in the same year (2004).
|
