VITAMINS: Overview of Vitamins

Functions of vitamins
Source of vitamins
Required doses of vitamins
Classification of vitamins

Overview of Vitamins

Functions of vitamins

Although vitamins do NOT give the body energy, they are essential for life as they are used as helpers in the extraction of energy (coenzymes). Vitamins help regulate metabolism, help convert fat and carbohydrates into energy, and assist in forming bone and tissue.

Source of vitamins

With the exception of vitamin D, (which can be made within the skin), vitamins cannot be made in the body; they must be provided in the diet or in dietary supplements. Some are produced for us within the gut, by bacteria that live there. We will discuss the food sources that are naturally rich in each particular vitamin below.

Required doses of vitamins

Although vitamins are essential for life, we do not need a lot of them. In states of good health and a well-balanced diet, we can get the vitamins we need from the food we eat. In states of altered metabolism (including mental and physical stresses, and during or following an illness), though, we may need more amounts of vitamins as the body's natural processes of healing and repair cannot go forward unless we have enough-sometimes more-of the vitamins required.

The recommended dietary allowance (RDA):

There may be a misunderstanding of the meaning of RDA. RDA is not the recommended amount of vitamins to take daily. Rather, it represents the minimum amount required to prevent an overt, frank deficiency-in healthy people with good absorption and the ability to maintain normal nutritional status.

The RDA underestimates the requirements of an organism under stress. It is not a good guide for your nutritional or dietary intake. For vitamin C, for example, the RDA is 60 milligrams a day-just enough to prevent scurvy in a healthy sailor.

The Dietary Reference Intakes (DRIs)

These are a group that includes the following other nutrient measures:

RDAs
Adequate Intakes (AI)
Estimated Average Intakes (EAR)
Tolerable Upper Intakes (UL)

DRIs are slowly becoming the more accepted form for nutrient recommendations. Experts expect that DRIs will take the place of the RDAs in time.

The recommended dietary allowance (RDA) of vitamins and minerals

Compound	units	Adult	Adult	Children	Infants	Pregnant	Lactating+
		Males (25 + years)	Females (25 + years)	4-8 years	6-12 mos.
Biotin	mcg	30*	30*	12*	6*	30*	35*
Folate	mcg	400*	400*	200*	80*	600*	500*
Niacin	mg	16**	14**	8**	4*	18**	17**
Pantothenic	mg	5*	5*	3*	1.8*	6*	7*
Vitamin A	mcgRE*	1000	800	700	375	800	1300
Vitamin B1(Thiamine)	mg	1.2**	1.1**	0.6**	0.3*	1.4**	1.5**
Vitamin B2 (Riboflavin)	mg	1.3**	1.1**	0.6**	0.4*	1.4**	1.6**
Vitamin B6 (Pyridoxine)	mg	1.7**	1.5**	0.6**	0.3*	1.9**	2.0**
Vitamin B12	mcg	2.4**	2.4**	1.2**	0.5*	2.6**	2.8**
Vitamin C	mg	60	60	45	35	95	90
Vitamin D	mcg	(51-70y) 10* (71+y) 15*	(51-70y) 10* (71+y) 15*	(1-8y) 5*	5*	5*	5*
Vitamin E	mgalpha TE*	10	8	7	4	12	11
Vitamin K	mcg	80	65	30	10	65	65

g =grams
mg = milligrams (0.001 g)
mcg = micrograms (0.000001g)
IU = International Units
RE = Retinol Equivalent
Alpha TE = alpha Tocopherol equivalent
+ Generally the higher number was reported.
* AI (Adequate Intake) from the new Dietary Reference Intakes, 1997: Calcium, Phosphorus, Magnesium, Vitamin D, and Fluoride. Values have changed from previous RDA.
** RDA (Recommended Dietary Allowance) from the new Dietary Reference Intakes, 1997: Calcium, Phosphorus, Magnesium, Vitamin D, and Fluoride. Values have changed from previous RDA.

Note: remember that the dosage above is prophylactic i.e. it is the minimum that you require per day, to prevent serious deficiency. The therapeutic dose of the nutrient is usually increased considerably, but the toxicity level must be kept in mind.

Classification of vitamins

13 different vitamins divided into two types, water-soluble and fat-soluble.

A. Fat-soluble vitamins: Four vitamins; A, D, E, and K are known as the fat-soluble vitamins. They are digested and absorbed with the help of fats that are in the diet.

B. Water-soluble vitamins: they include the vitamin B group of several vitamins and vitamin C, or ascorbic acid. These water-soluble vitamins are not stored in the body for long. Good sources should be eaten every day.