Vitamins

Weeks 7 and 8


Reading:UCSD Nutrition:Chapters 4-5
New Nutrition:Unit 2

1. Premise: Vitamins are 13 organic chemical molecules which are required for growth and development.

A. They are required in very small amounts (micro- to milligram).

B. They are not used as a major source of fuel, but are required for metabolism.

C. They can not, with few exceptions, be synthesized by the body They must be provided through the diet or by supplementation. Exceptions are the conversion of tryptophan (an essential amino acid) to niacin (Vitamin B3) and the conversion of a cholesterol derivative in the skin to Vitamin D by sunlight or ultra-violet radiation.

D. Deficiencies in any one of the vitamins leads to specific lesions, physiological dysfunctions, which can be reversed by adding the deficient vitamin to the diet.

E. They have been isolated from natural sources, their chemical structures determined, and synthesized. There is no difference in the biological activity of natural and synthetic vitamins

2. Premise: Vitamins are required for life processes.

A. There are two major groups of vitamins which are distinguished on the basis of their solubility in water or organic solvents:

  • Water soluble vitamins
    B1, B2, B3, B6, B12, C, biotin, folic acid, pantothenic acid
  • Fat soluble vitamins
    A, D, E, K

B. Different creatures have different vitamin requirements. Man, primates guinea pigs and bats require vitamin C. Some worms require carnitine.

C. Some concoctions and compounds have been claimed to have vitamin activity without substantial evidence (i.e., Vitamin B17, CoQ, para amino benzoic acid, rose hips, bee pollen, lemon grass extracts, etc.)

D. Most important evidence for essentiality is provided by a compound's required presence in the TPN bag.

3. Premise: At least one, and frequently several well characterized biochemical roles have been discovered for each vitamin. There is no "magic" about vitamins and how they work.

A. With the single exception of Vitamin C, all water soluble vitamins are biochemically transformed to become dissociable coenzymes or chemically bound prosthetic groups and function in coordination with specific proteins (apoenzyme) to enzymatically catalyze important metabolic reactions. Examples:

Dissociable coenzyme

Niacin (B3) AE AE AE Nicotinamide Adenine Dinucleotide (NAD+)
vitamin coenzyme

Coenzyme + Apoenzyme ' Active enzyme

Prosthetic group function

Biotin + Apoenzyme AE Biotin-Enzyme
inactive active

B. Vitamin C (reduced ascorbate) reacts directly as an oxidation/reduction coenzyme without being chemically modified Reduced ascorbate (AH2) ' Oxidized ascorbate (A) + 2e- + 2H+

C. The fat soluble vitamins after biochemical modification can act as either or both coenzymes or hormones. Examples:

Retinol AERetinalAERetinoic acid
Vitamin A visual pigmentdevelopmental hormone
Vitamin D AE AE AE dihydroxy-Vitamin D
hormonal form

D. Vitamin E, as Vitamin C, can act as a free radical scavenger without modification.

4. Premise: Different vitamins are required in different amounts.

A. The amount of a vitamin required per day , the U.S. Recommended Dietary Allowance (USRDA), is a "consensus number" agreed upon by a committee of the National Academy of Science and the National Research Council. It is that intake of a given vitamin which prevents deficiency symptoms of that vitamin in 97.5% of the population studied This value is based upon a variety of data including epidemiology of humans, direct measurement of the vitamin in serum, tissues, and urine of normal and deficient individuals, and isotopic tracer studies. Animal studies which can be more controlled and manipulated are also considered.

B. There is no evidence that any vitamin prevents a disease other than a deficiency condition

C. There is no evidence that mega doses (>10x USRDA) can cure a disease or enhance athletic performance. Niacin is sometimes used as a drug to lower serum cholesterol.

D. Under some conditions mega dosing of vitamins can be toxic. Examples include A, D, and B6.

5. Premise: Different foods have different vitamin profiles.

A. Vitamins are distributed quite differently among the various foods and food products we consume. Frequently foods are fortified to restore vitamins lost in preparation or to supplement the food's nutritional value. Examples: The fortification of white flour with thiamin, riboflavin, and niacin; milk with Vitamins A and D; many breakfast foods with "everything". Such products are sometimes targeted to specific populations. Under ideal circumstances all of the required vitamins can be obtained from the diet

B. Individuals on restricted diets such as low calorie, vegetarian, meat- and-potatoes, meatless, non-dairy, etc. must consider the strategy of taking adequate supplements which contain 100% of the USRDA of all of the vitamins to provide those nutrients not consumed in their foods.

C. The UCSD Nutrition Book tables should be consulted for the distribution of particular vitamins the various foods. Carefully read labels on packaged foods.

D. Pregnant women and their developing babies must be assured adequate vitamin supplements. Folic acid and B12 deficiency can lead to serious developmental problems.

6. Premise: Vitamins are only one of the six major categories of essential nutrients in the TPN bag and are no more nor less important than the others.


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