Lecture 6 Water-soluble vitamins

Pantothenic Acid and Biotin

- Both are coenzymes that are involved in energy metabolism. - Deficiencies are rare. - Biotin... * Bacteria in the large intestine synthesize biotin.

What happens if riboflavin is missing from the diet?

- Fatigued easily. - Inflamed tongue, sores on the edges of the lips. * But deficiency is very rare.

Folate deficiency

- Folate deficiency affects cells that rapidly divide. - When do we have rampant DNA synthesis? * During embryonic development. - During the first few weeks after conception, the "neural tube" forms in the human embryo. This tube eventually develops into the brains and spinal cord. * The two neural tube defects are: 1. Spina bifida: Tube fails to close properly. 2. Anencephaly: Infants born have much of their brain malformed or missing, they usually die shortly after birth.

Vitamin B-6 (continued)

- Given its importance in protein metabolism, it is suggested that dietary adequacy be based on protein intake. * Luckily, meat has plenty of B-6 - Unlike most b vitamins, megadoses of vitamin B-6 are toxic.

Digestion and absorption of water-soluble vitamins

- In the stomach, vitamins are released from protein complexes in food. (B-12 is quite different) - The vitamins are absorbed by the small intestine and delivered to the liver via the portal vein. - Vitamins are then released into the general blood circulation. (Liver keeps/stores B-12) - Excess water-soluble vitamins are eliminated through the kidneys in the urine.

Things to note

- Most water soluble vitamins are sensitive to heat. - Most water soluble vitamins have numerous functions.

Niacin (B3)

- Niacin is part of two enzymes that participate in at least 200 reactions, including those involved in the release of energy from macronutrients! - We can produce some small amounts of niacin using one of the amino acids. * The amino acid is tryptophan. The ratio is 60mg:1mg. Thus niacin must be supplied by the diet.

What happens if niacin is missing from the diet?

- Pellagra disease 1. Dementia 2. Dermatitis 3. Diarrhea 4. Death - Initially considered an infectious disease.

B-12 deficiency

- Pernicious Anemia - Some people have a genetic defect that reduces their ability to produce intrinsic factor. - Eventually, develop pernicious ("deadly") anemia. * This condition is characterized by nerve damage and megaloblastic RBCs.

B-12 deficiency (continued)

- Vegans need to be concerned about their intakes of vitamin B-12. - Even vegetarians who include egg and milk products in their diets (lactoovovegetarians) may not consume enough vitamin B-12 to meet their needs. **Adequate folate can mask B-12 deficiency making it harder to diagnose**

Antioxidant power (Vitamin C)

- Vitamin C acts as an antioxidant by donating electrons to radicals. - It is the water-soluble antioxidant. - Vitamin C also may donate electrons to another antioxidant, Vitamin E. Thus, vitamin C recycles vitamin E so that it can regain its antioxidant function. Vitamin C improves absorption of non-heme iron. - Heme-iron comes from animals. - Non-heme iron comes from plants.

Vitamin B-6

A coenzyme for >100 enzymes. In other words, it is VERY important! 1. Needed for amino acid metabolism. * Without vitamin B-6 all amino acids become essential. * Conversion of the amino acid, tryptophan to niacin. * Conversion of a toxic amino acid, homocysteine, to cysteine, a nonessential amino acid. 2. Required for synthesis of the heme in hemoglobin. - Hemoglobin - the oxygen carrying protein ion in our blood. 3. A few others

Vitamin B-12 (continued)

Before entering the small intestine, - Vitamin B-12 binds with "intrinsic factor" (IF), a compound produced by certain stomach cells. - Now the "vitamin B-12/intrinsic factor complex" reaches the "ileum" where the vitamin is absorbed. Once absorbed and transported to the liver via the portal vein, the liver removes about 50% of the vitamin for storage. - A healthy liver has enough vitamin B-12 reserves to last up to 5 years. Food Sources of Vitamin B-12 - Plants do not make vitamin B-12; - We rely almost entirely on animal foods to supply B-12

Functions of Vitamin C

Collagen Synthesis - Collagen is a fibrous protein that gives strength to connective tissue (bone, teeth, skin, tendons, blood vessels). Symptoms of scurvy (vit. C deficiency): - Petechiae (pinpoint hemorrhages in skin), skin bruises easily, gums swell and become spongy, bleeding gums, teeth looses and fall out, opening up of old scars and infection.

Folate

Folate is the name for a group of related compounds. - Folic acid is the synthetic form found in supplements and added to fortify foods. - In the body, cells convert all forms of folate to folate-coenzymes. Coenzymes participate in: - DNA metabolism. * folate-containing coenzymes are needed to synthesize DNA. - Amino acid metabolism. - Conversion of homocysteine to methionine.

Riboflavin (B2)

Major functions in the body - A coenzyme needed for macronutrient metabolism. Exposure to light causes the vitamin to break down rapidly. - Riboflavin-rich foods, (e,g, milk) should not be packaged or stored in clear glass containers. (30 minutes of UV light will destroy 30% of riboflavin)

Thiamin (B1)

Major functions in the body - A coenzyme needed for macronutrient metabolism. What happens if thiamin is missing from the diet? - The body stores very little thiamin, deficiency symptoms can occur within a few days of a thiamin-deficient diet. The thiamin-deficiency is called "beriberi". - Symptoms: weakness, memory loss, weight loss. Thiamin deficiency can also occur from alcoholism. - This happens because alcohol interferes with thiamin absorption. Can lead to permanent brain damage.

Vitamin B-12

Part of coenzymes that - Assist in DNA synthesis. - Homocysteine metabolism. - Maintaining the myelin sheaths that insulate parts of certain nerve cells. * Without vitamin B-12, segments of myelin sheath gradually undergo destruction that can lead to paralysis.

What other cells in the body rapidly divide?

Red blood cells (RBCs) <-- rapidly divide! - RBCs live for about 4 months. The bone marrow is constantly replacing old or -worn out RBCs. - Without folate, RBC precursor cells that reside in bone marrow enlarge, but they cannot divide normally, because they are unable to form new DNA. - The bone marrow releases abnormal RBCs called "megaloblasts" into the bloodstream. - "Megaloblastic anemia", is characterized by large, immature RBCs. Because they are abnormal in shape they do not carry the normal amounts of oxygen.

How we absorb vitamin B-12 is unique for a vitamin. How so?

The natural vitamin B-12 in food is bound to proteins that prevent its absorption. Hydrochloric acid and pepsin in the stomach release B-12 from protein. - (Synthetic vitamin B-12 in dietary supplements or fortified foods is not bound to proteins, so it does not need stomach acid and pepsin to release it from foods. Thus, synthetic vitamin B-12 is more readily absorbed than the natural form of the micronutrient).

B's and C

Water-soluble B-vitamins 1. Thiamin 2. Riboflavin 3. Niacin 4. B-6 5. Folate 6. B-12 7. Pantothenic 8. Biotin Other water-soluble vitamins 1. Vitamin C