Dr. Ammar W. Ashor Clinical Nutrition
Water-soluble vitamins
Vitamins: organic, essential nutrients required in small amounts by the body for
health. Vitamins regulate body processes that support growth and maintain life.
The vitamins fall naturally into two classes: fat-soluble and water-soluble.
Solubility determines many characteristics of vitamins. It determines how they
are absorbed into and transported around by the bloodstream, whether they can
be stored in the body, and how easily they are lost from the body.
The water-soluble vitamins are absorbed directly into the bloodstream, where
they travel freely. Most are not stored in tissues to any great extent; rather,
excesses are excreted in the urine. Thus, the risks of immediate toxicities are not
as great as for fat-soluble vitamins.
The water-soluble vitamins (B vitamins and vitamin C) act largely as
coenzymes—small molecules combined with a larger protein compound
(apoenzyme) to form an active enzyme that accelerates the interconversion of
chemical compounds. Coenzymes participate directly in chemical reactions;
when the reaction runs its course, coenzymes remain intact and participate in
further reactions.
Several of the B vitamins—thiamin, riboflavin, niacin, pantothenic acid, and
biotin—form part of the coenzymes that assist enzymes in the release of energy
from carbohydrate, fat, and protein. Other B vitamins play other indispensable
roles in metabolism. Vitamin B6 assists enzymes that metabolize amino acids.
Folate and vitamin B12 help red blood cells and the cells lining the GI tract to
multiply.
1
, Dr. Ammar W. Ashor Clinical Nutrition
Thiamin (Vitamin B1)
Thiamin is part of the coenzyme TPP (thiamin pyrophosphate) that assists in
energy metabolism. The TPP coenzyme participates in the conversion of pyruvate
to acetyl CoA. This step allows carbohydrate fuel to enter the TCA cycle and
produce much more ATP than during glycolysis. Moreover, thiamin occupies a
special site on the membranes of nerve cells. Consequently, nerve activity and
muscle activity in response to nerves depend heavily on thiamin.
Thiamin is found in many foodstuffs, including cereals, grains, beans and nuts. It
is often added to food (e.g. in cereals) in developed countries. The dietary
requirement depends on energy intake, more being required if the diet is high in
carbohydrates.
Following absorption, thiamin is found in all body tissues, the majority being in
the liver. Body stores are small and signs of deficiency quickly develop with
inadequate intake. There is no evidence that a high oral intake is dangerous but
ataxia has been reported after high parenteral therapy.
Thiamin deficiency
Inadequate thiamin intakes have been reported among the malnourished and
homeless people. Similarly, people who derive most of their energy from empty-
kcalorie foods and beverages risk thiamin deficiency.
Alcohol provides a good example of how empty-kcalories can lead to thiamin
deficiency. Alcohol contributes energy but provides few, if any, nutrients and
often displaces food. In addition, alcohol impairs thiamin absorption and
enhances thiamin excretion in the urine, doubling the risk of deficiency. An
estimated four out of five alcoholics are thiamin deficient, which damages the
brain’s structure and impairs its function.
2
Water-soluble vitamins
Vitamins: organic, essential nutrients required in small amounts by the body for
health. Vitamins regulate body processes that support growth and maintain life.
The vitamins fall naturally into two classes: fat-soluble and water-soluble.
Solubility determines many characteristics of vitamins. It determines how they
are absorbed into and transported around by the bloodstream, whether they can
be stored in the body, and how easily they are lost from the body.
The water-soluble vitamins are absorbed directly into the bloodstream, where
they travel freely. Most are not stored in tissues to any great extent; rather,
excesses are excreted in the urine. Thus, the risks of immediate toxicities are not
as great as for fat-soluble vitamins.
The water-soluble vitamins (B vitamins and vitamin C) act largely as
coenzymes—small molecules combined with a larger protein compound
(apoenzyme) to form an active enzyme that accelerates the interconversion of
chemical compounds. Coenzymes participate directly in chemical reactions;
when the reaction runs its course, coenzymes remain intact and participate in
further reactions.
Several of the B vitamins—thiamin, riboflavin, niacin, pantothenic acid, and
biotin—form part of the coenzymes that assist enzymes in the release of energy
from carbohydrate, fat, and protein. Other B vitamins play other indispensable
roles in metabolism. Vitamin B6 assists enzymes that metabolize amino acids.
Folate and vitamin B12 help red blood cells and the cells lining the GI tract to
multiply.
1
, Dr. Ammar W. Ashor Clinical Nutrition
Thiamin (Vitamin B1)
Thiamin is part of the coenzyme TPP (thiamin pyrophosphate) that assists in
energy metabolism. The TPP coenzyme participates in the conversion of pyruvate
to acetyl CoA. This step allows carbohydrate fuel to enter the TCA cycle and
produce much more ATP than during glycolysis. Moreover, thiamin occupies a
special site on the membranes of nerve cells. Consequently, nerve activity and
muscle activity in response to nerves depend heavily on thiamin.
Thiamin is found in many foodstuffs, including cereals, grains, beans and nuts. It
is often added to food (e.g. in cereals) in developed countries. The dietary
requirement depends on energy intake, more being required if the diet is high in
carbohydrates.
Following absorption, thiamin is found in all body tissues, the majority being in
the liver. Body stores are small and signs of deficiency quickly develop with
inadequate intake. There is no evidence that a high oral intake is dangerous but
ataxia has been reported after high parenteral therapy.
Thiamin deficiency
Inadequate thiamin intakes have been reported among the malnourished and
homeless people. Similarly, people who derive most of their energy from empty-
kcalorie foods and beverages risk thiamin deficiency.
Alcohol provides a good example of how empty-kcalories can lead to thiamin
deficiency. Alcohol contributes energy but provides few, if any, nutrients and
often displaces food. In addition, alcohol impairs thiamin absorption and
enhances thiamin excretion in the urine, doubling the risk of deficiency. An
estimated four out of five alcoholics are thiamin deficient, which damages the
brain’s structure and impairs its function.
2
