Digestion and Absorbtion of
vitamins
Cellular Biochemistry and
metabolism 1
CLS 331
Dr. Samah Kotb
Lecturer of Biochemistry
2015
DIGESTION
&
ABSORPTION
OF
VITAMINS &
MINERALS
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Objectives
In the end of the lecture, you should know
1. Definition of vitamins.
2. Digestion and absorption of vitamins and
minerals.
3. Some important definitions in metabolism
Vitamins are organic nutrients that are required
in small quantities for a variety of biochemical
functions and which generally cannot be
synthesized in the body and must be supplied by
the diet
DIGESTION & ABSORPTION OF
VITAMINS & MINERALS
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 Vitamins and minerals
are released from food
during digestion.
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The fat-soluble vitamins are
absorbed in the lipid micelles that
result from fat digestion.
 Water-soluble vitamins and most
mineral salts are absorbed from
the small intestine either by active
transport or by carrier-mediated
diffusion.
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Vitamin B12 absorption requires a
specific transport protein, intrinsic
factor.
 Calcium absorption is dependent
on vitamin D.
 Zinc absorption probably requires
a zinc-binding ligand secreted by
the exocrine pancreas.
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Vitamin
D
regulates
calcium
homeostasis and is required for the
intestinal absorption of calcium.
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Synthesis of the intracellular calcium binding
protein, calbindin, required for calcium
absorption, is induced by vitamin D, which
also affects the permeability of the mucosal
cells to calcium, an effect that is rapid and
independent of protein synthesis.
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Phytic acid (inositol hexaphosphate) in
cereals binds calcium in the intestinal lumen,
preventing its absorption.
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Other minerals, including zinc, are also
chelated by phytate.
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 High concentrations of fatty acids in the
intestinal lumen as a result of impaired fat
absorption
can also reduce calcium
absorption by forming insoluble calcium salts;
a high intake of oxalate can sometimes cause
deficiency.
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IRON ABSORPTION
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Iron Absorption
It is limited & strictly controlled but
is enhanced by vitamin C.
 Inorganic iron is accumulated in
intestinal mucosal cells bound to an
intracellular protein, ferritin. Once
the ferritin in the cell is saturated
with iron, no more can enter.
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Iron Absorption
The most effective compound is
vitamin C, and while intakes of
40–60 mg of vitamin C per day
are more than adequate to meet
requirements.
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Iron Absorption
An intake of 25–50 mg of vitamin
C per meal will enhance iron
absorption, especially when iron
salts are used to treat iron
deficiency anemia.
 fructose also
absorption.
enhance
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iron
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Iron Absorption
 Heme iron from meat is absorbed
separately and is considerably
more available than inorganic iron.
 However, the absorption of both
inorganic and heme iron is
impaired by calcium a glass of milk
with a meal significantly reduces
availability.
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body mass index (BMI)
The body mass index, defined
weight in kilograms divided
height in meters squared,
commonly used as a way
expressing relative obesity
height.
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as
by
is
of
to
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Basal metabolic rate (BMR)
Basal metabolic rate (BMR) is
the energy expenditure by the
body when at rest , but not
asleep,
under
controlled
conditions of thermal neutrality,
measured at about 12 hours
after the last meal, and
depends on weight, age, and
gender.
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Basal metabolic rate (BMR)
 Body weight affects BMR
because there is a greater
amount of active tissue in a
larger body.
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Basal metabolic rate (BMR)
 The decrease in BMR with
increasing age, even when body
weight remains constant, is due to
muscle tissue replacement by
adipose
tissue,
which
is
metabolically much less active.
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Basal metabolic rate (BMR)
 Similarly, women have a
significantly lower BMR than do
men of the same body weight
because women’s bodies have
proportionately more adipose
tissue than men.
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Basal metabolic rate (BMR)
 Undernutrition occurs in two
extreme forms: marasmus- a form
of severe malnutrition characterized
by energy deficiency in adults and
children and kwashiorkor is a form
of
severe
protein
-energy
malnutrition
characterized
by edema in children.
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Basal metabolic rate (BMR)
Overnutrition from excess energy
intake is associated with diseases
such as obesity, type 2 diabetes
mellitus, atherosclerosis, cancer,
and hypertension.
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