We recognize two forms of vitamin A
a) preformed
b) pro vitamin
a) Preformed- this is a form of vitamin A found in the body. It is also found in
animal tissue.We recognize three active forms of this vitamin A
collectively known as retinols - retinol
- retinal
- retinoic acid
b) Pro vitamin - This form of vitamin A is found in plants . It is not active form of
vitamin A and has to be converted to its active form retinol in the
body. We refer to pro vitamin as Carotenoids. The most studied form of
carotenoids is the yellow orange pigment Beta carotene. Another forms
of carotenoids are Licopene- which is important photochemical that has
been found to reduce risk of prostate cancer. It is more effective when
heated.
Vitamin A can be stored in the body in the liver.Functions of vitamin A
- For proper vision
- For epithelial cells- these cells lean all the external lining.and vitamin A is needed
for their proper function.
- It is important for mucus producing cells- if not enough vitamin A is consumed,
syndrom of dry eye- xerophtalmia can result. It is a condition marked by dryness of
cornea and eye membranes, and can lead to blindness.This condition is not reversible.
- It is important for proper immune function.- this function is related to its effect on
epithelial cells that are our first line of defense against pathogens.
- It is important for proper growth and development- for DNA synthesis
- For cells differentiation
- It decreases risk for certain cancers- this is due to its function on cell dividing
process and also due to increasing activity of immune system cells.It is effective in
prevention especially- skin, lung bladder and breast cancer
- Carotenoids are also effective Antioxidants by which they also act to reduce cancer
risk.
Antioxidants -binds with free radicals to neutralize them. Free radicals are high active
compounds that due to lack of electron in their outer shell are unstable.
In search for replacing this missing electron they disturb and damage
other molecules that as a result become also unstable. This chain reaction
can damage our tissues but can also damage DNA sequence and thus turn cell
into cancerous cells. Antioxidants prevent this proses by scavenging free
radicals by supplying them with the missing electron. We produce free
radicals in our body as a result of metabolic processes but we also
breathe it in oxygen, drink it in water and eat it with our food.
Food sources of vitamin A
-Dark green leafy and dark orange vegetable.
-Animals - liver, fish oil, milk, egg products
Requirements
RE- retinol equivalent
RE = 1 mg retinol = 5 IU (IU - international units)
For adults man - 1000 RE (5000IU)
woman- 800 RE (4000IU)
Deficiencies
Elderly, alcoholics, anybody with severe fat malabsorption
Toxicity
Vitamin A can be toxic in large quantities 6-10 x RDA
Vitamin D
It is sometimes called a vitamin and sometimes also prohormone (precursor of an
active hormone) because it can be produced by the body under certain conditions.
In the presence sunlight skin cells are capable of synthesizing sufficient amount of
vitamin D from a derivative of cholesterol. The prohormone whether obtained from the
diet or synthesized by sunlight it is converted to its active form by specific enzymes
in the liver and kidneys. The active form of vitamin D is called Calcitrol. 10 minute
exposure to sunlight is sufficient for person with light skin to synthesize enough
vitamin D. It may take 10x longer for person with dark skin.
Functions
-absorption of calcium and phosphorus
-regulates calcium deposition in bones
-increases reabsorption and decreases excretion of calcium by kidneys.
-can influence differentiation in some cancer cells-skin, bone and breast cancer cells.
- adequate vitamin D intake has been associated with reduced risk of developing breast,
colon and prostate cancer
-recent studies also show it controls growth of parathyroid gland, aids in the function
of immune system, contributes to insulin secretion.
Deficiencies
a) Rickets
b) Osteomalacia
Rickets- softening of bones. It results from inability to deposit calcium and phosphorus
into the bones due to vitamin D deficiency. This is in children.
Symptoms are- enlarged head joints and rib cage, deformed pelvis and bowed legs.
In US it is usually associated with fat malabsorption and is seen in children
suffering with cystic fibrosis.
Osteomalacia- soft bones-it is rickets in adults. It can cause fracture I the hip,
spine and other bones. It is more likely occur in people with kidney,
stomach, gallbladder and intestinal disease( especially if most of the
colon has been removed) and in cirrhosis of the liver. These diseases
affect metabolism and absorption of vitamin D.
Treatment- combination of sun exposure and vitamin D or calcitrol
Deficiency
-inadequate exposure to sun
-totally breast fed infants that are not adequately exposed to sunlight
-remember- vitamin D is not in milk found naturally- it is fortified thus it is lacking
in breast milk
Sources- Fatty fish and their oil,
- Fortified milk
- Ready to eat cereals- are fortified
RDA for vitamin D
- there is no RDA for vitamin D any more
- now we have recommendations based on adequate intake of vitamin D. These
recommendations are based on latest research.
- we have AI- adequate intake 0-50 years of age = 5 micrograms a day = 200 IU
50-70 = 10 microgram
Over 70 years - 15 micrograms
The different recommendation for age groups is what is different from RDA that has set
amount same for all age groups.
- Upper limit is about 2000IU do not exceed 5 x the recommended adequate intake .
It has been shoving toxicity especially in children. Calcium then deposits in tissue
and calcifies it.
Calcitrol works with parathyroid gland to maintain homeostasis of calcium in the
blood. When serum calcium in the blood drops down parathyroid gland releases parathyroid
hormone that stimulates synthesis of Calcitrol in the kidneys. The Calcitrol then
interacts with specific cells in the small intestine kidney and bone. In the small
intestine it will promote calcium absorption. In the bone it will promote resorption of
bone- decalcification of bone and release of its calcium into blood and in the kidney
Calcitrol and parathyroid hormone prevent loss of calcium via urine.
Vitamin E
It is a member of family of tocopherols
Primary functions
- Antioxidant- most active is alpha tocopherol
- Has function on nervous system
- Acts on immune system
- Protects against cataract
Besides vitamin E, we have other antioxidants in our bodya) Glutathione peroxidase- selenium containing enzyme that can destroy peroxides.
It acts in conjunction with vitamin E to reduce free radical
damage to cells.
b) Superoxide dismutase- Enzyme containing manganese,coper,zinc that destroy superoxide.
Sources
Wheat germ, plant oils, polyunsaturated fatty acids-corn oil, soy bean oil, sunflower
oil, margarine.
RDA for vitamin E
Man - 10 mg alpha tocopherols
Woman - 8 mg -\\B\\B\\B\\B\\B\\--
-New recommendation is set on 200 IU = 133 mg It is impossible to get this amount from
diet . For that reason,it is recommended to supplement vitamin E on daily basis.
Vitamin K
Vitamin K belongs to the family of compounds known as phylloquinone.
Function
- Blood clothing (K stands for coagulation from Danish spelling Koagulation)
Vitamin K contributes to synthesis of blood clothing factors such as prothrombin.
Sources
- it can be synthesized in the small intestine
- green leafy vegetable the darker the vegetable the more vitamin K Kale, spinach,
turnip, broccoli, green beans, peace.
Deficiencies
Malabsorption and long term use of antibiotics that disturb flora in small intestine
- It is not well stored and thus in case of deficient diet or prolonged use of
antibiotics deficiency can occur.
- Vitamin A can interfere with absorption
- Vitamin E acts as antagonist- decreases clothing
- Balance diet will support each other and prevent undesirable effects.
- There is not known toxicity of vitamin K
