Vitamin A
or retinol is a fat-soluble vitamin.
It is very important for vision, immune system, skin and growth. It is only
present in animal fats while few carotenes in plant foods (especially
beta-carotene) act as pro-vitamin A and some part of these carotenes can be converted into
Vitamin A by lever.
Importance
for Health
Vitamin A
is especially important for vision. It is needed by retina to form retinal
pigments which prevents night blindness.
Retina of eye is necessary for both colour vision and low light.
It is also
important for skin as it reduces dryness of skin by the growth of
mucus-secreting cells and also down-regulate production of sebum. It can also
treat and reverse skin problems like photodamage (sun-damaged skin), cellulite
and striae (stretch marks).
Vitamin A
is also important for immune system. It is helpful in maintaining immune systems
including macrophages, neutrophils, lymphocytes etc.
Vitamin A
is beneficial for human growth hormone which
is important for growth of body cells.
It is also
necessary for production of blood cells.
Deficiency
Symptoms
·
Night
blindness is the earliest sign of Vitamin A deficiency. Persistent and severe
deficiency produces xerophthalmia (eye
dryness) due to atrophy of mucus-secreting cells which can lead to total blindness.
·
Lack
of immunity can lead to ear infection, urinary tract infection and several
other infections.
·
Dryness
of skin and acne.
·
Impairment
of growth of body cells including skeletal growth.
·
Enamel
hypoplasia (thinning and deficiency of teeth enamel).
·
Reproductive
problems in both males and females. In males, it is due to atrophy of testes
germinal epithelium while due to interruption of sexual cycle in females.
Daily Requirement
The
daily requirement of Vitamin A differs with age, sex and other factors. RDA
(recommended daily intake) for men between 19 and 70 years of age is 900 micro-grams
while for the women of same age is 700 micro-grams. Upper limit for both male
and female is 3000 micro-grams. RDA is slightly higher than minimum
requirement.
Vitamin
A is directly present in animal foods and indirectly in plant foods (as pro-vitamin
A carotenes). Foods with higher amount are given below. It is given as their
quantity per 100 grams and percentage according to RDA of men.
·
Liver
(beef, fish) > (6500 micro-grams, 722%)
·
Liver
(chicken) > (3296 micro-grams, 366%)
·
Carrot
> (835 micro-grams, 93%)
·
Sweet
Potato (raw) > (709 micro-grams, 89%)
·
Butter
> (684 micro-grams, 76%)
·
Spinach
> (469 micro-grams, 52%)
·
Pumpkin
> (400 micro-grams, 41%)
·
Cheddar
Cheese > (256 micro-grams, 29%)
·
Egg
> (140 micro-grams, 16%)
·
Apricot
> (96 micro-grams, 11%)
These
values are according to USDA.
Problems with Higher Intake
Vitamin
A can be dangerous if taken in amount greater than tolerable upper limit (3000
micro-grams for most men and women). The condition is known as Hypervitaminosis
A. Its symptoms include softening of skull bone, blurred vision, decreased
appetite, headache, drowsiness, nausea, hair loss etc.
This
condition can be treated by avoiding high intake of Vitamin A.
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