Vitamin A and Immunity
The immune system protects the
body against infection and disease. It
is a complex and integrated system
of cells, tissues, and organs that have
specialized roles in defending against
foreign substances and pathogenic
microorganisms, including bacteria,
viruses, and fungi.
One of the earliest signs of vitamin A
deficiency is night blindness, which
can lead to permanent blindness
if left unaddressed. Vitamin A
deficiency also lowers your immune
function, thereby raising your risk
of complications from infectious
diseases.
It also contributes to Hormonal
imbalances, Infertility, Mood
disorders, Skin problems such as
eczema and acne, and Thyroid
dysfunction.
Strict vegans who avoid all animalbased foods and alcoholics are two
groups that tend to be more prone to
vitamin A deficiency than the general
population. Vitamin A-deficient
individuals are vulnerable to certain
infections, such as measles, malaria,
and diarrheal diseases.
Subclinical vitamin A deficiency
might increase risk of infection as
well. Infections can, in turn, lead to
vitamin A deficiency in a number
of different ways, for example, by
reducing food intake, impairing
vitamin absorption, increasing
vitamin excretion, interfering with
vitamin utilization, or increasing
metabolic requirements of vitamin A.
Consuming a well-rounded, nutrientdense diet, with plenty of vegetables
and healthy fats, will go a long
way toward warding off vitamin A
Experimental studies in animal
models, along with epidemiological
studies, have shown that vitamin A
deficiency leads to immunodeficiency
! and increases the risk of infectious
diseases. Vitamin A and its
deficiency and other serious nutrient metabolites play critical roles in both
innate and adaptive immunity.
imbalances.
Vitamin A Benefits Your Vision
Vitamin A is very important for
good vision. Lutein and zeaxanthin
are particularly crucial for preventing
age-related macular degeneration,
the most common cause of blindness
among the elderly. Vitamin A affects
vision primarily by regulating gene
expression, but in order for this to
occur, it must be activated in a twostep process, converting from retinol
to retinal, and finally to retinoic acid.
Retinal binds to a protein known
as opsin, forming a vitamin-protein
complex known as rhodopsin. Each
photon of light that enters our eye
and collides with rhodopsin causes
the retinal to change shape and
release itself from the complex.
This event then translates into an
electrical impulse that our optic
nerve transmits to our brain.
The brain synthesizes myriad such
electrical impulses at every moment
and interprets them as vision. While
the function of opsin is to help
generate visual images by binding
and releasing vitamin A, opsin can
only maintain its proper shape and
function when it is bound to zinc. In
addition, zinc supports the conversion
of retinol to retinal, the form of
vitamin A that binds to opsin.
In innate immunity, the skin and
mucosal cells of the eye and respiratory,
gastrointestinal, and genitourinary
tracts function as a barrier against
infections. Vitamin A helps to maintain
the structural and functional integrity
of these mucosal cells.
Thus, vitamin A deficiency
compromises the integrity of this first
line of defense, thereby increasing
susceptibility to some types of
infection, such as eye, respiratory,
gastrointestinal, and genitourinary
infections.
Vitamin A is also crucial to the
normal function of several types
of immune cells important in the
innate response, including natural
killer (NK) cells, macrophages, and
neutrophils. Moreover, vitamin A is
needed for proper function of cells
that mediate adaptive immunity,
su ch as T and B cells; thus, vitamin
A is necessary for the generation
of antibody responses to specific
antigens.
Kepha Nyanumba is a seasoned
Marketing Africa Magazine columnist
working as a Consultant Nutritionist
at AAR Healthcare Limited. You can
engage him on this or related matters
via mail: [email protected]
or follow him on twitter: knyanumba,
Blog: kephanyanumba.blogspot.com.