Vitamin D refers to a group of fat-soluble compounds responsible for enhancing absorption of calcium and other minerals. The most important forms are vitamin D3, which is synthesized in skin exposed to sunlight, and vitamin D2, which can be obtained through diet and supplements. Insufficient vitamin D levels are defined as 50-100 nmol/L, while severe deficiency is less than 12.5 nmol/L.

1. Vitamin D refers to a group of fat-
soluble secosteroids responsible for enhancing
intestinal absorption
of calcium, iron, magnesium, phosphate and zinc.
In humans, the most important compounds in
this group are vitamin D3(also known
as cholecalciferol) and vitamin
D2 (ergocalciferol).Cholecalciferol and
ergocalciferol can be ingested from the diet and
from supplements. The body can also synthesize
vitamin D (specifically cholecalciferol) in the
skin, from cholesterol, when sun exposure is
adequate (hence its nickname, the "sunshine
vitamin").

7. Insufficient 50–100 nmol/L
(20–40 ng/mL)
Mild 25–50 nmol/L (10–
20 ng/mL)
Moderate 12.5–25.0 nmol/L
(5–10 ng/mL)
Severe < 12.5 nmol/L
(< 5 ng/mL)

9. Vitamin A deficiency (VAD) is a lack of vitamin A in
humans. It is common in poorer countries but rarely seen in
more developed countries. Nyctalopia(night blindness) is
one of the first signs of VAD. Xerophthalmia, keratomalacia,
and complete blindness can also occur since Vitamin A has a
major role in phototransduction.
Approximately 250,000 to 500,000 malnourished children in
the developing world go blind each year from a deficiency of
vitamin A, approximately half of whom die within a year of
becoming blind. The United Nations Special Session on
Children in 2002 set a goal of the elimination of VAD by
2010.
The prevalence of night blindness due to VAD is also high
among pregnant women in many developing countries. VAD
also contributes to maternal mortality and other poor
outcomes in pregnancy and lactation.

10. VAD also diminishes the ability to fight infections. In
countries where children are not immunized, infectious
diseases like measles have higher fatality rates. As
elucidated by Alfred Sommer, even mild, subclinical
deficiency can also be a problem, as it may increase
children's risk of developing respiratory and diarrheal
infections, decrease growth rate, slow bone
development, and decrease likelihood of survival from
serious illness.
VAD is estimated to affect approximately one third of
children under the age of five around the world. It is
estimated to claim the lives of 670,000 children under
five annually.Approximately 250,000–500,000 children in
developing countries become blind each year owing to
VAD, with the highest prevalence in Southeast Asia and
Africa. According to the World Health Organization
(WHO), VAD is under control in the United States, but,
in developing countries, VAD is a significant concern.

13. Its a medical condition in which the
eye fails to produce tears. It may be
caused by a deficiency in vitamin
A and is sometimes used to describe
that lack, although there may be other
causes.
Xerophthalmia caused by a severe
vitamin A deficiency is described by
pathologic dryness of the
conjunctiva and cornea.
The conjunctiva becomes dry, thick
and wrinkled. If untreated, it can lead
to corneal ulceration and ultimately
to blindness as a result of corneal
damage.

14. The resulting cornea becomes totally
opaque. Unfortunately, this is one of the
most common reasons for blindness
around the world, particularly in
developing countries.
Keratomalacia is an eye disorder that
results from Vitamin A deficiency.Vitamin
A is required to maintain specialized
epithelia (such as in the cornea
and conjunctiva).