By
Dr. Ananda S Prasad
In 1974 the Food
and Nutrition Board of the U.S. National Academy of Sciences
made a landmark decision, to declare zinc an essential nutrient
and establish recommended dietary allowances for humans.
Later, including
zinc in total parenteral nutrition fluids was made mandatory,
which undoubtedly saved many lives. Dietary zinc deficiency
is very prevalent in the developing world (affecting nearly
2 billion people) where mainly cereals are consumed by the
population. A meta-analysis of 33 prospective intervention
trials of zinc supplementation and its effects on children's
growth in many countries showed that zinc supplementation
alone had a statistically significant effect on linear growth
and body weight gain, indicating that other deficiencies that
may have been present were not responsible for growth retardation.
Zinc supplementation
has been shown to improve neuropsychological functions in
Chinese children with zinc deficiency. It reduces the incidence
and duration of acute and chronic diarrhea and acute lower
respiratory tract infections in children in developing countries,
resulting in decreased mortality. Zinc deficiency in pregnant
women causes:
- Abnormal labor
- Retarded fetal
growth
- Fetal abnormalities
The immunological
effects of zinc deficiency during the early 1960s were not
known, although I knew that patients with zinc deficiency
in the Middle East died of infection before the age of 25
(personal observation). It has now been shown that in people
with zinc deficiency:
- Activity of
serum thymulin (a thymus specific hormone involved in T
cell function) is decreased
- An imbalance
between T helper cell (Th1) and Th2 function develops
- Lytic activity
of natural killer cells and the percentage of precursors
of cytolytic T cells are decreased
Zinc deficiency
has now been recognized to be associated with many diseases--for
example:
- Malabsorption
syndrome
- Chronic liver
disease
- Chronic renal
disease
- Sickle cell
disease
- Diabetes
- Malignancy
- Other chronic
illnesses
In these conditions,
deficiencies of other micronutrients such as vitamins and
other trace elements may also be associated. It should be
emphasized that nutritional zinc deficiency in the developing
countries does not occur in isolation.
Recently the National
Institutes of Health's Eye Institute conducted a large double
blind clinical trial including 3,640 elderly participants,
which showed that antioxidants and zinc supplements delayed
progression of age related macular degeneration and reduced
the risk of loss of vision. Zinc deficiency is also common
in elderly people.
Zinc decreases
the copper burden in humans; as such it has been used effectively
to treat Wilson's disease. In therapeutic doses, zinc has
been shown to be beneficial in the treatment of:
- Hepatic encephalopathy
- Sickle cell
disease
- The common cold
More than 300 catalytically
active zinc metalloproteins and more than 2,000 zinc dependent
transcription factors involved in gene expression of various
proteins have been recognized.
The problem has
been known for 40 years and a solution is still outstanding.
Despite all the evidence, practically no attention has been
given by the world's organizations to the problem of zinc
deficiency. Growth retardation and increased susceptibility
to infectious and cognitive impairment are common in developing
countries where nutritional deficiency of zinc is also prevalent.
British
Medical Journal February 22, 2003;326:409-410 (Full Text
Article)