Agriculture Reference
In-Depth Information
AbstRAct
Essential nutrients vary enormously in their body content and requirements. They
are each crucial for normal metabolism, they interact with one another, and they act
differently when metabolism is altered by either nutrient deficiencies or excesses or
by disease. Their deficiencies can also affect the metabolism of invading microor-
ganisms. In poverty, numerous nutrient deficiencies and numerous infections coexist
and are synergistic, forming a vicious spiral that leads to malnutrition. The most
common form of this, affecting about half the children living in poverty in the devel-
oping world, is chronic stunting. It is preventable. This chapter focuses on nutri-
ent deficiencies and their effects. Specific micronutrients, important to health, are
included: iron, zinc and vitamin A, which have deficiencies that together appear
to be responsible for nearly 20% or 2 million deaths a year in young children; folic
acid and vitamin B
12
, which also contribute to the ubiquitous problem of anemia;
and selenium, thiamin, and vitamin D as examples for which we have learned much
from history and geography. For each nutrient, advice is given on estimation of nutri-
ent status. For several nutrients, however, the tests available are not yet sufficiently
specific. Zinc is an example; we still have no reliable measure of its status for either
clinical use or population studies. Finally, the major problem of childhood malnutri-
tion is outlined. Our knowledge and understanding of nutrient metabolism is sparse,
but still progressing.
oveRvIew
Among other challenges, poverty means inadequate intakes of monotonous diets
of poor quality (imbalance of essential nutrients, excessive antinutrients or toxins).
One meal may be the only meal possible. If it is breast milk for a young infant, then
dietary quality is excellent for the first 6 months. However, in poverty in much of
the developing world, the meal may only be maize meal porridge for all age groups.
This represents poor quality, being deficient in several essential nutrients (e.g., lysine
and zinc) and rich in antinutrients (e.g., phytate). Poverty also dictates that meals are
often contaminated, especially when fed from a bottle to an infant.
The almost inevitable consequence is frequent infections and malnutrition. These
become a vicious spiral: Malnutrition reduces barriers and resistance to infections, and
the consequent increased severity and duration of infections exacerbates malnutrition.
What has this to do with micronutrient deficiencies? It is obvious to all that mal-
nourished children receive too little dietary energy and protein. However, not so
obvious are the needs for and roles of individual essential nutrients, including micro-
nutrients, the vitamins and essential trace elements (Geissler and Powers 2006).
When a diet is of good quality and adequate quantity and provided hygienically to
an individual in good health, then the risks of deficiencies or toxicities of micronutri-
ents are minimized. In the face of poverty, the risks of deficiency of many micronutri-
ents are enormous. However, our knowledge of the world population's micronutrient
status is poor, as is our diagnosis and management of individual deficiencies. This is,
among other reasons, because of:
