As a public health problem, deficiency of vitamin A occurs
when the habitual intake of bioavailable vitamin A
is too little to meet physiological needs under prevailing
conditions. Needs are increased during growth periods
and when frequent infections cause inefficient utilization
of the vitamin. Historical records and recent experience
document that improved dietary intake, even when
most vitamin A activity comes from provitamin A carotenoids,
can correct the problem, especially when such
diets contain adequate fat and the subjects are relieved
of heavy worm infestation. An epidemiologic evaluation
of the entire food chain, consisting of production, procurement,
processing, and consumption, provides the
framework for selecting suitable dietary approaches. These
approaches include homestead food production, centrally
or home-based fortified foods, and educational approaches
promoting dietary diversification and modification of
preparation practices to conserve the vitamin and render
it more bioavailable. Even agricultural approaches that
select and propagate germ plasma from varieties with
increased micronutrient density can be utilized, including,
in the future, genetic modifications to increase micronutrient
density of vegetable and staple crops. Usually
a mixture of intervention strategies will be most
effective, particularly when social marketing accompanies
efforts to increase consumer acceptance and compliance.
Where the ecological and economic context prohibits
dietary approaches, or where acute deficiency necessitates
an immediate therapeutic response, distribution of vitamin
A supplements is needed until suitable food-based
approaches become feasible