The intake of vitamin A provides humans with an important
nutrient for vision, growth, reproduction, cellular differentiation
and proliferation, and integrity of the immune system. Vitamin A
deficiency can result in visual or ocular malfunctions such as
night blindness and xerophthalmia (1) and can reduce immune
responsiveness (2), which can result in an increased incidence or
severity of respiratory infections, gastrointestinal infections (3),
and measles (4). Vitamin A can be obtained from food, either as
preformed vitamin A in animal products (eg, eggs and dairy
products) or as provitamin A carotenoids, mainly b-carotene in
plant products (eg, dark-green leafy vegetables and fruit).
Clinical and subclinical vitamin A deficiency is still a problem,
affecting 250 million schoolchildren worldwide (5, 6). To prevent
clinical vitamin A deficiency in developing countries, chemically
synthesized vitamin A supplements have been distributed periodically
to deficient populations (7–9). This has been shown to be an