Although a large body of observational epidemiological evidence suggests that higher blood concentrations of β-carotene and other carotenoids obtained from foods are associated with a lower risk of several chronic diseases (see Dietary Reference Intakes for Vitamin C, Vitamin E, Selenium, and Carotenoids [IOM, 2000]), no evidence pointed to the need for a certain percentage of dietary vitamin A to come from provitamin A carotenoids to meet the vitamin A requirement. In view of the health benefits associated with consumption of fruits and vegetables, existing recommendations for increased consumption of carotenoid-rich fruits and vegetables are strongly supported (see IOM, 2000). Consumption of five servings of fruits and vegetables per day could provide 5.2 to 6 mg/day of provitamin A carotenoids (Lachance, 1997), which would contribute approximately 50 to 65 percent of the men’s RDA for vitamin A.
Excessive alcohol consumption results in a depletion of liver vitamin A stores (Leo and Lieber, 1985). Depletion is partly due to the reduced consumption of foods. Furthermore, mobilization of vitamin A out of the liver may be increased with excessive alcohol consumption (Lieber and Leo, 1986). Because alcohol intake has been shown to enhance the toxicity of vitamin A (Leo and Lieber, 1999) (see “Tolerable Upper Intake Levels”), individuals who consume alcohol may be distinctly susceptible to the adverse effects of vitamin A and any increased intake to meet one’s needs should be in the context of maintaining health.
A number of factors can influence the requirement for vitamin A, including iron status, the presence and severity of infection and parasites, the level of dietary fat, protein energy malnutrition, and the available sources for preformed vitamin A and provitamin A carotenoids.
Parasites and Infection. Malabsorption of vitamin A can occur with diarrhea and intestinal infestations (Jalal et al., 1998; Sivakumar and Reddy, 1972). Furthermore, the urinary excretion of vitamin A