Vitamin A homeostasis endangered by environmental pollutants.

Normal vitamin A function depends on adequate stores of the vitamin, a finely regulated supply of the vitamin to target tissues, and an ability of cells to generate functionally active forms of the vitamin. Both endogenous and exogenous factors can adversely affect vitamin A homeostasis. Polyhalogenated aromatic hydrocarbons are ubiquitous environmental pollutants and cause severe disturbances in vitamin A metabolism, manifested by an accelerated metabolism and breakdown of vitamin A and its metabolites and a depletion of vitamin A from the body; this sequence of events accounts for the vitamin A deficiency-like symptoms associated with PHAH intoxication. The mechanism(s) responsible for these events most likely includes altered activities of enzymes that are either directly or indirectly involved in critical vitamin A metabolic pathways. Human populations that continue to be exposed to environmental pollutants, may accumulate critical levels of polyhalogenated aromatic hydrocarbons and will be at risk for inadequate vitamin A function as well as for other health impairments that have been difficult to link to any specific causes. Therefore, it is important to seriously evaluate the similarities in physiological disturbances across species that have become apparent in studies with wildlife inhabiting polluted environments similar to ours; the relevance to human health is evident.