Table 1.

Examples of adverse effects associated with dietary intake of vitamin A. Effects are a product of dose level and dose frequency

Vitamin A Intake: Level and Frequency	Potential Clinical Effects (Institute of Medicine, 2001)
Extremely high acute intake (Excessive consumption of supplements, or foods extremely high in vitamin A)	Severe toxicity or lethality, likely due to rapid changes in membranes (fluid and hemodynamics) and possibly inappropriate gene expression.
Very high acute intake	Teratogenicity, likely resulting from inappropriate gene expression.
Moderately high chronic intake	Organ damage affecting metabolism (e.g., liver damage), likely as a result of membrane damage and/or inappropriate gene expression and their sequelae – e.g., fibrosis, or altered immune/inflammatory functions.
Marginally high chronic intake	Weakened tissues (possible bone fragility).
Chronic insufficient intake	Impaired night vision, blindness, reduced reproductive performance, poor antibody response, decreased bone growth, and impaired maintenance of the surface lining (e.g., skin, intestinal tract).