Vitamin A deficiency: visual progression and impaired immunity
THE CONTEXT
Vitamin A deficiency is described as the most important preventable cause of blindness and also compromises immune function.
Progression of visual abnormalities
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The earliest sign is loss of sensitivity to green light.
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This is followed by impaired adaptation to dim light and then night blindness, meaning inability to see in the dark.
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More prolonged deficiency causes xerophthalmia, with keratinization of the cornea and blindness.
Interaction with infection
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Vitamin A contributes to differentiation of immune system cells. Even mild deficiency increases susceptibility to infectious diseases.
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Retinol-binding protein transports vitamin A in the bloodstream and is a negative acute phase protein: its synthesis decreases in response to infection.
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Reduced retinol-binding protein synthesis lowers circulating vitamin A, further impairing immune responses.