Heart Disease 8. Cells that have not properly differentiated are more likely to undergo precancerous changes. Vitamin A, by maintaining healthy cell membranes, helps prevent invasion by disease-causing microorganisms. Vitamin A also stimulates immunity and is needed for formation of bone, protein, and growth hormone. The earliest deficiency sign is poor night vision .
Severe deficiencies causing blindness are extremely rare in Western societies.
Less severe deficiencies are more likely to occur with a variety of conditions causing malabsorption. A high incidence of vitamin A deficiency in people infected with the HIV virus has also been reported. People with hypothyroidism have impaired ability to convert beta-carotene to vitamin A, but the details of this relationship remain unclear. Whether the average person would benefit from vitamin A supplementation remains unclear. Three major malformations occurred in this study, but all could have happened in the absence of vitamin A supplementation.