Vitamin A and immune response:
Vitamin A deficiency often occurs in the U.S. population which may exacerbate iron deficiency and reduce the immune response to infection. Retinol supplements have an upper limit recommendation of 3000 IU/day. Vitamin A supplements in particular have been shown to increase growth and birth weight in babies born to HIV infected pregnant women. It is important to avoid both deficiency and excess intake of vitamin A which may result in toxicity. (6)
Vitamin A and colon cancer:
Antioxidant vitamins A, C, and E were found to lower the recurrence rate of cancers of the colon. Individuals (n=255) with a history of colonic adenoma were randomized to receive treatment with either (1) vitamin A (30,000 IU per day), vitamin C (1 gram per day), and vitamin E (70 mg per day); (2) lactulose; or (3) placebo for an average of 18 months. At the end of the treatment period, adenoma recurrence had occurred in 5.7% of the antioxidant vitamin group compared to 14.7% in the lactulose group and 35.9% in the placebo group. (7)
