Seventy-nine children (mean age, 3.5 years) living in an impoverished urban area in Brazil where vitamin A deficiency is prevalent were randomly assigned to receive, in double-blind fashion, a single dose of vitamin A (100,000 IU for children less than 12 months of age; 200,000 IU for older children) or placebo. One month after treatment, the proportion of children who had a new parasitic infestation was significantly lower in the vitamin A group than in the placebo group (20% vs. 31%; p < 0.05). The beneficial effect was due primarily to fewer Giardia lamblia infections.
Comment: Vitamin A plays a role in immune function and has been found to protect against various types of infection. The results of the present study indicate that maintaining adequate vitamin A status improves host defenses against parasitic infestations, particularly Giardia. It is of interest that vitamin A absorption is impaired in people with giardiasis. Thus, Giardia, like politicians, attempts to create conditions favorable to its survival.
Lima AAM et al. Effects of vitamin A supplementation on intestinal barrier function, growth, total parasitic, and specific Giardia spp infections in Brazilian children: a prospective randomized, double-blind, placebo-controlled trial. J Pediatr Gastroenterol Nutr. 2010;50:309–315.