The effect of oral zinc supplementation on plasma levels of vitamin A and retinol-binding protein in cystic fibrosis.

Oral zinc supplementation with 100 mg zinc sulfate over an 8-week period 
in 36 patients with cystic fibrosis and 17 siblings did not 
affect the vitamin A transport system, as evidenced by an absence 
of consistent and significant quantitative changes in plasma levels of vitamin 
A, retinol-binding protein, and zinc, nor did the exogenous zinc appear 
to stimulate growth or exert any clinical benefit to the cystic 
fibrosis patients. The lack of response to zinc supplementation might be 
explained by the fact that the group of cystic fibrosis subjects 
studied was fairly healthy in regard to clinical status and certain 
blood parameters, including zinc. 