Vitamin A and emphysema

For smokers or those exposed to second-hand smoke, research suggests that vitamin A can protect you against the effects and damage caused by smoking. Richard Baybutt, an associate professor of nutrition at Kansas State University, made a surprising discovery: a common carcinogen in cigarette smoke, benzo(a)pyrene, induces vitamin A deficiency. In some of his earlier research, Baybutt had shown that laboratory animals fed a vitamin A-deficient diet developed emphysema. His latest animal studies indicate that not only does the benzo(a)pyrene in cigarette smoke cause vitamin A deficiency, but that a diet rich in vitamin A can help counter this effect, thus greatly reducing emphysema.

http://www.ncbi.nlm.nih.gov/pubmed/10801913