Effect of Oral Carotenoid Therapy on Erythrocyte Protoporphyrin Levels

To the Editor.— Miao et al 1 reported that protoporphyrin levels in erythrocytes of patients with erythropoietic protoporphyria (EPP) were higher in winter than in summer and were elevated during administration of oral beta carotene. In developing a possible explanation for the protective effect of the carotenoid, they cited Piomelli et al 2 in support of statements that protoporphyrin leaks from erythrocytes of patients with EPP, and protoporphyrin is rapidly cleared from the plasma in vivo. Since this is not the first time Piomelli et al were cited about in vivo events in EPP, 3 a correction is in order. Despite use of the term "in vivo" in the title of the report, the study was an in vitro one. In fact, Scholnick et al 4 published information concerning in vivo turnover of plasma protoporphyrin. They administered tritiated δ-aminolevulinic acid (ALA- 3 H) and glycine labeled with radioactive carbon (glycine