Carotenoids in human blood and tissues.

The occurrence of carotenoid pigments in human blood and tissues has recently become an area of renewed interest due to the observed inverse relationship between consumption of carotenoid-rich fruits and vegetables and risk of certain cancers. This article reviews current knowledge of the kinds and concentrations of carotenoids in human plasma (or serum) and solid tissues. Most reports have focused on the hydrocarbon carotenoids (lycopene, alpha-carotene, and beta-carotene) with fewer dealing with the more polar xanthophyll pigments. The available literature indicates substantial interindividual heterogeneity with respect to blood levels of both total and individual carotenoids. Reports of solid tissue levels are few, but also indicate large variation, with adipose tissue and liver seemingly the major sites of deposition. The relationship between the types and concentrations of circulating carotenoids and those in solid tissues of the same individuals is not known, but preliminary investigations in our laboratory show considerable qualitative homology between the carotenoids in fasting serum and those in fatty tissue.