Methods for assessing aspects of carotenoid bioavailability

Carotenoids are a group of C-40 isoprenoid-based molecules with >600 representatives in nature, of which approximately 30 are of importance within our daily diet. This class of phytochemicals has recently attracted much attention due to potential health beneficial effects associated with carotenoid consumption, including reduction of cardiovascular diseases, protection from age-related macular degeneration, various types of cancer, and perhaps, bone health. Therefore, an increasing number of studies have been carried out, focusing on carotenoid bioavailability from the diet, which is typically low, in the magnitude of 1-50%, successive metabolization and measuring carotenoid status. However, up to date, there is no clear consensus on how to measure carotenoid bioavailability and status. A number of methods have been developed to measure certain aspects of bioavailability, including in vitro studies assessing matrix release and micellarization, i.e. bioaccessibility, uptake or transport into cells simulating the human small intestine (e.g. Caco-2 cells), animal experiments, and also human studies. However, these techniques do not necessarily yield well-correlated results. In living beings, carotenoids may be determined in different tissues, including plasma, plasma triacyl-rich lipoprotein fraction reflecting newly absorbed carotenoids, or various target tissues where carotenoids do accumulate to some degree, including the retina, liver, or adipose tissue. Isotopic methods employing stable or radioactive labeled carotenoids have been developed to differentiate between endogenous and exogenous carotenoids and to estimate utilization from single meals. The relation between carotenoid intake, uptake, absorption, distribution, metabolization/excretion, and status demand a good understanding of the existing methods to assess these various aspects of bioavailability across different models.