What Is the Current Direction of the Research on Carotenoids and Human Health? An Overview of Registered Clinical Trials.

Carotenoids have been the object of numerous observational, pre-clinical and interventional studies focused on elucidating their potential impacts on human health. However, the large heterogeneity among the trials, in terms of study duration and characteristics of participants, makes any conclusion difficult to draw. The present study aimed to explore the current carotenoid research trends by analyzing the characteristics of the registered clinical trials. A total of 193 registered trials on ClinicalTrials.gov and ISRCTN were included in the revision. Eighty-three studies were performed with foods, one-hundred-five with food supplements, and five with both. Among the foods tested, tomatoes and tomato-based foods, and eggs were the most studied. Lutein, lycopene, and astaxanthin were the most carotenoids investigated. Regarding the goals, 52 trials were focused on studying carotenoids' bioavailability, and 140 studies investigated the effects of carotenoids on human health. The main topics included eye and cardiovascular health. Recently, the research has focused also on two new topics: cognitive function and carotenoid-gut microbiota interactions. However, the current research on carotenoids is still mostly focused on the bioavailability and metabolism of carotenoids from foods and food supplements. Within this context, the impacts/contributions of food technologies and the development of new carotenoid formulations are discussed. In addition, the research is still corroborating the previous findings on vision and cardiovascular health. Much attention has also been devoted to new research areas, such as the carotenoid-microbiota interactions, which could contribute to explaining the metabolism and the health effects of carotenoids; and the relation between carotenoids and cognitive function. However, for these topics the research is still only beginning, and further studies are need.