Carotenoids, chronic disease prevention and dietary recommendations

Carotenoids are C-30, C-40 or C-50 terpenoids produced by a number of bacteria, fungi, and plants. In addition to acting as vitamin A precursors such as β-carotene, their dietary intake and blood plasma/serum and tissue levels have been associated in several epidemiological studies to the reduced incidence of chronic diseases, including the reduction of type 2 diabetes and other cardiometabolic diseases, as well as some types of cancer. Lutein and zeaxanthin also appear to play a role in the amelioration of age-related macular degeneration (AMD), the main cause of blindness in the elderly, and may be regarded as conditionally essential nutrients for the elderly. Furthermore, some studies have proposed that carotenoids may improve cognitive functions. Though the underlying mechanisms remain to be fully elucidated, it is perceived that direct antioxidant effects and protection from UV-light, as well as rather indirect effects, acting on transcription factors such as NF-кB, Nrf-2, and nuclear receptors such as RAR/RXR (retinoic acid receptor/retinoid X receptor), altering gene expression, all can play a role. Despite individual intervention trials suggesting negative effects of high doses of β-carotene on smokers, perhaps due to effects related to cytochrome enzyme activation, there is accumulating evidence that these colourful pigments indeed contribute to a healthy life and well-being. However, further research is warranted to better understand factors influencing variable inter-individual responses following carotenoid consumption and to establish more detailed recommendations regarding their dietary intake and toward establishing health claims.