Most of the epidemiological evidence points to carote-noids being a very important class of phytochemicals. While some of the effects may be attributable to a diet high in fruits and vegetables, and an overall healthy lifestyle, the presence of specific carotenoids localized in different areas of the human body lend evidence to their overall importance in the human diet. As methods are developed to assess carotenoid levels noninvasively in humans, large-scale studies that determine carot-enoid levels in blood, skin, and the eye may lead to a better understanding of their importance in human health and disease prevention. Additional epidemiolo-gic studies to further strengthen the associations that have been observed in populations are needed.
It must be kept in mind that study design and statistical analyses vary across published work and no one study can give conclusive evidence. An integrated mul-tidisciplinary approach to study the functions and actions of carotenoids in the body is necessary to understand fully the role of carotenoids in health and disease prevention. This includes comparisons of carotenoids in whole fruits and vegetables and their effect on human health and well being. High fruit and vegetable intake is associated with a decreased risk of cancer, cardiovascular disease, diabetes, AMD, and osteoporosis. Removing any one class of phytochemicals from the intricate matrix of the whole plant may not give the same beneficial outcome in terms of human health. Considering that the average intake of fruits and vegetables is still less than that recommended by health professionals, programs that promote the consumption of more fruit and vegetables may be more effective at preventing disease in the long-term than using individual pharmacological carotenoid supplements.
A question that remains is whether or not carote-noids can be considered nutrients. A variety of phy-tochemicals contained in fruits and vegetables including carotenoids are assumed to be needed for optimal health and reduction of chronic disease risk, but have not been classified as nutrients. Indeed, in 2000, the Institute of Medicine was unable to recommend a daily reference intake for any carote-noid. Several factors have been defined that categorize substances as nutrients: substances that must be obtained from the diet because the body cannot synthesize the active form, and are used in the body for growth, maintenance, and tissue repair. In addition, to being classified as a nutrient, further studies must be done to determine the essentiality of the substance and its specific function in the body. Other criteria for defining a nutrient include concentration in specific tissues, consumption, and/ or supplementation resulting in tissue concentration increases and improved tissue function. Lastly, a daily established dosage needs to be defined and a biomarker identified to assess status.
A large body of observational studies suggests that high blood concentrations of carotenoids obtained from food are associated with chronic disease risk reduction. However, there is little other evidence of their specific role in the body. Lutein and zeaxanthin are the only carotenoids found in a specific tissue (the macular region of the retina) that seem to have a specific function. Providing lutein in the diet increases macular pigment in humans. Animal studies show that a diet low in lutein can deplete macular pigment, but the influence on the health of the eye is not yet well understood. To further our understanding, large randomized prospective intervention trials need to be conducted to explore the essentiality of lutein supplementation for reducing ocular disease risk in humans. Thus, to date, no one specific carotenoid has been classified as an essential nutrient.
See also: Antioxidants: Diet and Antioxidant Defense; Observational Studies; Intervention Studies. Bioavailability. Cancer: Epidemiology and Associations Between Diet and Cancer; Epidemiology of Lung Cancer; Effects on Nutritional Status. Carotenoids: Chemistry, Sources and Physiology. Coronary Heart Disease: Prevention. Fruits and Vegetables. Lycopenes and Related Compounds. Older People: Nutrition-Related Problems. Phytochemicals: Epidemiological Factors. Supplementation: Dietary Supplements.
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