A diet rich in fruits and vegetables has long been encouraged for health promotion and chronic disease prevention in the United States and other countries, but dietary assessment of these foods for research and surveillance is difficult.
Traditional self-report methods are subject to measurement error, and biomarkers of intake are increasingly used in dietary research. To date, studies of fruit and vegetable intake have relied on invasive carotenoid analyses in plasma or serum by the use of HPLC (High Performance Chromatography). This approach is proven and has been linked with important health outcomes, including total mortality, but has some key disadvantages, especially cost of phlebotomy, sample processing/storage, sample analysis, and the necessity of venipuncture, which may introduce participation bias as some people are unwilling to give blood.
Carotenoids are powerful fat-soluble nutrients that can be distributed into the top layer of the skin; therefore, the skin is like a mirror that reflects the nutritional status of human body. Recent investigations have shown that the carotenoids could serve as biomarker substances for the entire antioxidant network of the human skin.
Optical methods are feasible noninvasive methods. The fluorescence efficiency of carotenoids is very low; they cannot be detected in the skin by any fluorescence analyses. Other optical methods such as resonance Raman spectroscopy, Raman microscopy, reflection spectroscopy, and skin color measurements could be applied for in vivo determination of carotenoids in mammalian skin. All noninvasive measurements of cutaneous carotenoids were performed on the easily accessible skin areas (i.e., palm, forearm, forehead, and back). A high reproducibility of the cutaneous carotenoid measurements has been obtained in vivo by the Raman spectroscopic measurements and by the reflection spectroscopic measurements.
Most of the results obtained noninvasively were correlated with the results obtained by HPLC analysis, demonstrating that noninvasive measurements of carotenoid antioxidant substances in human skin are feasible and reliable methods as the assessment of nutritional status in human body.