1. Introduction
RS
Resonance Raman spectroscopy (RRS) has been used as a reference method for measuring skin carotenoid levels (SCL), which indicate vegetable and fruit intake. However, RRS is not an easy-to-use method in SCL measurement due to its complicated implementation. In this study, a commercial spectrophotometer based on reflection spectroscopy (RS), which is relatively simple and inexpensive, was evaluated to confirm usability compared with RRS in measuring SCL. To investigate the agreement between RS and RRS, eighty participants were randomly assigned to a high-carotenoid diet group (21 mg/day of total carotenoids) or a control-carotenoid diet group (14 mg/day of total carotenoids) during a 6-week whole-diet intervention period and a 4-week tracking period. Strong correlations between the RS and RRS methods were observed at baseline (r = 0.944) and the entire period (r = 0.930). The rate of SCL increase was similar during the diet intervention; however, the initiation of the SCL decrease in RS was slower than in RRS during the tracking period. To confirm the agreement of RS and RRS from various perspectives, new visualization tools and indices were additionally applied and confirmed the similar response patterns of the two methods. The results indicate that the proposed RS method could be an alternative to RRS in SCL measurements.Carotenoids are important indicators of vegetable and fruit (V & F) intake because they cannot be produced in the human body and must be obtained via external intake [Therefore, noninvasive methods of skin carotenoid level (SCL) measurement have been proposed to estimate V & F intake [Another noninvasive method, a relatively simple and implantable method known as reflectance spectroscopy (RS), has been employed to measure SCL. In the 1960s, predicting carotenoids in human skin using RS with wavelengths near 480 nm was suggested [In this study, we proposed the measurement of SCL by using a commercial spectrophotometer based on RS. To obtain a carotenoid-specific signal, wavelengths of the range related to carotenoids are selected by referring to the study by Ermakov and Gellermann [To verify a commercial RS-based spectrophotometer, a carotenoid diet intervention was performed in this study. Additional approaches were considered for evaluating RS as an alternative to RRS. The degree of agreement between two different measurement approaches has been conventionally evaluated as correlations or Bland–Altman plots [