Skin Carotenoids as Biomarker for Vegetable and Fruit Intake: Validation of the Reflection‐Spectroscopy Based “Veggie Meter”

Abstract

Skin is a relatively stable storage medium for carotenoids; non‐invasive optical measurements of carotenoids in this tissue via Resonance Raman spectroscopy (RRS) serve as a non‐invasive biomarker for fruit and vegetable (F/V) intake. The RRS method has been validated with HPLC‐based measurements of carotenoid concentrations in serum and excised skin tissue samples and has been shown in feeding studies to respond to changes in F/V intake. An attractive alternative to RRS is based on reflection spectroscopy (RS), which requires less complex instrumentation and has an advantage in also measuring skin melanin and hemoglobin absorptions. Using a suitable algorithm, the latter can be taken into account in the RS‐based derivation of skin carotenoid levels. Furthermore, these levels can be quantified in optical density units, which directly correlate with the carotenoid concentrations encountered in the measured tissue volume. The objective of this study was to validate the RS method via comparison with the RRS method. We compared RS and RRS measurements in 5 diverse human subject cohorts of different age groups and ethnicities in community and clinical settings. These measurements included inter‐subject comparisons of carotenoid levels in 146 adults and children, tracking of carotenoid changes in response to dietary interventions in 29 adults, and an ongoing exploration of a potential correlation between skin and retinal carotenoid levels in adult patients with vision disorders. Depending on the particular study, correlation coefficients varied between R ~ 0.80 and 0.96, showing that the RS method provides a valid substitute for RRS in skin carotenoid measurements of all age groups. A compact, portable instrument configuration will be presented, which permits rapid non‐invasive measurement and tracking of F/V derived carotenoid levels. In its capacity as “Veggie Meter” it should be attractive for screening of large populations and the assessment of the effectiveness of F/V intake interventions. Support or Funding Information Support for this research was provided in part by the Paso del Norte Health Foundation and the USDA‐ARS.