Validation of Noninvasive Cutaneous Carotenoid Measurements as Nutritional Biomarker Across Body Composition Groups

Carotenoids are plant-derived bioactive compounds with antioxidant properties and well-established roles in human health. Circulating carotenoid concentrations are widely used as an objective biomarker of fruit and vegetable intake; however, their assessment by high-performance liquid chromatography (HPLC) requires invasive sampling and laboratory infrastructure. Reflection spectroscopy-based devices, such as the Veggie Meter and Biozoom, offer rapid, noninvasive alternatives for assessing cutaneous carotenoids (CC), but their validity across different body composition profiles remains insufficiently characterized. In this study, plasma carotenoid concentrations quantified by HPLC were compared with CC measurements obtained using the Veggie Meter and Biozoom in 54 healthy women across three study visits (n = 151 observations). Associations between plasma and cutaneous carotenoids were evaluated using Spearman and partial correlation analyses with adjustment for body fat percentage and were further examined using linear mixed-effects models (LMMs) accounting for repeated measurements including body fat percentage and smoking status as covariates. Total plasma carotenoid concentrations were strongly correlated with CC values measured by Biozoom (r_s (151) = 0.697, p < 0.001) and Veggie Meter (r_s (151) = 0.650, p < 0.001). Provitamin A carotenoids exhibited the strongest associations, whereas lutein and lycopene showed weaker correlations. All associations remained statistically significant after adjusting for body fat percentage and smoking status. Both plasma and cutaneous carotenoid levels were inversely associated with BMI and obesity-related measures (all p < 0.0033, after Bonferroni correction for multiple comparisons). These findings support the use of reflection spectroscopy-based cutaneous carotenoid measurements as valid, noninvasive nutritional biomarkers of fruit and vegetable-derived carotenoid exposure. Such tools may facilitate dietary assessment and monitoring in nutrition research, clinical practice, and public health settings, provided that body composition is considered when interpreting results.