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Background: Skin carotenoid measurement by reflection spectroscopy (RS) offers a noninvasive biomarker of carotenoid intake, but feasibility, reliability, and validity are not established in infants., Objectives: In this study we aimed to determine the feasibility and reliability of 4-mo-old infant skin carotenoid score (SCS) measurement and its correlation with total carotenoid intake and plasma concentrations., Methods: SCSs were measured in a prospective, observational study with a modified, portable RS device at the index finger and heel of the foot in 4-mo-olds (n = 21). Infant plasma, human milk, and formula carotenoid concentrations were measured by HPLC-photodiode array, and carotenoid intake was estimated from 7-d food diaries corrected for actual milk carotenoid content. Mean SCS, time to acquire measurements, replicate intraclass correlations, and bivariate correlations between SCS, carotenoid intake, and plasma carotenoids were examined. Exploratory analyses of returning 6- (n = 12) and 8-mo-old (n = 9) infants were conducted., Results: Mean ± SD finger and heel SCSs in 4-, 6-, and 8-mo-olds were 92 ± 57 and 92 ± 51; 109 ± 41 and 119 ± 44; and 161 ± 89 and 197 ± 128 units, respectively. Replicate SCS measurements were reliable, with high intraclass correlation (≥0.70) of within-subject visit measurements. Finger SCSs in 4-mo-olds were correlated with carotenoid intake (ρ = 0.48, P = 0.0033), and finger and heel SCS were correlated with total plasma carotenoid concentrations (ρ = 0.71, P < 0.0001 and ρ = 0.57, P = 0.0006, respectively). Eight-mo-olds' finger and heel SCSs were correlated with total carotenoid intake (ρ = 0.73, P < 0.001; ρ = 0.58, P = 0.0014, respectively), whereas SCSs in 6-mo-olds, in transition from exclusive milk to complementary feeding, did not correlate with plasma carotenoid or dietary carotenoids, despite correlation between plasma and dietary carotenoid intake (ρ = 0.86, P = 0.0137). Mixed models suggest plasma total carotenoid concentration, age, carotenoid intake, and age × carotenoid intake, but not measurement site, are determinants of infant SCS., Conclusions: Infant skin carotenoids are feasibly and reliably measured by RS and may provide a biomarker of carotenoid intake in 4-mo-olds. This trial was registered at clinicaltrials.gov as NCT03996395., (© The Author(s) 2022. Published by Oxford University Press on behalf of the American Society for Nutrition.)

Carotenoids are orange, yellow, and red lipophilic pigments present in many fruit and vegetables, as well as other food groups. Some carotenoids contribute to vitamin A requirements. The consumption and blood concentrations of specific carotenoids have been associated with reduced risks of a number of chronic conditions. However, the interpretation of large, population-based observational and prospective clinical trials is often complicated by the many extrinsic and intrinsic factors that affect the physiologic response to carotenoids. Extrinsic factors affecting carotenoid bioavailability include food-based factors, such as co-consumed lipid, food processing, and molecular structure, as well as environmental factors, such as interactions with prescription drugs, smoking, or alcohol consumption. Intrinsic, physiologic factors associated with blood and tissue carotenoid concentrations include age, body composition, hormonal fluctuations, and variation in genes associated with carotenoid absorption and metabolism. To most effectively investigate carotenoid bioactivity and to utilize blood or tissue carotenoid concentrations as biomarkers of intake, investigators should either experimentally or statistically control for confounding variables affecting the bioavailability, tissue distribution, and metabolism of carotene and xanthophyll species. Although much remains to be investigated, recent advances have highlighted that lipid co-consumption, baseline vitamin A status, smoking, body mass and body fat distribution, and genetics are relevant covariates for interpreting blood serum or plasma carotenoid responses. These and other intrinsic and extrinsic factors are discussed, highlighting remaining gaps in knowledge and opportunities for future research. To provide context, we review the state of knowledge with regard to the prominent health effects of carotenoids.