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Hair and Nail Carbon Isotope Ratios Are Inversely Associated With Healthy Eating Index Scores and Fruit Intake in Adolescents
Abstract   Open access   Peer reviewed

Hair and Nail Carbon Isotope Ratios Are Inversely Associated With Healthy Eating Index Scores and Fruit Intake in Adolescents

Jessica J Johnson, Sarah H Nash, Diane M O'Brien and Gina L Tripicchio
Current developments in nutrition, Vol.10, 108333
07/2026
DOI: 10.1016/j.cdnut.2026.108333
url
https://doi.org/10.1016/j.cdnut.2026.108333View
Published (Version of record) Open Access

Abstract

Objectives: This study examines associations of carbon isotope ratios (CIR), measured from hair and nail, with dietary intakes and Healthy Eating Index 2020 scores in adolescents. Methods: Cross-sectional data from pilot studies conducted in adolescents (12–16.9 y) in Philadelphia, PA, USA were combined. Diet was measured using three interviewer-administered 24-hr recalls via the Automated Self-Administered 24-Hour (ASA24) platform. Average dietary intakes, including added sugar (g/d) and total fruit (cup eq./d), were calculated, along with Healthy Eating Index 2020 (HEI2020) scores. Scalp hair was collected to measure CIR, and nail was collected as an exploratory sample type. Spearman correlations identified associations between dietary variables and CIR biomarkers. Linear regression of HEI2020 scores and fruit intake (cup eq./d, Box Cox transformed) were performed on hair and nail CIR, with and without adjustment for participant characteristics. Results: The combined study sample ( n = 65) was 57% female, 71% Black/African American, 20% Hispanic/Latino, and had a mean age of 14.4 y (SD = 1.5). Analytical sample sizes were n = 57 for hair and n = 60 for nail. Hair CIR was inversely associated with total HEI2020 score ( ρ = −0.35, P = 0.008) and fruit intake ( ρ = −0.42, P = 0.001). Nail CIR had similar inverse associations (HEI2020: ρ = −0.29, P = 0.024; fruit intake: ρ = −0.37, P = 0.004). In linear models, unadjusted and adjusted results were consistent (adjusted results presented): higher HEI2020 was associated with lower hair CIR ( β CIR = −6.09, SE = 1.84, P = 0.002), as was higher fruit intake ( β CIR = −0.33, SE = 0.11, P = 0.003). Higher HEI2020 was also associated with lower nail CIR ( β CIR = −4.44, SE = 2.04, P = 0.034), as was higher fruit intake ( β CIR = −0.32, SE = 0.10, P = 0.002). There was no association between CIR and added sugar intake in hair ( ρ = 0.12, P = 0.386) or nail ( ρ = 0.14, P = 0.295). Conclusions: This study provides novel evidence that hair CIR is associated with total diet quality (HEI) and fruit intake. Additionally, these data provide novel insights from adolescents, and for nails as a promising sample type for CIR biomarker measurement. Findings suggest that CIR may have broader applications in capturing total diet quality, and this should be further explored.

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