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Fingernail Mineral Profiling as a Non-Invasive Tool to Assess Dietary and Lifestyle Factors: Results From the Cross-Sectional Fulda NutriNAIL Study

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This cross-sectional study from the Fulda NutriNAIL cohort in Germany measured the mineral composition of fingernail clippings from 184 adults by ICP-MS, examining associations between nail mineral concentrations and dietary patterns, supplement use, and lifestyle factors. The study found that selenium content in fingernails reflected dietary intake patterns: omnivores showed higher selenium levels than vegans, vegans showed slightly higher levels than vegetarians, and selenium supplement users had 21% higher fingernail selenium than non-users. Positive correlations were observed between sodium and potassium (r=0.89), calcium and magnesium (r=0.57), and iron and cobalt (r=0.66). The study demonstrates that fingernail mineral profiling can serve as a non-invasive method for assessing dietary and lifestyle-related micronutrient status.

Key numbers

  • Participants: 184 (77.7% female; mean age 38.51 years SD 18.82; 20% vegan, 20% vegetarian, 7% pescatarian, 62.5% omnivore); recruited Fulda, Germany, May 2024.
  • Fingernail mineral concentrations measured by ICP-TQ-ICP-MS (iCAP TQ-ICP-MS, Thermo Fisher; ashing in 5.8 mL quartz vial with 1 mL 25% nitric acid, 500 microL 16% HNO3, 150 microL 30% H2O2; certified reference material WEPAL-IPE-192).
  • Coefficient of variation (CV) between individuals: Se 20.5%, Na 35%, Mg 35%, chromium (Cr) 65%, nickel (Ni) 61.5%, Mo 143%, B 223%, Fe 175%; lowest for S (16.9%), P (39.4%).
  • Key between-mineral Spearman correlations: Na-K r=0.89 (p value not stated, positive); Ca-Mg r=0.57; Fe-Co r=0.66; Se-S r=0.36; Se-Zn r=0.29; Se-Cu r=0.29. Manganese showed modest correlations with Mo (r=0.58), Fe (r=0.51), and Cr (r=0.53).
  • Selenium by dietary pattern: omnivores 21% higher Se than vegans (95% CI did not include the reference category); vegans slightly higher than vegetarians. Selenium supplement users (n=20) had 21% higher nail Se than non-users (95% CI entirely above zero).
  • Nail structure associations: brittle nails (n=29) associated with lower K (-30.3%); longitudinal ridges (n=51) associated with lower Na (-22.4%); white spots (n=29) associated with lower Cr (-29.1%). These are exploratory findings.
  • Intra-individual variation: 11 subjects tracked over 5.5 months (fingernails collected every 2 weeks); highest intra-individual CV: Mo (78%), Ni (61.5%). Lowest: Mg (2.9%), S (2.9%), Zn (3.1%), P (5.3%).
  • Highest intra-individual CV elements are those known to be more sensitive to short-term exposure changes.

Methods (brief)

Cross-sectional design; IRB approved (Fulda University of Applied Sciences, EK240519-Birringer-end); DRKS00034566. Participants recruited May 2024 via social media, university intranet, posters, and newspaper. Nails clipped with stainless steel scissors; collected in small zipper plastic bags; labeled by QR code. Cleaned per IAEA protocol (adapted for hair/nails): sonicated in acetone, water rinse twice, acetone rinse twice, dried at 45 degrees C for 60 minutes in vacuum. Approximately 30 mg clippings digested in 5.8 mL quartz vial; measured by iCAP TQ-ICP-MS (Thermo Fisher) with auto-sampler ASX 280 (Teledyne). Elements measured: Li, B, Na, Mg, P, S, K, Ca, Cr, Mn, Mo, Fe, Co, Ni, Cu, Zn, Se. Spearman correlations and log(e)-relative differences with 95% CI for group comparisons. SPSS Statistics version 29 and R Studio. FFQ not validated before the study.

Evidence fitness

The NutriNAIL study provides data on fingernail mineral and trace element concentrations in a healthy German adult population and their associations with dietary patterns. It is relevant to the wiki as a biomonitoring methodology paper and as evidence that fingernail Se reflects dietary and supplemental selenium intake. The paper does not measure metals in food or personal care products. The associations between nail structure features (brittle nails, white spots) and chromium or potassium concentrations are preliminary exploratory findings from a small sub-group and should not be treated as established clinical correlates.

Limitations

Cross-sectional design; cannot establish causal direction. FFQ was not validated prior to the study. The 11-subject intra-individual tracking sub-cohort is small. Recruitment via social media may have produced a health-conscious, supplement-using sample (75% reported supplement use). The population is 77.7% female, limiting generalizability to males. No diseased control group; all participants were apparently healthy volunteers.

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