Fingernail Mineral Profiling as a Non‐Invasive Tool to Assess Dietary and Lifestyle Factors: Results From the Cross‐Sectional Fulda <scp>NutriNAIL</scp> Study

In the past, fingernail and toenail analyses were mainly used for toxicological investigations on heavy metals and only a few studies used mineral content as a biomarker for assessing lifestyle or dietary habits. The Fulda NutriNAIL study examined associations between lifestyle, dietary habits, supplement use, and fingernail mineral composition in 184 participants (18-81 years) from Fulda, Germany. Mineral concentrations were quantified via Inductively Coupled Plasma Mass Spectrometry (ICP-MS), and questionnaire data were analyzed for lifestyle correlations. Positive mineral-to-mineral correlations were observed between sodium (Na) and potassium (K) (r = 0.89), calcium (Ca) and magnesium (Mg) (r = 0.57), and iron (Fe) and cobalt (Co) (r = 0.66). We detected 21% higher selenium levels in the fingernails of selenium supplement users than for non-users. Omnivores showed higher Se levels than vegans and slightly higher levels than vegetarians and participants with thyroid disorders had significantly higher nail selenium levels. In addition, nail surface features were linked to specific mineral differences: potassium in brittle nails, reduced sodium and potassium in longitudinal ridges, and reduced chromium (Cr) in white spots. These findings demonstrate that fingernail mineral profiling is a non-invasive method for assessing lifestyle- and diet-related micronutrient status.