Physicians have traditionally used fingernails mainly for toxicologic testing purposes. The findings of the Fulda NutriNAIL study suggest that mineral profiles offer broader clinical insights, including information on dietary habits and the use of dietary supplements. These results indicate that fingernails may substantially expand the diagnostic toolkit published in BioFactors.

“There has been relatively little research on mineral content as a biomarker for assessing lifestyle and dietary patterns,” said Marc Birringer, PhD, from the Department of Nutritional, Food and Consumer Sciences, Fulda University of Applied Sciences, Fulda, Germany, who led the study. “We were able to show that fingernail analysis is a low-cost, noninvasive, and practical method for nutrition and prevention research.”

Keratin-rich structures, such as hair and fingernails, are particularly well suited to reflect the body’s mineral status. They accumulate minerals over extended periods and function as stable biological archives. The study examined the associations between lifestyle, dietary habits, supplement use, and fingernail mineral composition.

Study Design

The analysis included 184 adults aged 18-83 years. Fingernail samples were collected and analysed for 17 elements using inductively coupled plasma mass spectrometry, an extremely sensitive analytical technique that is considered the gold standard for trace element analysis because it allows precise measurements at extremely low concentrations.

In parallel, Birringer and colleagues collected questionnaire data on diet, comorbidities, supplement use, and lifestyle factors. In this cohort, 62% of the participants followed an omnivorous diet, 20% were vegetarians, and 11% were vegans. Overall, 75% of the participants reported using dietary supplements, and 78% of the participants were female.

The findings showed that fingernails serve as a robust archive of individual mineral exposure. Mineral concentrations within individuals remained largely stable over a period of 5.5 months, whereas substantial variability was observed between participants.

A particularly strong positive correlation was observed between sodium and potassium concentrations, showing parallel variation. This finding likely reflects intracellular Na⁺/K⁺ transport activity in keratinocytes.

Positive mineral-to-mineral correlations were observed between calcium and magnesium, calcium and phosphorus, and iron and cobalt. For the latter pair, the authors cautioned that contamination from stainless steel instruments could influence the results. However, these values are consistent with those reported in earlier biomonitoring studies.

This study also suggests the potential diagnostic relevance of certain nail changes. Participants with brittle nails had potassium levels approximately 30% lower than those without brittle fingernails. Longitudinal ridging was associated with reduced sodium and potassium levels. The authors considered these associations to be biologically plausible, given the close link between sodium, potassium, and cellular hydration.

Participants with white spots on their nails, known as leukonychia, also showed abnormal trace element levels. This characteristic was correlated with approximately 29% lower chromium levels than those in participants without leukonychia. However, the clinical significance of these findings remains uncertain and requires further investigation.

The strongest association was observed with selenium. The mean fingernail selenium concentration was 0.44 µg/g, consistent with values reported in other European cohorts.

Participants who reported selenium supplementation had selenium levels approximately 21% higher than those who did not use selenium-containing supplements. Diet-related differences were evident among individuals who did not use selenium supplements. Vegans had selenium levels approximately 11% lower than those of participants following an omnivorous diet, whereas pescatarians tended to have higher selenium levels, likely reflecting the high selenium content of fish.

Interestingly, selenium concentrations were more than 10% higher in participants with thyroid disorders. Although thyroid hormone levels were not measured, researchers suggested that dietary advice, such as increased fish intake or thyroid-specific metabolic factors, may have contributed to this effect.

Clinical Relevance

The results of the NutriNAIL study provide early evidence that fingernails can reliably reflect long-term mineral profiles. The measured values responded particularly clearly to dietary patterns, most notably selenium intake.

The ability to assess long-term trace element exposure using a noninvasive method enables a broad range of potential applications. These include nutritional medicine, care for individuals with thyroid disorders, assessment of chronic deficiencies, and the prevention of potentially toxic exposure associated with the use of dietary supplements.

This story was translated from Medscape’s German edition.