Stable Isotope Values in Human Dentine Collagen and Fingernails Reveal Age-Related and Socioeconomic Dietary Patterns...

In this study, we analyzed δ¹³C and δ¹⁵N values in dentine collagen (reflecting early-life diet) and fingernail keratin (reflecting recent diet) from 92 living adult individuals, having 75 individuals having paired dentine and fingernail samples available, across Brazilian regions with contrasting socioeconomic conditions. While the sample size was necessarily limited by the availability of paired tissues, it provides a unique dataset for assessing dietary change within the lifespan and its relationship to socioeconomic context.

Using Bayesian linear models and self-reported dietary intake questionnaires, we investigated the influence of age, geographic region, and socioeconomic status on isotopic composition.

We found significant regional and socioeconomic effects: individuals from high-Human Development Index (HDI) municipalities and those reporting greater sugar intake had elevated δ¹³C values, while frequent fish and seafood consumption was associated with higher δ¹⁵N. Notably, δ¹⁵N in dentine collagen declined with tooth age, suggesting a historical decrease in the δ¹⁵N of food sources, likely linked to increased reliance on synthetic fertilizers and nitrogen-fixing crops.

Both tissues show a consistent regional contrast: participants from the Southeast exhibit higher δ¹³C and lower δ¹⁵N than those from the Northeast, consistent with greater intake of C₄-derived, corn- and sugar-based processed foods ("supermarket diet"') and proportionally lower trophic-level protein in the Southeast, versus lower δ¹³C in the Northeast consistent with diets centered on C₃ staples (rice, beans, manioc) and more limited access to ultra-processed foods.