Organic Elemental Composition in Fingernail Plates Varies between Sexes and Changes with Increasing Age in Healthy Humans

Abstract

Background: Keratin, an α-helical fibrous protein, is the primary component of human nail plates. No data on age-related changes in healthy subjects are present. Objective: This study investigated whether keratin amount and composition, as indicated by organic elemental composition of fingernails, varies with aging and between sexes. Methods: Nail clippings from 225 healthy individuals (93 males, 132 females), aged 20–90 years, were analyzed for carbon (C), nitrogen (N), and sulfur (S) contents with an automatic elemental analyzer. C/N and N/S ratios were calculated. The C/N ratio is indicative of keratin composition, i.e. the ratio of α-amino acids and protein. The relationship of elemental composition with dietary intake was analyzed by standardized food record. Results: Females have in their nails more sulfur (p < 0.001) and less nitrogen (p = 0.001), and thereby, a lower N/S ratio than males, whereas their carbon content is not different. With aging, the carbon content increases (p < 0.01, both sexes) and the nitrogen content decreases (p = 0.05, females), both leading to an increased C/N ratio (p < 0.001). By contrast, the sulfur content and the N/S ratio do not change with aging (p > 0.05). The carbon content correlates positively with macronutrient intake in females. Nitrogen and sulfur contents are not related with dietary intake. Conclusions: Results suggest that the N/S ratio is indicative of sex differences and the C/N ratio of aging in healthy humans. The increasing carbon content with ongoing age could be explained by loss of inorganic material from the nails, followed by a subsequent increase of organic material. The increasing C/N ratio gives evidence that keratin composition changes towards a higher amount of α-amino acids with aging.

Analysis of human nails by laser-induced breakdown spectroscopy

“…Concentrations of C and Sr are equal within the experimental error in both groups. Dittmar et al 21 reported that carbon content in male and female subjects was not different, which is in accordance with our analysis. In 1988, Takagi et al detected 18 elements in human nails by argon inductively coupled plasma emission spectroscopy.…”

“…As the age increases, the overall carbon level in the fingernails increases, although there are slight fluctuations. This was also observed by Dittmar et al 21 They performed analysis on 225 individuals (93 males and 132 females). Takagi et al reported that Al concentration decreased with age, which is not exactly in accordance with our results.…”

“…18 It should be mentioned that a number of samples in the present work and their distribution is not enough for making a statistically meaningful analysis. Also, the number of samples in the present work differs from the number of samples in other authors' research 18,20,21 The limited number of samples tested in the present work (45 samples) and also the number of samples in the original works, ranging from 117 to 512, do not allow one to draw definite conclusions on systematic difference in elements' concentrations between different groups.…”

Nail Damage (Severe Onychodystrophy) Induced by Acrylate Glue: Scanning Electron Microscopy and Energy Dispersive X-Ray Investigations

“…3b), containing C (80.00%) as the dominant element, as well as O (12.99%), N (6.06%), Na (0.37%), Si (0.10%), S (0.21%), and Ca (0.27%). The concentration of Na was increased in the damaged nail, Al was absent (possibly correlated with the less hardening nail) [32], whereas the concentrations of Si and S were low. The diminished content of S in the injured nail may be explained by the action of chemical compounds that can cause the destruction of the nail, attacking the disulfide bridges, which are responsible for the stability of keratin nail matrix (fig.…”

Permeation studies of novel terbinafine formulations containing hydrophobins through human nails in vitro

“…Mean carbon content in the fingernails of healthy adults is 45% and increases with aging. Females have more sulfur and less nitrogen, but the sulfur content does not change with aging (Dittmar et al, 2008). Understanding the structure and properties of the nail plate is fundamental for the development of potent drugs, which can be used in the treatment of nail diseases.…”