Nail calcium and magnesium content in relation to age and bone mineral density

In view of the importance of calcium (Ca) and magnesium (Mg) as major bone components and nutrients controlling bone metabolism, and the ready availability of nail samples for analysis, clippings of fingernails and toenails were analyzed for Ca and Mg. The clippings were dissolved in nitric acid and analysis was done, using atomic absorption spectrophotometry, in 169 women and 115 men between 20 and 80 years of age. Fingernail Ca concentration in men decreased from 927 +/- 50 ppm (mean +/- SEM) in their twenties to 464 +/- 50 ppm in their eighties, with a significant negative correlation with age (r = -0.322; P < 0.0001) and such a negative correlation was also shown in the women (r = -0.269; P = 0.0004). Toenail Ca concentrations also decreased significantly with age in men (r = -0.534; P < 0.0001) and women (r = -0.224; P = 0.0016). Fingernail Mg concentration, in contrast, increased significantly with age in both men (r = 0.209; P = 0.0145) and women (r = 0.280; P < 0.0001), but toenail Mg failed to show significant changes with age in either men or women. Multiple stepwise regression analysis of age and lumbar bone mineral density (LBMD) on fingernail Ca concentration eliminated age before LBMD. In a separate group of 33 women in their sixties, a significant positive correlation was noted between fingernail Ca and LBMD (r = 0.544; P = 0.0016) and between toenail Ca and LBMD (r = 0.399; P = 0.0215). A negative correlation was also noted between fingernail Mg concentration and LBMD (r = -0.389; P = 0.0252). Nail mineral content may be utilized as one of the indicators of bone mineral metabolism.