A method is disclosed for analyzing keratinized tissue, particularly fingernails, of a subject to diagnose osteoporosis and bone fracture risk. A Raman spectrum of a sample of keratinized tissue is generated. Broad spectral background features of the spectrum are removed, preferably by using Fourier transform analysis. Peak heights of Raman features of interest, particularly the S—S bond of cystine, are measured. These peak height measurements are normalized using reference peak heights of Raman features that are invariant between normal and osteoporotic subjects, such as the CH2 bending peak.