Methods of diagnosing bone disease such as osteoporosis are provided. The methods comprise detecting changes in the physical or chemical structure of a keratinized tissue as correlates of disease. The methods include detecting changes in the hardness, modulus, or level of sulfur bonding, particularly the level of disulfide bonding, in a keratinized tissue sample such as nail, hair, or skin. Changes in these variables serve as diagnostic markers of bone diseases that are associated with changes in bone elasticity and bone density.