1 A diet low in calcium and vitamin D makes you more prone to bone loss. 2  Medication use. 3  Some medicines increase the risk of osteoporosis. 4  Activity level. 5  Lack of exercise or long-term bed rest can cause weak bones. 6  Smoking. 7  Cigarettes are bad for bones, and the heart, and lungs, too. 8  Drinking alcohol.
Fungus infections of the fingernails can also turn the nails brown or yellow. The texture usually also changes; nails often become very thick and may crack or peel. Nail fungus infections are more common in the toes than the fingers. They affect about 12 percent of Americans and may run in families.
Distal subungual onychomycosis (DSO) is the most common type of fungal nail infection. It is caused by the same fungi that cause most cases of athlete's foot (dermatophytes). DSO infects the skin under the end of the nail (nail bed) and in the nail. The infection starts at the end of the nail bed, and part of the nail often turns yellow or white. Pieces of skin and nail fragments (debris) build up under the nail. As the condition gets worse, the nail may crumble and split, and it may separate from the skin. A thickened nail and a large amount of debris under the nail may cause discomfort when wearing shoes. DSO can be a lifelong infection and hard to treat.