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.
One common scenario is an object dropped on the tip of the toe or finger. Sometimes blunt-force trauma to a nail causes excessive bleeding beneath the nail that causes enough pressure to loosen the nail -- in some cases causing complete loss of the nail shortly after.