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.
1 Compulsive washing of the hands or feet can also contribute to brittle nails. 2  Age: As we get older, our bodies become less able to retain moisture, which eventually causes our hair and nails to become brittle and easily damaged.