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.
Brittle, easily broken toenails have a variety of possible causes. There is often not one single cause, but rather a number of factors working together. Hypothyroidism: Along with weight gain and fatigue, brittle nails and hair are among the more notable symptoms of an underperforming thyroid gland.