Biotin, which is vitamin B-7, is the only supplement proven to improve the health of brittle nails. Doctors recommend taking a dose of 2.5 milligrams of biotin daily. Over the course of 6 to 9 months, biotin has been shown to improve the thickness of nails by 25 percent.
When taken daily, a few preliminary studies suggest that 10 milligrams of orthosilicic acid and 10 to 30 milliliters of colloidal silicon also improve the health of brittle nails.
For people with healthy nails, supplements have not been shown to increase thickness. A medical study in 2007 showed that a sufficient intake of vitamins and minerals is important to nail health, but it was not able to prove that other supplements, such as keratin, collagen and gelatin, improve the thickness of normal nails.
Thin, brittle nails can be the result of fungus, nail polish and damage while working with the hands. Experts at WebMD recommend avoiding nail polish, which weakens the nails with regular use. In place of nail polish, nail shellac can be used, which helps to seal in moisture and protect the nail. To avoid nail fungus, personal tools can be brought to the salon. People should prevent the manicurist from pushing back the cuticles, which provides an entry point for fungus. To protect nails from damage while working in the garden or doing dishes, gloves can be worn.