Like the skin, the fingernails are a reflection of a person's state of health. Low levels of zinc and iron as well as thyroid problems can cause brittle nails. However, brittle nails are often a normal result of aging.
Update Date 6/19/2013
Updated by: Kevin Berman, MD, PhD, Atlanta Center for Dermatologic Disease, Atlanta, GA. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Bethanne Black, and the A.D.A.M. Editorial Team.