Hey salukigirl. It may very well be a defincency of some kind like the others said. And you mentioned stress. Stree can make your hair brittle. I don't know about making your nails brittle though. I know in the weeks leading up to my mom's death, my hair was thinning in the front and my hairdresser/aunt told me it was stress and anxiety. So I went to my doc and had blood tests done, they all came back fine and stress was exactly what was causing the hair loss.