I was just reading up and this is a common runner's problem. Even a badge of honour. Toes hit the toebox, repeatedly. On the forum google returned, there is much joking about having one or two good nails left, along with instructions on how to use a small drill to relieve pressure and keep the nail bed from lifting off. (Some of these runners have nail-less toes, and we need nails to protect the toes.)
One podiatriast recommends -if you can believe it- soaking the feet in full-fat milk "in order that the nails absorb the calcium." To his credit, he does allow you need to increase your calcium intake.
*I'm not sure soaking quite qualifies as "intake" in this case.