I live far enough from the equator, and get little enough sunlight exposure, that I believe I was deficient. After I started supplementing I noticed my fingerna

I live far enough from the equator, and get little enough sunlight exposure, that I believe I was deficient. After I started supplementing I noticed my fingernails growing stronger. I didn't anticipate this happening so I didn't save samples for objective measurement, but I clearly remember that my fingernails would easily buckle if I pressed the ends against each other, and now they do not. The cost and risk is very low, so I think it's worth it for the stronger fingernails (useful as prying tools).