causing dark nails but dark nails can be the result of vitamin B12 defciiency. Take vita B 12 supplements for some days and check whether the symptoms improve.
Sometimes dark nails can be contributed to circulatory problems, which will result in limited blood flow to your hands
, legs and heart. Your blood vessels become blocked which obstructs the natural blood flow.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.