Nerves, feet and hands

Long nerves fail at their far ends first, which is why a shortage reads as numbness, pins and needles, or burning in the feet and then the fingers. The problem is the myelin sheath and the fibre itself, so repair is slow and partial if it has run for years. Methylcobalamin is the form Japanese practice built around for exactly this, with laboratory work showing Schwann cells remyelinating a stripped nerve. This is the slowest win on the list and the one most worth the longest run.