Originally Posted by Brian

Hi Harper and welcome to the forum, Yes they can, if they are in the right environment, that means once whatever was causing them to damage is taken away, its a pretty slow process though but well worth the wait.
There is a lot you can to help this along, eg- B12, multi B, etc, i would follow Liza's advise, there is a great thread by David about Supplements and a mountain of other good info, good luck.
Brian