My peripheral neuropathy started as hot/tingling feet the day after cycling for about 2 hours. The neurologists I saw all claimed that that cycling does not cause PN. After lots of literature searching I found studies from a German group showing that strenuous exercise causes homocysteine and methylmalonic acid levels to rise substantially (in some athletes HCY went up by almost a factor of 3) and in people who are B12 deficient homocysteine levels are still elevated after 24 hours. In another study the same group showed that blood levels of B12 are even worse at indicating functional B12 status in athletes than in sedentary people, and that B12 metabolism is altered in people who exercise regularly. Unfortunately it took me a few months to find this info, and my PN deteriorated all that time. My PN definitely started to improve when I started taking B12 supplements, it is still improving and I am cycling again. My neurologists scoffed at me when I told them all this and they are now very surprised that my PN is improving. They had told me it would probably remain the same. If only they would read their own literature and were a little less full of themselves!! The absolutely huge paintings of academic neurologists in their academic finery hanging on the walls in the waiting room of the neuromuscular clinic tells it all. One young neurology registrar seem to believe me so perhaps there is hope.

Anyway, (ranting over), that might be why B12 is thought of as a sports supplement.

Martin