I would absolutely love a study to explain the hypersensitivities people have and to, I presume, end the debate. Unfortunately, the data out there is happy to state what nitrates and nitrites are, though I think they frequently mix them up, and typically jump on board the "shut up about nitrates hurting you" train. The links in the article mentioned by Pops, thanks Pops, really just state some issues about the chemical natures of nitrate/nitrite compounds and whether they will give you cancer and how veggies have lots of these compounds. None really address the issue of headaches.
The nitrate/nitrite nay-sayers will never give up the argument if their concerns aren't addressed, rather than simply saying "your wrong if you eat veggies". I mean no offense by that statement, but if you had a serious medical concern and you were given answers like that, you would likely get grumpy about your affliction being ignored. A similar example was the issue of autism being caused by children's vaccinnes; we can just say "you is crazy" (which did not work), but we can do meta-analysis to show there was not a significant link between the two, which seems to have helped peoples fears.
We need to find the real causes of the headaches, whether its preservatives as DaveOmak suggested, my suggestion about excessive nitrate/nitriting of meat by the major producers/distributers or another reason all together. Perhaps then we can find a solution to this issues that makes us all happy.
Finally, as an aside for Banman, if you ever find your "nitrate free" meat is pink, then they are tricking you. Nitrites make it pink and are using a trick such as sourcing their meat from parts of Canada where they don't have to list the nitrate or are using the fermented celery juice powder which has shloads of nitrites.