chemicals & blood vessels
Susan -- Yeah -- gotta watch out for the nitrate & nitrites in preserved meats (lunch meats) -- they expand the blood vessels also (and, at least in my case, are cumulative). I have to regard a b-l-t as an occasional treat instead of a staple. The worst case I ever heard of in this area was years ago at a munitions factory where employees became addicted to work. It seems that they were absorbing minute amounts of nitroglycerine all the time they were at work (pre-OSHA), so their cardiac blood vessels became accustomed to being enlarged (nitroglycerine for angina, remember?). If they went on vacation (longer than a weekend off work), their blood vessels returned to "normal" giving them angina attacks. Scary *and* funny, but a lesson regarding environmental influences. Anything that can dilate blood vessels (nitrates, low pressure weather, etc.) can and does induce migraines. The fact that we take vaso-constrictors to stop them is why too much too frequently can cause bounce-back headaches. Also why it's not good to stop certain meds too suddenly.