In addition to that, Sodium nitrite has been used in the curing of meats for ages. Sodium nitrite solutions are actually injected into meats such as hams, and rubbed onto porkbellies (for bacon). There were some hypotheses in the seventies that N-Nitrosamines may be produced in the stomach due to consumption of sodium nitrite, however these hypotheses have been proven incorrect in recent studies.
Further reading on the safety of Sodium Nitrite:
http://www.medem.com/MedLB/article_detaillb.cfm?article_ID=ZZZ80XEN0IC&sub_cat=380 (http://www.medem.com/MedLB/article_detaillb.cfm?article_ID=ZZZ80XEN0IC&sub_cat=380)
EDIT: I hope people do not get the wrong idea from the above post, I just wanted to present that sodium nitrite is used in the food industry (in small amounts). If you were to eat 10g of Sodium Nitrite crystals you could experience, methemoglobinemia, cyanosis, respiratory arrest and other adverse health conditions. I am not saying this stuff is non-toxic in any way, the NFPA health rating is 2 out of a possible four.
sorry for any confusion,
methyl_ethyl