I watched a BBC Horizons video about the nitrates they add to processed meats like cured sausages, bacon, lunch meats etc as a preservative.
For those who are not familiar with BBC Horizons, its a British science show that covers just about every scientific subject one can think of.. From the universe we live in to religion to eating habits, obesity, etc.
What they found was that nitrates are so bad for humans that they can actually calculate the shortening of your life expectancy by how much and how often you eat them. It didn't rise to the level of smoking or eating hydrogenated foods but it was close. If I remember correctly, it was something like 3 times a week = 7 years of your life or something astoundingly bad like that.