Sodium nitrite is not really a preservative. It slightly suppress the growth of harmful bacteria, but is not very efficient. It is not as harmful as many think, and even could be very useful as antidot for cyanide poisoning. However, constant excess nitrite supply is not a healthy thing. The worst thing is that it is widely used just to keep termally processed meat in products like sausages, ham and boiled pork that have to be grey naturally to keep pink color. Just to make meat products look "good" on shelves, nothing more.