[pinkmuffinere]

+1. Researchers in the field will have better insight, but the immediate confounding factor i think of:

People that eat more preservatives are likely eating more unhealthy food in general (microwave meals, shelf stable snack and cookies, etc). This group is probably not dominated by people that eat tons of canned beans, sauerkraut, or other things that are generally-healthy-but-have-preservatives. And of course we would expect health problems from large quantifies of those unhealthy-but-preserved foods.