The additive they found to be associated with heart disease is Vitamin C, so I'm somewhat skeptical of the value of these results given how well-studied it is.

I noticed that too. Its not the only one but what kinds of foods have ascorbic acid added as a preservative ?

Lowering the pH of food is a pretty common way to preserve it and if you're going to lower the pH then using an acid that is also a vitamin seems like an easy win.