Poor dietary habits is most def the number one cause; foods high in sugar, sodium, fat, and not to mention processed foods.
My american people look at me like I'm alien, going to Costco or a supermarket with me, is an experience for them.
When i started taking interest in the ingredients list, came to realise just how lax the US is in it's restrictions on the toxics allowed in their foods and drinks.
Y'all eating food made in Chernobyl, pretty much. Added fact that most don't even bother to familiarise themselves with the ingredients, you're doing it (picking and choosing) blind-folded too.