I do think there are things which are toxic in the environment, depriving yourself of things, such as vitamin D from sunlight, is another factor but I think a toxic lifestyle in the sense of being a chronic people pleaser etc. will no doubt do it too.
Its left field but theorists like Eric Fromm and the other Bionics theorists, they've all been out of vogue for a long time and some of it as a result of how it was presented reads like so much hocum but they had a good idea when they suggested that psychology and biological life where holistically linked.
In the movie lost horizon the guy in Shangrila talks about how people living lives of perpetual struggle attempting to please and placate others are committing slow motion suicide. Now he was talking about principles or precepts but I think taking the holistic ideas into account it could trigger physiological slow death too.
Its a hard thing to accept though because some people who are complete assholes and dont worry about being complete assholes, who've never lost a moments sleep or agonised for a minute about others, and who smoke and drink and bully seem invincible while good people who go all out to help others and take the world on their shoulders possibly refraining from all those things like smoking or drinking alcohol or doing drugs die off.
Its also hard to accept because its something which is difficult to change or overcome or correct, its not like dieting or exercise or whatever its much harder than that and because its so hard it can be a source of stress all by itself.