It's hard to say in an individual case. Even with smokers, how can you really say with any certainty, that it was the smoking and not an independently malignant

It's hard to say in an individual case. Even with smokers, how can you really say with any certainty, that it was the smoking and not an independently malignant cell that was the seed for lung cancer? We have group statistics that say healthy diet, getting your vitamin D, etc. are associated with lower incidences of cancer. But on a human level, cancer is not like getting an e. coli infection, where we can point to contaminated food or something as a direct cause. So personally, I encourage my loved ones to eat well and live healthy and all that jazz. But if heaven forbid they come down with a major illness like cancer, I'd leave their life decisions out of it; as much as we can say with statistics, I don't want them to feel like that last unlucky coin flip was in any way their fault. TL;DR: I don't know, and people are probably going to downvote you for being insensitive.