Randomly realised that Luffy should be at high risk of getting gout, right? Obviously that's not something that'll be a thing in One Piece, and in-universe Chopper and Sanji would prevent that from happening anyway.
But now I wonder, both should-be-canon but also complete headcanon, what specific illnesses are Sanji and Chopper preventing the crew from developing day in and day out? Scurvy of course, but other than that?
Luffy has a diet that predisposes him to gout but no other risk factors, and I don’t know how that would work with a rubber body. His use of Gear 2 would likely increase his risk of stroking out and is likened in-universe to doping or steroid use, but I think with his power he’d be at more risk for having his body age like an overused rubber band. I also personally think he should stretch less when he’s cold, but that’s neither here nor there.
Zoro’s an alcoholic and Sanji would be on a fast track for all the issues related to a 17 pack a day smoking history (COPD, emphysema, lung/throat/mouth cancer, etc). Usopp literally gave himself a split personality and Robin’s struggled with suicidal ideation since childhood. As Brook ages he’d be prone to osteoarthritis, and he’s not exactly sane either.
Franky never should have survived his initial surgery and would have to work around infection in all his internal hardware, and I suppose his immune system rejecting his artificial organs. How his GI tract works will forever remain a mystery, but he canonically has a refrigerator where his intestines should be so digestion and hydration would be tricky. In all honesty, Luffy should be asking Franky how he poops.
Nami would likely have shoulder and hand issues after stabbing herself during AP. There are a lot of complex muscle groups there, and for shoulder especially I’m sure she hit bone. Her foot got impaled during Alabasta too, but that was post Chopper. Her illness from LG was analogous to something like Lime disease, which often leads to other chronic health issues.
Much like Luffy and Gear 2, I think Choppers use of Monster Point, especially before learning to control it would cause great stress to his body with the additional potential consequences of doing all his drug testing on himself.
Jinbe seems pretty healthy, but he did get hit with a couple magma fists during Marineford. There might be scarring that causes him some issues—in deep burns, sweat glands are destroyed amongst other things—and arthritis issues from a life spent fighting. But that counts for pretty much all the crew, tbh.