GDF15 and gallstones: When restricting to nondiabetic individuals, genetically predicted GDF-15 levels showed an inverse but non-significant association with gallstone risk (OR = 0.82, 95% CI: 0.59, 1.13; p = 0.228) when it is below the turning point, while genetically predicted high levels of GDF-15 (above the turning point) showed a significant positive association with an increased risk of gallstones (OR = 1.28, 95% CI: 1.90, 1.43; p = 0.002).