borderline significantp = 0.088
In the stratification by baseline vitamin D level, vitamin D3 supplementation was associated with reduced mortality in both the normal vitamin D subgroup (HR = 0.14, 95% CI: 0.04–0.52, p = 0.003) and the deficient vitamin D subgroup (HR = 0.47, 95% CI: 0.21–0.96, p = 0.047), with a borderline significant interaction between the two groups ( p = 0.088).