Potential protective role of vitamin C in peripheral artery disease: A Mendelian randomization and NHANES analysis

Although numerous studies have investigated the associations between micronutrients and peripheral artery disease (PAD), most existing evidence is observational and limited by confounding and lack of causal inference. To address these gaps, we combined Mendelian randomization (MR) analysis using genetic data with supportive epidemiologic evidence from National Health and Nutrition Examination Survey (NHANES) to examine the relationships between micronutrient status and PAD risk. This study was conducted in 2 phases. First, we used genome-wide association study summary statistics to assess the causal effects of 15 circulating micronutrients on PAD risk through 2-sample MR. A bidirectional MR was also performed to explore the possibility of a reverse causal effect between PAD and potential candidate micronutrients. In the second phase, we analyzed data from 3 cycles of the NHANES (1999-2004). Logistic regression and restricted cubic spline models were used to examine the association between dietary intake of potential candidate micronutrients and PAD risk, adjusting for relevant covariates. MR analysis showed that higher genetically predicted vitamin C levels were significantly associated with a reduced risk of PAD (inverse-variance-weighted odds ratio (OR) = 0.509, 95% confidence interval (CI): 0.356-0.727; P <.001), with no evidence of reverse causality. In the NHANES analysis, lower dietary vitamin C intake was independently and nonlinearly associated with higher PAD risk (overall prevalence 7.9%), showing an L-shaped relationship with a threshold at 225.82 mg/day. Compared to the lowest quartile, PAD risk was lower in the second quartile (adjusted OR = 0.79; 95% CI: 0.64-0.98) and third quartile (adjusted OR = 0.94; 95% CI: 0.63-1.38). No significant interactions were found in the subgroup analysis. Both genetic evidence from MR and supportive observational evidence from NHANES suggest that vitamin C may play a protective role in the development of PAD.