Association between circulating vitamin C concentrations and risk of diabetes mellitus: dual evidence from NHANES database and Mendelian randomization analysis.

This study explores the link between circulating vitamin C levels and the risk of diabetes mellitus (DM) using data from the National Health and Nutrition Examination Survey (NHANES) for the cycles of 2003-2004, 2005-2006, and 2017-2018. Our analysis revealed a significant inverse relationship, showing that higher levels of vitamin C are associated with a reduced risk of DM. Specifically, higher vitamin C concentrations correlated with lower odds of DM, particularly at elevated quartile levels. Despite these findings, Mendelian randomization (MR) analysis did not establish a causal link between vitamin C and type 1 diabetes (T1DM). Additionally, previous MR studies found no causal relationship between vitamin C and type 2 diabetes (T2DM). These results suggest that while vitamin C levels are inversely associated with DM risk, this association may not be causal. Potential confounding factors or reverse causation could explain the observed relationship. The complexity of these interactions emphasizes the need for further research to clarify the biological mechanisms and assess how lifestyle or other metabolic factors might influence the relationship between vitamin C and diabetes.