Inadequate Vitamin C Status in Prediabetes and Type 2 Diabetes Mellitus: Associations with Glycaemic Control, Obesity, and Smoking

Abstract

Vitamin C (ascorbate) is an essential micronutrient in humans, being required for a number of important biological functions via acting as an enzymatic cofactor and reducing agent. There is some evidence to suggest that people with type 2 diabetes mellitus (T2DM) have lower plasma vitamin C concentrations compared to those with normal glucose tolerance (NGT). The aim of this study was to investigate plasma vitamin C concentrations across the glycaemic spectrum and to explore correlations with indices of metabolic health. This is a cross-sectional observational pilot study in adults across the glycaemic spectrum from NGT to T2DM. Demographic and anthropometric data along with information on physical activity were collected and participants were asked to complete a four-day weighed food diary. Venous blood samples were collected and glycaemic indices, plasma vitamin C concentrations, hormone tests, lipid profiles, and high-sensitivity C-reactive protein (hs-CRP) were analysed. A total of 89 participants completed the study, including individuals with NGT (n = 35), prediabetes (n = 25), and T2DM managed by diet alone or on a regimen of Metformin only (n = 29). Plasma vitamin C concentrations were significantly lower in individuals with T2DM compared to those with NGT (41.2 µmol/L versus 57.4 µmol/L, p < 0.05) and a higher proportion of vitamin C deficiency (i.e. <11.0 µmol/L) was observed in both the prediabetes and T2DM groups. The results showed fasting glucose (p = 0.001), BMI (p = 0.001), smoking history (p = 0.003), and dietary vitamin C intake (p = 0.032) to be significant independent predictors of plasma vitamin C concentrations. In conclusion, these results suggest that adults with a history of smoking, prediabetes or T2DM, and/or obesity, have greater vitamin C requirements. Future research is required to investigate whether eating more vitamin C rich foods and/or taking vitamin C supplements may reduce the risk of progression to, and/or complications associated with, T2DM.

Food Sources and Potential Determinants of Dietary Vitamin C Intake in Chinese Adults: A Cross-Sectional Study

“…On the basis of the antioxidant property of vitamin C, increasing evidence indicates that vitamin C intake is essential for human health by reducing the risk of progression to cardiovascular disease, type 2 diabetes mellitus, or other diseases in which oxidative stress plays a pivotal role [ 1 , 19 ]. Understanding dietary vitamin C intake and the extent to which the intake does not meet the recommendations and the underlying influencing factors will be valuable for targeted interventions to assure adequate vitamin C intake.…”

Appropriate Handling, Processing and Analysis of Blood Samples Is Essential to Avoid Oxidation of Vitamin C to Dehydroascorbic Acid

“…Clinical samples which had been collected for vitamin C observational and interventional studies and which had had ascorbate analysis carried out in the presence and absence of the reducing agent TCEP were included in the current analysis. These studies included samples that were processed for ascorbate HPLC analysis prior to storage: prediabetes cohort ( n = 24, ACTRN12616000858493), colorectal cancer cohort ( n = 30, ACTRN12615001277538), community acquired pneumonia cohort ( n = 24) and haematological cancer cohort ( n = 6, HDEC16STH235), and critically ill surgical cohort ( n = 17) and septic shock cohort ( n = 24) [ 20 ]; or samples that were stored as frozen plasma: community cohort ( n = 20) [ 21 ], and normal glucose control cohort ( n = 32), prediabetes cohort ( n = 24), and type 2 diabetes mellitus cohort ( n = 30) [ 22 ]. All clinical samples were collected into EDTA anticoagulant tubes, processed at 4 °C, and stored at −80 °C prior to HPLC analysis.…”

Vitamin C and Immune Function

“…The adipose tissue is infiltrated by pro-inflammatory macrophages and T-cells, leading to the accumulation of pro-inflammatory cytokines such as interleukins and TNF-α [ 224 , 225 ]. A decrease in plasma vitamin C levels has been observed in studies of type 2 diabetes [ 18 , 226 ], and a major cause of increased need for vitamin C in type 2 diabetes is thought to be the high level of oxidative stress caused by hyperglycemia [ 10 , 227 , 228 ]. Inverse correlations have been reported between plasma vitamin C concentrations and the risk of diabetes, hemoglobin A1c concentrations (an index of glucose tolerance), fasting and postprandial blood glucose, and oxidative stress [ 219 , 229 , 230 , 231 , 232 ].…”