A new study reveals that vitamin C from fresh produce—not supplements—may help protect people with type 2 diabetes from heart disease, reshaping how we think about diet and chronic illness prevention.
Study: Association of low vitamin C concentrations and low consumption of fresh fruit and vegetables with cardiovascular disease in type 2 diabetes. Image Credit: Evan Lorne / Shutterstock
In a recent study in the journal BMC Nutrition, researchers in Italy investigated the associations between vitamin C concentrations, diet, and cardiovascular diseases (CVDs) in type 2 diabetes (T2D) patients. They conducted a cross-sectional observational study of 200 adult diabetic outpatients.
Study findings revealed an inverse relationship between vitamin C concentrations and CVD prevalence in the study cohort, with 12.2% of patients (24 participants, excluding three with missing data) observed to have vitamin C deficiencies (≤20 μmol/L, per laboratory thresholds). A strong direct relationship was also observed between fresh fruit and vegetable consumption and vitamin C levels.
Background
Cardiovascular diseases (CVDs) are a leading global cause of non-communicable human mortality, estimated to claim ~18 million lives annually (WHO). CVDs are especially prevalent in patients with preexisting chronic metabolic conditions, particularly excessive body mass index (BMI) and type 2 diabetes (T2D).
Decades of research, including multiyear follow-up studies, have revealed an intricate and closely linked association between diet and CVD risk, with dietary habits found to account for ~45% of all adult CVD-associated deaths in the United States (US). The role of micronutrients in maintaining human health and well-being cannot be understated. Vitamin C (ascorbic acid) is an essential micronutrient whose benefits include 1. acting as a co-factor in several metabolic processes, and 2. serving as a potent antioxidant.
T2D patients are known to be exposed to high concentrations of free radicals due to the condition causing unusually high lipid peroxidation and reactive oxygen species (ROS) generation. This high oxidative stress has, in turn, been linked to exacerbating CVD risk. While mechanistic studies have demonstrated the benefits of synthetic vitamin C supplements in reducing these risks, clinical studies on supplements have produced conflicting results, with some suggesting potential risks in diabetic populations.
About the Study
The present study investigates three main topics: 1. Vitamin C concentrations in T2D patients, 2. Associations between vitamin C concentrations and CVD prevalence, and 3. Correlating the consumption of natural vitamin C sources (fresh fruits and vegetables) with vitamin C levels and CVD prevalence.
The study comprised a cross-sectional observational investigation of diabetic clinic outpatients between September 2022 and March 2023. Study participants were recruited based on the following criteria: 1. Age (between 18 and 80 years), and 2. Clinically diagnosed T2D. Participants who reported vitamin C supplementation in the preceding six months and those with medical histories of pernicious anemia, ongoing pregnancy, and autoimmune gastritis were excluded from the study.
Study data collection included: 1. Venous blood sample collection following an overnight fast, 2. Patient medical history and demographic records, and 3. Patient-completed food frequency questionnaires.
Collected blood samples were subjected to the Jaffé rate-blanked and compensated assay for serum creatinine estimations, standard laboratory biochemical assays, and Friedewald’s equation for evaluating low-density lipoprotein (LDL) cholesterol concentrations. High-performance liquid chromatography (HPLC) was used to determine Hemoglobin A1c (HbA1c) values. The CKD Epidemiology Collaboration (CKD-EPI) equation was used to estimate patient-specific glomerular filtration rates (GFRs).
Plasma samples were stabilized with the reducing agent 1,4-Dithioerythritol (DTE) to prevent vitamin C degradation before reverse-phase HPLC analysis. Medical history data were used to record and adjust for diabetes duration, BMI, blood pressure/hypertension, and medication use.
The food frequency questionnaire was used to assess participants’ daily intake of fresh fruits and vegetables, with servings categorized into less than 1 serving daily, one serving, two to three servings, and more than three servings. Student’s t-tests and the Mann–Whitney test were used to evaluate differences in biochemical assay results. Differences between serving cohorts were assessed using analysis of variance (ANOVA) and chi-squared (χ²) tests. Multivariate logistic regression models were used to estimate the relative contributions of vitamin C and confounding variables to CVD prevalence.
Study Findings
After screening clinic outpatients, the study recruited 200 participants (33.5% women) to participate. Male participants were observed to have slightly lower BMI than their female counterparts (~1.4 kg/m²), with no differences in mean age (66.7 years).
Study findings revealed that 12.2% of included patients (excluding three with incomplete data) suffered from severe vitamin C deficiencies (≤20 μmol/L). Alarmingly, participants with established CVD complications demonstrated significantly lower vitamin C levels than their T2D counterparts without CVDs. Multivariable logistic regressions confirmed these findings, demonstrating vitamin C concentrations as an independent inverse predictor of CVD prevalence.
Encouragingly, vitamin C levels were strongly correlated with the number of fruits and vegetable servings consumed per day – “28.7 ± 14.8 μmol/L with less than one serving per day, 45.4 ± 17.9 μmol/L with one to two servings per day and 49.8 ± 19.2 μmol/L with more than two servings per day.” Notably, participants consuming three or more servings daily had the highest observed vitamin C concentrations, though the study did not directly compare dietary intake to synthetic supplements.
“...considering the results of studies suggesting that vitamin C supplementation may not have a protective effect on cardiovascular outcomes, together with our results and those of other studies, we suggest that the consumption of fresh fruit and vegetables should be preferred over vitamin C supplementation in patients with type 2 diabetes.”
Conclusions
The present study establishes the importance of fresh fruit and vegetable consumption in preventing CVD incidence, particularly for T2D patients. It highlights the association between diet-derived vitamin C and CVD outcomes, stressing that naturally obtained vitamin C from diet may offer a more reliable protective effect compared to supplements, based on the study’s observational findings.