Vitamin C from fresh foods helps reduce the risk of heart disease in type 2 diabetes

Vitamin C from fresh foods helps reduce the risk of heart disease in type 2 diabetes

A new study shows that vitamin C from fresh produce – not supplements – may help protect people with type 2 diabetes from heart disease and change the way we think about diet and chronic disease prevention.

In a recent study published in the journalBMC nutritionResearchers in Italy examined the associations between vitamin C concentrations, diet and cardiovascular diseases (CVDs) in patients with type 2 diabetes (T2D). They conducted a cross-sectional observational study of 200 adult diabetic outpatients.

Study results showed 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) experiencing 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

Vitamin C deficiencies associated with metabolic markers: Patients with vitamin C deficiency (≤20 µmol/L) had significantly lower HDL cholesterol (40.7 vs. 50.5 mg/dL) and higher triglycerides (130.8 vs. 120.1 mg/dL), suggesting broader metabolic disruption.

Cardiovascular diseases (CVDs) are a leading global cause of non-communicable human mortality, estimated to claim ~18 million lives per year (WHO). CVDs are particularly prevalent in patients with pre-existing chronic metabolic diseases, particularly excessive body mass index (BMI) and type 2 diabetes (T2D).

Decades of research, including multi-year follow-up studies, have revealed a complicated and closely linked relationship between diet and CVD risk, with dietary habits accounting 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 as an effective antioxidant.

T2D patients are known to be exposed to high levels of free radicals due to the disease, which produces abnormally high levels of lipid peroxidation and reactive oxygen species (ROS). This high level of oxidative stress has, in turn, been linked to exacerbating the risk of CVD. While mechanistic studies have demonstrated the benefits of synthetic vitamin C supplements in reducing these risks, clinical trials of supplements have yielded conflicting results, with some suggesting potential risks in diabetic populations.

About the study

The present study examines three main topics: 1. Vitamin C concentrations in T2D patients, 2. Associations between Vitamin C concentrations and CVD prevalence, and 3. Correlation of consumption of the natural sources of Vitamin C (fresh fruits and vegetables) with Vitamin C levels and CVD prevalence.

The study included a cross-sectional observational survey of the outpatient diabetic clinic 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 previous six months and those with medical anemia, ongoing pregnancy, and autoimmune gastritis were excluded from the study.

Gender gap in vitamin C levels: Men had lower average vitamin C levels than women (45.1 versus 51.8 µmol/L), but deficiency rates were similar—a paradox that highlights potential gender or physiological factors.

Study data collection included: 1. Venous blood sample collection after an overnight fast, 2. Patient medical history and demographic records, and 3. Patient-controlled food frequency questionnaires.

Collected blood samples were subjected to the Jaffé velocities and compensated assay for serum creatinine estimates, standard laboratory biochemical assays, and Friedewald's equation for assessment of low-density lipoprotein (LDL) cholesterol concentrations. High-performance liquid chromatography (HPLC) was used to determine hemoglobin A1C (HbA1c) levels. 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 prior to reverse phase HPLC analysis. Medical history data were used to 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 divided into less than 1 serving daily, one serving, two to three servings, and more than three servings. Student's t-tests and Mann-Whitney test were used to evaluate differences in biochemical test results. Differences between serving cohorts were assessed using analysis of variance (ANOVA) and chi-square (χ²) tests. Multivariate logistic regression models were used to estimate the relative contributions of vitamin C and confounding variables to CVD prevalence.

Study results

No drug mix: Cholesterol-lowering treatments and diabetes medications showed no effect on vitamin C levels, raising concerns that combined therapies could mask or worsen the deficiencies.

After the outpatient clinics, the study recruited 200 participants (33.5% women) to participate. Male participants were observed to have a slightly lower BMI than their female counterparts (~1.4 kg/m²) with no differences in mean age (66.7 years).

Study results showed that 12.2% of enrolled patients (excluding three with incomplete data) suffered from severe vitamin C deficiencies (≤ 20 μmol/L). Alarmingly, participants with established CVD complications showed significantly lower vitamin C levels than their T2D counterparts without CVDs. Multivariable logistic regressions confirmed these results and showed vitamin C concentrations as an independent inverse predictor of CVD prevalence.

Encouragingly, vitamin C levels were highly correlated with the number of fruit 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 more to two servings per day, and 49.8 ± 19.2 μmol/L with more than two servings per day." Specifically, participants who consumed three or more servings daily had the highest observed vitamin C concentrations, although the study was not directly compared to synthetic supplements.

"Considering the results of studies indicating that vitamin C supplementation, together with our results and other studies, may not be protective on cardiovascular outcomes, we suggest that consumption of fresh fruits 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 the prevention of CVD incidence, particularly for T2D patients. It highlights the connection between dietary vitamin C and CVD results and emphasizes that naturally obtained dietary vitamin C may provide a more reliable protective effect compared to dietary supplements, based on the observational results of the study.

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