Abnormal urinary loss of vitamin C in diabetes: prevalence and clinical characteristics of a vitamin C renal leak

A Systematized Review of the Relationship Between Obesity and Vitamin C Requirements

Obesity rates have increased globally in recent decades. Body weight is used as a modifiable factor in determining vitamin requirements. Accordingly, vitamin C requirements are volumetrically scaled from data for healthy weight males to other age- and sex-based categories. Likewise, it is possible that increases in body weight due to obesity may affect vitamin C needs. A systematized literature review was performed to summarize evidence on whether obesity affects vitamin C intake or status. The literature was also scanned for potential mechanisms for the relationship. Many observational studies showed that vitamin C status is lower in overweight and obese children and adults; this may be explained by lower vitamin C intakes. Nevertheless, a reanalysis of carefully conducted intervention studies has demonstrated a lower vitamin C status in participants who were overweight or obese when given the same dose of vitamin C as subjects of normal weight. Several mechanisms have been proposed to potentially explain why vitamin C status is lower in people with obesity: changes in vitamin C partitioning between lean and adipose tissue, volumetric dilution, metabolic alterations due to obesity, and gut microbial dysbiosis. Depletion-repletion or pharmacokinetic studies that include individuals of diverse body weights and ages would be helpful to further investigate whether obesity increases requirements for vitamin C. The current evidence base supports a lower vitamin C status in people who are overweight or obese; however, the association may be attenuated by lower vitamin C intakes.

Vitamin C - a scoping review for Nordic Nutrition Recommendations 2023

Vitamin C has multiple metabolic functions in the body, but the available information on the exact relationship between these functions and the intake necessary to maintain them is very limited. However, most attempts to objectively measure adequacy of vitamin C status, including, for example, replacement of metabolic turnover, chronic disease prevention, urinary excretion, and saturation of immune cells and body compartment, currently point toward 50 µmol/L as a reasonable target plasma concentration. As a strong correlation between body weight and vitamin C status exists, recommended intakes (RIs) for other age groups may be extrapolated from the adult RI based on weight. However, as body weights above 70 kg are becoming increasingly common - also in the Nordic region - an RI of 140 mg/day for individuals weighing 100 kg or more should be considered to compensate for the larger volume of distribution. Finally, smoking continues to be a common contributor to poor vitamin C status; therefore, it is proposed that people who smoke increase their daily vitamin C intake by 40 mg/day to compensate for the increased metabolic turnover induced by smoking.

Estimating Vitamin C Intake Requirements in Diabetes Mellitus: Analysis of NHANES 2017-2018 and EPIC-Norfolk Cohorts

Vitamin C is an essential enzyme cofactor and antioxidant with pleiotropic roles in human physiology. Circulating vitamin C concentrations are lower in people with diabetes mellitus, suggesting a higher dietary requirement for the vitamin. We interrogated the NHANES 2017-2018 and EPIC-Norfolk datasets to compare vitamin C requirements between those with and without diabetes mellitus using dose-concentration relationships fitted with sigmoidal (four-parameter logistic) curves. The NHANES cohort (n = 2828 non-supplementing adults) comprised 488 (17%) participants with diabetes (self-reported or HbA1c ≥ 6.5%). The participants with diabetes had a lower vitamin C status (median [IQR]) than those without (38 [17, 52] µmol/L vs. 44 [25, 61] µmol/L, p < 0.0001), despite comparable dietary intakes between the two groups (51 [26, 93] mg/d vs. 53 [24, 104] mg/d, p = 0.5). Dose-concentration relationships indicated that the group without diabetes reached adequate vitamin C concentrations (50 µmol/L) with an intake of 81 (72, 93) mg/d, whilst those with diabetes required an intake of 166 (126, NA) mg/d. In the EPIC-Norfolk cohort, comprising 20692 non-supplementing adults, 475 (2.3%) had self-reported diabetes at baseline. The EPIC cohort had a lower BMI than the NHANES cohort (26 [24, 28] kg/m2 vs. 29 [25, 34] kg/m2, p < 0.0001). Correspondingly, the EPIC participants without diabetes required a lower vitamin C intake of 64 (63, 65) mg/d while those with diabetes required 129 (104, NA) mg/d to reach adequate circulating vitamin C status. C-reactive protein concentrations were strongly correlated with body weight and BMI and provided a surrogate biomarker for vitamin C requirements. In conclusion, people with diabetes had 1.4 to 1.6 fold higher requirements for vitamin C than those without diabetes. This corresponds to additional daily vitamin C intake requirements of ~30-40 mg for people with diabetes, equating to a total daily intake of at least 125 mg/d.

Vitamin C Urinary Loss and Deficiency in Human Immunodeficiency Virus (HIV): Cross-sectional Study of Vitamin C Renal Leak in Women With HIV

BACKGROUND

Reduced plasma vitamin C (vitC) concentrations in human immunodeficiency virus (HIV) may result from abnormal urinary excretion: a renal leak. VitC renal leak indicates underlying nutritional dysregulation independent of diet. We hypothesized that increased renal leak prevalence in HIV would be associated with deficient vitC concentrations.

METHODS

We conducted an outpatient cross-sectional study of 96 women (40 HIV [PWH] and 56 without HIV [PWOH]) at the National Institutes of Health and Georgetown University. Renal leak was defined as abnormal urinary vitC excretion at fasting plasma concentrations <43.2µM, 2 SDs below vitC renal threshold in healthy women. To determine the primary outcome of renal leak prevalence, matched urine and plasma samples were collected the morning after overnight fast. Secondary outcomes assessed group differences in mean plasma vitC concentrations and prevalence of vitC deficiency. Exploratory outcomes assessed clinical parameters associated with renal leak. VitC was measured by high-performance liquid chromatography with coulometric electrochemical detection.

RESULTS

PWH had significantly higher renal leak prevalence (73%vs14%; OR (odds ratio):16; P<.001), lower mean plasma vitC concentrations (14µMvs50µM; P<.001), and higher prevalence of vitC deficiency (43%vs7%; OR:10; P<.001) compared with PWOH, unchanged by adjustments for confounding factors. Significant predictors of renal leak included antiretroviral therapy (ART), Black race, older age, and metabolic comorbidities but not viral load or CD4 count. When compared with other chronic disease cohorts, PWH had the highest prevalence of renal leak and vitC deficiency (P<.001).

CONCLUSIONS

High prevalence of vitC renal leak in HIV was associated with vitC deficiency, ART use, and race/ethnicity differences.

The effects of vitamin C supplementation on glycemic control in patients with type 2 diabetes: A systematic review and meta-analysis

BACKGROUND AND AIM

It has been suggested that taking vitamin C supplements may improve glycemic control in patients with type 2 diabetes mellitus (T2DM). However, there has not been a thorough evaluation of the actual impact or certainty of the findings. This systematic review and meta-analysis was conducted to determine the effect of vitamin C supplementation on glycemic profile in T2DM patients.

METHODS

A systematic search was performed across online databases including Scopus, Web of Science, and PubMed/Medline to identify relevant randomized controlled trials (RCTs) published until July 2022. A random-effects model was applied for the meta-analysis.

RESULTS

The present meta-analysis included a total of 22 RCTs with 1447 patients diagnosed with T2DM.A pooled analysis revealed a significant decrease in levels of serum hemoglobin A1c (HbA1c), fasting insulin, and fasting blood glucose (FBG) in vitamin C-treated T2DM patients compared with their untreated counterparts. The dose-response evaluation displayed a substantial linear association between the intervention duration and changes in serum HbA1c levels. However, the analysis did not demonstrate any significant effect of vitamin C on serum values of homeostasis model assessment of insulin resistance(HOMA-IR) in diabetic patients. Subgroup analyses indicated that high-dose vitamin C administration (≥1000 mg/d) considerably decreased serum HOMA-IR levels.

CONCLUSION

These findings suggest that long-term (≥12 weeks) and high-dose vitamin C supplementation (≥1000 mg/d) may ameliorate glycemic profile in T2DM patients. However, additional high-quality RCTs are necessary to validate these results.

Vitamin C Urinary Loss in Fabry Disease: Clinical and Genomic Characteristics of Vitamin C Renal Leak

BACKGROUND

Reduced plasma vitamin C concentrations in chronic diseases may result from abnormal urinary excretion of vitamin C: a renal leak. We hypothesized that vitamin C renal leak may be associated with disease-mediated renal dysregulation, resulting in aberrant vitamin C renal reabsorption and increased urinary loss.

OBJECTIVES

We investigated the prevalence, clinical characteristics, and genomic associations of vitamin C renal leak in Fabry disease, an X-linked lysosomal disease associated with renal tubular dysfunction and low plasma vitamin C concentrations.

METHODS

We conducted a non-randomized cross-sectional cohort study of men aged 24-42 y, with Fabry disease (n = 34) and controls without acute or chronic disease (n = 33). To match anticipated plasma vitamin C concentrations, controls were placed on a low-vitamin C diet 3 wk before inpatient admission. To determine the primary outcome of vitamin C renal leak prevalence, subjects were fasted overnight, and matched urine and fasting plasma vitamin C measurements were obtained the following morning. Vitamin C renal leak was defined as presence of urinary vitamin C at plasma concentrations below 38 μM. Exploratory outcomes assessed the association between renal leak and clinical parameters, and genomic associations with renal leak using single nucleotide polymorphisms (SNPs) in the vitamin C transporter SLC23A1.

RESULTS

Compared with controls, the Fabry cohort had 16-fold higher odds of renal leak (6% vs. 52%; OR: 16; 95% CI: 3.30, 162; P < 0.001). Renal leak was associated with higher protein creatinine ratio (P < 0.01) and lower hemoglobin (P = 0.002), but not estimated glomerular filtration rate (P = 0.54). Renal leak, but not plasma vitamin C, was associated with a nonsynonymous single nucleotide polymorphism in vitamin C transporter SLC23A1 (OR: 15; 95% CI: 1.6, 777; P = 0.01).

CONCLUSIONS

Increased prevalence of renal leak in adult men with Fabry disease may result from dysregulated vitamin C renal physiology and is associated with abnormal clinical outcomes and genomic variation.

The Role of Natural Antioxidant Products That Optimize Redox Status in the Prevention and Management of Type 2 Diabetes

The worldwide prevalence of type 2 diabetes (T2D) and prediabetes is rapidly increasing, particularly in children, adolescents, and young adults. Oxidative stress (OxS) has emerged as a likely initiating factor in T2D. Natural antioxidant products may act to slow or prevent T2D by multiple mechanisms, i.e., (1) reducing mitochondrial oxidative stress, (2) preventing the damaging effects of lipid peroxidation, and (3) acting as essential cofactors for antioxidant enzymes. Natural antioxidant products should also be evaluated in the context of the complex physiological processes that modulate T2D-OxS such as glycemic control, postprandial OxS, the polyol pathway, high-calorie, high-fat diets, exercise, and sleep. Minimizing processes that induce chronic damaging OxS and maximizing the intake of natural antioxidant products may provide a means of preventing or slowing T2D progression. This "optimal redox" (OptRedox) approach also provides a framework in which to discuss the potential benefits of natural antioxidant products such as vitamin E, vitamin C, beta-carotene, selenium, and manganese. Although there is a consensus that early effective intervention is critical for preventing or reversing T2D progression, most research has focused on adults. It is critical, therefore, that future research include pediatric populations.

Molecular modelling and biological evaluation of phyto-molecules as potential activators of gluconolactone oxidase (GULO)

Diabetes, the cause of colossal economic and disease burden, is a key area of research in drug discovery programs. Elevated blood glucose levels in diabetes lead to several adverse consequences due to the formation of advanced glycation end products and free radicals. Vitamin C, a potent antioxidant, protects the body's cells and tissues from oxidative damage and dysfunctions. Glucose is the precursor of Vitamin C synthesis in plants and some mammals. L-gulono lactone oxidase (GULO) is the rate-limiting enzyme in producing Vitamin C. However, it is not synthesized in bats, primates, humans, and guinea pigs because of the pseudogene. Several phytomolecules having antioxidant properties are hypothesized to be promising and selective activators of GULO. Therefore, the present study focused on screening agonists of GULO from phytomolecules as an effective augmentor for Vitamin C synthesis, thereby suppressing the sequela of diabetic events. The 3D structure of GULO was generated by the ab-initio method. Subsequently, molecular docking explored the possible binding patterns of GULO protein with different plant phenolic compounds, followed by supplementation of the potent phytomolecules to diabetic guinea pigs. It is noteworthy that Resveratrol and Hydroxytyrosol showed better binding affinity. The molecular simulation also confirmed that Resveratrol is an activator of the GULO enzyme. Interestingly, it was also established that Vitamin C levels were improved in diabetic guinea pigs supplemented with the phytomolecules and comparatively Resveratrol modulates the concentration of glucose and Vitamin C levels substantially, thereby alleviating hyperglycemia. However, further studies are warranted to study the mechanisms.Communicated by Ramaswamy H. Sarma.

People with diabetes and hypovitaminosis C fail to conserve urinary vitamin C

Background

Hypovitaminosis C has negative health consequences. People with diabetes and hypovitaminosis C may fail to conserve vitamin C in the urine, thereby displaying evidence of inappropriate renal leak of vitamin C. This study describes the relationship between plasma and urinary vitamin C in diabetes, with a focus on the clinical characteristics of participants with renal leak.

Methods

Retrospective analysis of paired, non-fasting plasma and urine vitamin C, and also clinical characteristics, from participants with either type 1 or type 2 diabetes, recruited from a secondary care diabetes clinic. Plasma vitamin C thresholds for renal leak have been defined previously as 38.1 µmol/L for men and 43.2 µmol/L for women.

Results

Statistically significant differences in clinical characteristics were seen between those with; i) renal leak (N = 77) and; ii) hypovitaminosis C but no renal leak (N = 13) and; iii) normal plasma vitamin C levels (n = 34). Compared to participants with adequate plasma vitamin C levels, participants with renal leak tended to have type 2 (rather than type 1) diabetes, a lower eGFR and a higher HbA1c.

Conclusion

In the diabetes population studied, renal leak of vitamin C was common. In some participants, it may have contributed to hypovitaminosis C.

Vitamin C supplementation for diabetes management: A comprehensive narrative review

Growing evidence suggests that vitamin C supplementation may be an effective adjunct therapy in the management of people with diabetes. This paper critically reviews the current evidence on effects of vitamin C supplementation and its potential mechanisms in diabetes management. Evidence from meta-analyses of randomized controlled trials (RCTs) show favourable effects of vitamin C on glycaemic control and blood pressure that may be clinically meaningful, and mixed effects on blood lipids and endothelial function. However, evidence is mostly of low evidence certainty. Emerging evidence is promising for effects of vitamin C supplementation on some diabetes complications, particularly diabetic foot ulcers. However, there is a notable lack of robust and well-designed studies exploring effects of vitamin C as a single compound supplement on diabetes prevention and patient-important outcomes (i.e. prevention and amelioration of diabetes complications). RCTs are also required to investigate potential preventative or ameliorative effects of vitamin C on gestational diabetes outcomes. Oral vitamin C doses of 500-1000 mg per day are potentially effective, safe, and affordable for many individuals with diabetes. However, personalisation of supplementation regimens that consider factors such as vitamin C status, disease status, current glycaemic control, vitamin C intake, redox status, and genotype is important to optimize vitamin C's therapeutic effects safely. Finally, given a high prevalence of vitamin C deficiency in patients with complications, it is recommended that plasma vitamin C concentration be measured and monitored in the clinic setting.

Microbial vitamin production mediates dietary effects on diabetic risk

Adequate levels of essential vitamins are important for the prevention of diabetes. While the main efforts to address this are currently focused on the intake of vitamin supplements, improving and maintaining intrinsic vitamin production capacity, which is determined by gut microbes, has received insufficient attention. In this study, we systematically investigated the relationship between gut microbial vitamin production and factors related to diabetes and cardiometabolic health in a deeply phenotyped cohort, Lifelines-DEEP (N = 1,135). We found that blood glucose-related factors, lipids, circulating inflammation, and fecal short-chain fatty acids are associated with gut microbial vitamin production. Use of laxatives and metformin are associated with increased levels of vitamin B1/B6 biosynthesis pathways. We further reveal a mediatory role for microbial vitamin B1/B2 production on the influence of fruit intake on diabetes risk. This study provides preliminary evidence for microbiome-targeted vitamin metabolism interventions to promote health.