Serum vitamin C concentrations and diabetes: findings from the Third National Health and Nutrition Examination Survey, 1988-1994

Predictive model for vitamin C levels in hyperinsulinemic individuals based on age, sex, waist circumference, low-density lipoprotein, and immune-associated serum proteins

Vitamin C (ascorbic acid) is an important water-soluble antioxidant associated with decreased oxidative stress in type 2 diabetes (T2D) patients. A previous targeted plasma proteomic study has indicated that ascorbic acid is associated with markers of the immune system in healthy subjects. However, the association between the levels of ascorbic acid and blood biomarkers in subjects at risk of developing T2D is still unknown. Serum ascorbic acid was measured by ultra-performance liquid chromatography and serum proteins were quantified by untargeted liquid-chromatography mass spectrometry in 25 hyperinsulinemia subjects that were randomly assigned a high dairy intake diet or an adequate dairy intake diet for 6 weeks, then crossed-over after a 6-week washout period. Spearman correlation followed by gene ontology analyses were performed to identify biological pathways associated with ascorbic acid. Finally, machine learning analysis was performed to obtain a specific serum protein signature that could predict ascorbic acid levels. After adjustments for waist circumference, LDL, HDL, fasting insulin, fasting blood glucose, age, gender, and dairy intake; serum ascorbic acid correlated positively with different aspects of the immune system. Machine learning analysis indicated that a signature composed of 21 features that included 17 proteins (mainly from the immune system), age, sex, waist circumference, and LDL could predict serum ascorbic acid levels in hyperinsulinemia subjects. In conclusion, the result reveals a correlation as well as modulation between serum ascorbic acid levels and proteins that play vital roles in regulating different aspects of the immune response in individuals at risk of T2D. The development of a predictive signature for ascorbic acid will further help the assessment of ascorbic acid status in clinical settings.

Low Levels of Vitamin C during Pregnancy; a Risk Marker of Progression of Diabetic Retinopathy in Type 1 Diabetic Women?

Pregnancy is a risk factor for the development or aggravation of diabetic retinopathy. Here, we suggest a relationship between plasma vitamin C (vitC) status during pregnancy and into postpartum in type 1 diabetes and the possible progression of diabetic retinopathy based on data of 29 women. VitC was measured in first, second, and third trimesters and three months postpartum. The women had visual acuity testing and fundus photography performed at least twice during pregnancy and onto four months after birth. An overall retinopathy grade was assigned on a scale from 0 (no retinopathy) to four according to the International Clinical Diabetic Retinopathy scale. At baseline in 1st trimester, 12 women had no retinopathy; seventeen women had retinopathy in grade 1–3. The retinopathy grade increased in nine women; remained unchanged in 17 women, and improved in three women. No women had or developed proliferative retinopathy (grade 4). The level of vitC in 1st trimester predicted the possible progression of retinopathy—the lower the vitC, the more probable the progression (p = 0.03; OR 1.6 (95% CI:1.06–3.2); n = 29 (multiple logistic regression))—while the combined levels of 1st and 2nd trimesters and the mean vitC level of the whole pregnancy did not. The diabetes duration, retinopathy grade per se in 1st trimester, 24-h blood pressure measurements, kidney function, urinary protein, HbA1c, or lipid profile were not independent predictors of progression of retinopathy during pregnancy. Retrospectively, the women who experienced progression of their retinopathy during and into postpartum had significantly lower vitC levels in 1st trimester (p = 0.02; n = 9/20), combined level of vitC in 1st and 2nd trimester (p = 0.032; n = 7/18), and mean vitC level of the whole pregnancy (p = 0.036; n = 7/9), respectively. In conclusion, our results suggest that low vitC status in pregnancy could be associated with progression of diabetic retinopathy.

Oxidative Regulation of Vascular Cav1.2 Channels Triggers Vascular Dysfunction in Hypertension-Related Disorders

Blood pressure is determined by cardiac output and peripheral vascular resistance. The L-type voltage-gated Ca²⁺ (Ca_v1.2) channel in small arteries and arterioles plays an essential role in regulating Ca²⁺ influx, vascular resistance, and blood pressure. Hypertension and preeclampsia are characterized by high blood pressure. In addition, diabetes has a high prevalence of hypertension. The etiology of these disorders remains elusive, involving the complex interplay of environmental and genetic factors. Common to these disorders are oxidative stress and vascular dysfunction. Reactive oxygen species (ROS) derived from NADPH oxidases (NOXs) and mitochondria are primary sources of vascular oxidative stress, whereas dysfunction of the Ca_v1.2 channel confers increased vascular resistance in hypertension. This review will discuss the importance of ROS derived from NOXs and mitochondria in regulating vascular Ca_v1.2 and potential roles of ROS-mediated Ca_v1.2 dysfunction in aberrant vascular function in hypertension, diabetes, and preeclampsia.

Decreasing Vitamin C Intake, Low Serum Vitamin C Level and Risk for US Adults with Diabetes

Vitamin C (VC) intakes, serum VC, fasting plasma glucose, and A1c levels of 25,206 adult men and 26,944 adult women with 6807 type 2 and 428 type 1 diabetes from the NHANES database between 1999 and 2018 were analyzed. Our hypothesis is that low VC intake and serum VC level may be a health risk for US adults with diabetes. Analyses revealed total VC intake below the estimated average requirement (EAR) increased from 38.1% to 46.5% between 1999–2018. VC intake and serum VC levels were inversely associated with markers of pre-diabetes and type 2 diabetes, namely, fasting plasma glucose and A1c levels. Risks of type 2 diabetes increased in adults with VC intake below the EAR and with no VC supplement (odds ratio 1.20, 95% CI 1.1–1.3 and 1.28, 95% CI 1.18–1.40, respectively). Median survivor years of diabetic adults with lower and deficient serum VC were shorter than that of diabetic adults with normal serum VC. Mortality risks of type 2 diabetes with low VC intake and/or deficient serum VC levels were elevated compared to those with adequate VC intake and normal serum VC (HR 1.25, 95% CI 1.05–1.49 and 1.84, 95% CI 1.10–3.08, respectively). Observation of declining VC intake and deleterious consequences of low serum VC in US adults with diabetes suggests encouragement of VC intake, including VC supplementation of 500–1000 mg/day, may be beneficial for pre-diabetic and diabetic US adults.

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

BACKGROUND

Diabetes is associated with low plasma vitamin C concentrations.

OBJECTIVES

We investigated the contribution of dysregulated vitamin C renal physiology, its prevalence, and associated clinical characteristics.

METHODS

An essential prerequisite was determination of normal vitamin C renal threshold, the plasma concentration at which vitamin C first appears in urine. Using data from 17 healthy participants who underwent vitamin C depletion-repletion studies with a vitamin C dose range of 15-1250 mg daily, renal threshold was estimated using physiology-based pharmacokinetics modeling. Applying renal threshold 95% CIs, we estimated the minimal elimination threshold, the plasma concentration below which no vitamin C was expected in urine of healthy people. Renal leak was defined as abnormal presence of vitamin C in urine with plasma concentrations below the minimal elimination threshold. Criteria were tested in a cross-sectional cohort study of individuals with diabetes (82) and nondiabetic controls (80) using matched plasma and urine samples.

RESULTS

Vitamin C renal thresholds in healthy men and women were [mean (SD)] 48.5 (5.2) µM and 58.3 (7.5) µM, respectively. Compared with nondiabetic controls, participants with diabetes had significantly higher prevalence of vitamin C renal leak (9% compared with 33%; OR: 5.07; 95% CI: 1.97, 14.83; P < 0.001) and 30% lower mean plasma vitamin C concentrations (53.1 µM compared with 40.9 µM, P < 0.001). Fasting plasma glucose, glycosylated hemoglobin A1c, BMI, micro/macrovascular complications, and protein/creatinine ratio were predictive of vitamin C renal leak.

CONCLUSIONS

Increased prevalence of vitamin C renal leak in diabetes is associated with reduced plasma vitamin C concentrations. Glycemic control, microvascular complications, obesity, and proteinuria are predictive of renal leak.

Oxidative stress in the pathophysiology of type 2 diabetes and related complications: Current therapeutics strategies and future perspectives

Type 2 diabetes (T2DM) is a persistent metabolic disorder rising rapidly worldwide. It is characterized by pancreatic insulin resistance and β-cell dysfunction. Hyperglycemia induced reactive oxygen species (ROS) production and oxidative stress are correlated with the pathogenesis and progression of this metabolic disease. To counteract the harmful effects of ROS, endogenous antioxidants of the body or exogenous antioxidants neutralise it and maintain bodily homeostasis. Under hyperglycemic conditions, the imbalance between the cellular antioxidant system and ROS production results in oxidative stress, which subsequently results in the development of diabetes. These ROS are produced in the endoplasmic reticulum, phagocytic cells and peroxisomes, with the mitochondrial electron transport chain (ETC) playing a pivotal role. The exacerbated ROS production can directly cause structural and functional modifications in proteins, lipids and nucleic acids. It also modulates several intracellular signaling pathways that lead to insulin resistance and impairment of β-cell function. In addition, the hyperglycemia-induced ROS production contributes to micro- and macro-vascular diabetic complications. Various in-vivo and in-vitro studies have demonstrated the anti-oxidative effects of natural products and their derived bioactive compounds. However, there is conflicting clinical evidence on the beneficial effects of these antioxidant therapies in diabetes prevention. This review article focused on the multifaceted role of oxidative stress caused by ROS overproduction in diabetes and related complications and possible antioxidative therapeutic strategies targeting ROS in this disease.

Adherence to a healthy dietary pattern is associated with greater anti-oxidant capacity and improved glycemic control in Iraqi patients with Type 2 Diabetes

BACKGROUND: Healthy dietary patterns are typically associated with improved metabolic and cardiovascular health in population-based cohorts. This study aims to investigate whether a healthy dietary score, derived from UK Diabetes and Diet Questionnaire (UKDDQ), is significantly associated with measures of metabolic health and nutritional status in patients with T2DM. METHODS: This cross-sectional study included 85 patients with T2DM (age: 51.7±9.4, BMI: 30.6±5.3) and 20 healthy volunteers (age: 48.4±8.6, BMI: 29.5±5) recruited from the Al-Hassan Diabetes and Endocrinology Specialized Center, Karbala, Iraq. Body weight, height and body mass index (BMI) and resting clinic blood pressure were measured. All participants completed the UKDDQ to assess the quality of the diet. Metabolic and nutritional biomarkers were measured in fasting blood samples. A composite nutritional heathy index score (CNHI-score) based on the sum of z-scores for plasma vitamin A, C and E concentrations was derived. RESULTS: In patients with T2DM the UKDDQ score was associated with lower fasting blood glucose (FBG) (r = –0.33; P <  0.01), hemoglobin A1C (r = –0.49; P <  0.001), total cholesterol (TC) (r = –0.26; P = 0.02) concentrations. In patients with T2DM, the CNHI-score significantly associated with UKDDQ (r = 0.43; P <  0.001). In addition, a higher CNHI-score was associated with FBG (r = –0.61; P <  0.001), HbA1C (r = –0.83; P <  0.001), TC (r = –0.30; P <  0.01) and triglyceride (r = –0.30; P <  0.01) concentrations. CONCLUSIONS: A healthy diet is associated with a higher concentration of anti-oxidant vitamins and better glycemic and lipid profile in healthy subjects and in patients with T2DM.

Effect of Vitamin C as an Adjunct in Nonsurgical Periodontal Therapy in Uncontrolled Type 2 Diabetes Mellitus Patients

Objective  The main purpose of this article is to evaluate periodontal parameters of chronic periodontitis patients with uncontrolled type 2 diabetes mellitus after initial periodontal therapy plus vitamin C.

Materials and Methods  A double-blind, placebo-controlled, clinical trial was conducted. Subjects received initial periodontal therapy plus 500 mg/day vitamin C for 2 months ( n = 15) or placebo ( n = 16). Fasting blood sugar (FBS), hemoglobin A1c (HbA1C), and plasma vitamin C level were assessed at baseline and 2 months post-treatment. Plaque Index, Sulcus Bleeding Index, Gingival Index, pocket depth, and clinical attachment level were measured at baseline, 1 month, and 2 months post-treatment.

Results  Almost all subjects had low level of plasma vitamin C at baseline. In the test group, plasma vitamin C was significantly increased to an adequate level at the end of 2 months. After periodontal treatment, FBS and HbA1c were not significantly different compared with baseline in the test group. In the control group, FBS was significantly decreased from baseline. However, no significant difference between groups was found either in FBS or HbA1c. All periodontal parameters were significantly improved from baseline in both groups. However, no significant difference was found between groups.

Conclusion  Supplementation of 500 mg/day vitamin C did not give an additional benefit in promoting periodontal status in periodontitis patients with uncontrolled type 2 diabetes mellitus.

Ascorbic acid therapy: A potential strategy against comorbid depression-like behavior in streptozotocin-nicotinamide-induced diabetic rats

This study examined the potency and efficacy of ascorbic acid (AA) in the management of depression-like behavior in diabetic rats. Diabetes mellitus was induced by single intraperitoneal injections of nicotinamide (120 mg/kg) and streptozotocin (65 mg/kg) administered 15 min apart. Diabetic (blood glucose ≥250 mg/dL) rats were subjected to intermittent foot-shocks to induce comorbid depression. Seven groups of diabetes comorbid depressed rats received vehicle (1 mL/kg) or AA (10, 25, 50, 100, 200, or 400 mg/kg) orally for eleven days. Three control groups namely- nondiabetic, diabetic, and depressed rats received the vehicles only. The potency (ED₅₀) and efficacy (E_max) of AA against immobility period, hypercorticosteronemia, adrenal hyperplasia, hyperglycemia, hypoinsulinemia, oxidative stress, and inflammatory response were estimated. AA administration caused a dose-dependent decrease (P < 0.05) in immobility period with maximum inhibition of 69% (efficacy) at 200 mg/kg and ED₅₀ of 14 mg/kg (potency). AA at 200 mg/kg produced the maximal reduction in hypercorticosteronemia (55.1%) and adrenal hyperplasia (52.6%) with ED₅₀ of 9.8 and 14.4 mg/kg, respectively. AA at 400 mg/kg produced the maximal reduction in hyperglycemia (35.5%), hypoinsulinemia (32.7%), and lipid peroxidation (82%) with ED₅₀ of 18.6, 13.7, and 20.7 mg/kg, respectively. Moreover, AA at 400 mg/kg produced the maximal increase in SOD content (83%), CAT activity (77.9%), and IL-10 level (63%) with ED₅₀ of 21.5, 21, and 21 mg/kg, respectively. In conclusion, the present results suggest that AA has therapeutic potential against diabetes comorbid depression but better regulation of hyperglycemia and hypoinsulinemia is required to achieve maximal benefits.

SunGold Kiwifruit Supplementation of Individuals with Prediabetes Alters Gut Microbiota and Improves Vitamin C Status, Anthropometric and Clinical Markers

Kiwifruit are a nutrient dense food and an excellent source of vitamin C. Supplementation of the diet with kiwifruit enhances plasma vitamin C status and epidemiological studies have shown an association between vitamin C status and reduced insulin resistance and improved blood glucose control. In vitro experiments suggest that eating kiwifruit might induce changes to microbiota composition and function; however, human studies to confirm these findings are lacking. The aim of this study was to investigate the effect of consuming two SunGold kiwifruit per day over 12 weeks on vitamin C status, clinical and anthropometric measures and faecal microbiota composition in people with prediabetes. This pilot intervention trial compared baseline measurements with those following the intervention. Participants completed a physical activity questionnaire and a three-day estimated food diary at baseline and on completion of the trial. Venous blood samples were collected at each study visit (baseline, 6, 12 weeks) for determination of glycaemic indices, plasma vitamin C concentrations, hormones, lipid profiles and high-sensitivity C-reactive protein. Participants provided a faecal sample at each study visit. DNA was extracted from the faecal samples and a region of the 16S ribosomal RNA gene was amplified and sequenced to determine faecal microbiota composition. When week 12 measures were compared to baseline, results showed a significant increase in plasma vitamin C (14 µmol/L, p < 0.001). There was a significant reduction in both diastolic (4 mmHg, p = 0.029) and systolic (6 mmHg, p = 0.003) blood pressure and a significant reduction in waist circumference (3.1 cm, p = 0.001) and waist-to-hip ratio (0.01, p = 0.032). Results also showed a decrease in HbA1c (1 mmol/mol, p = 0.005) and an increase in fasting glucose (0.1 mmol/L, p = 0.046), however, these changes were small and were not clinically significant. Analysis of faecal microbiota composition showed an increase in the relative abundance of as yet uncultivated and therefore uncharacterised members of the bacterial family Coriobacteriaceae. Novel bacteriological investigations of Coriobacteriaceae are required to explain their functional relationship to kiwifruit polysaccharides and polyphenols.

Identification of new candidate genes for retinopathy in type 2 diabetics. Valencia Study on Diabetic Retinopathy (VSDR). Report number 3

OBJECTIVE

To identify genes involved in the pathogenic mechanisms of non-proliferative diabetic retinopathy (NPDR), among which include oxidative stress, extracellular matrix changes, and/or apoptosis, in order to evaluate the risk of developing this retinal disease in a type2 diabetic (DM2) population.

MATERIAL AND METHODS

A case-control study was carried out on 81 participants from the Valencia Study on Diabetic Retinopathy (VSDR) of both genders, with ages 25-85years. They were classified into: (i)DM2 group (n=49), with DR (+DR; n=14) and without DR (-DR; n=35), and (ii)control group (GC; n=32). The protocols included a personal interview, standardised ophthalmological examination, and blood collection (to analyse the DNA for determining the gene expression (TP53, MMP9, and SLC23A2) in the study groups. Statistical analyses were performed using the SPSS v22.0 program.

RESULTS

The TP53 and MMP9 genes showed a higher expression in the DM2 group compared to the GC, although the difference was only significant for the MMP9 gene (TP53: 10.40±1.20 vs. 8.23±1.36, P=.084; MMP9: 1.45±0.16 vs. 0.95±0.16, P=.036), and the SLC23A2 gene showed a significant lower expression in the DM2 vs CG (5.58±0.64 vs. 11.66±1.90, P=.026). When sub-dividing the DM2 group according to the presence of retinopathy, the expression of the TP53, MMP9 and SLC23A2 genes showed significant differences between the DM2-RD, DM2+RD and GC groups (TP53: 9.95±1.47 vs. 11.52±2.05 vs. 8.23±1.36, P=.038; MMP9: 1.47±0.20 vs. 1.41±0.27 vs. 0.95±0.16, P=.021; SLC23A2: 5.61±0.77 vs. 5.51±1.21 vs. 11.66±1.90, P=.018).

CONCLUSIONS

Genes involved in extracellular matrix integrity (MMP9) and/or apoptosis (TP53), could be considered potential markers of susceptibility to the development/progression of NPDR. Interestingly, the SLC232A2 gene (ascorbic acid transporter) can be considered a protector of the risk of the development/progression of the retinopathy.

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

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.

Effects of vitamin C supplementation on glycaemic control: a systematic review and meta-analysis of randomised controlled trials

Randomised controlled trials (RCTs) have observed contrasting results on the effects of vitamin C on circulating biomarkers of glycaemic and insulin regulation. We conducted a systematic review and meta-analysis of RCTs testing the effect of vitamin C administration on glucose, HbA1c and insulin concentrations. Four databases (PubMed, Embase, Scopus and Cochrane Library) were used to retrieve RCTs published from inception until April 2016 and testing the effects of vitamin C in adult participants. The screening of 2008 articles yielded 22 eligible studies (937 participants). Overall, vitamin C did not modify glucose, HbA1c and insulin concentrations. However, subgroup analyses showed that vitamin C significantly reduced glucose concentrations (-0.44 mmol/l, 95% CI: -0.81, -0.07, P=0.01) in patients with type 2 diabetes and in interventions with a duration greater than 30 days (-0.53%, 95% CI: -0.79, -0.10, P=0.02). Vitamin C administration had greater effects on fasting (-13.63 pmol/l, 95% CI: -22.73, -4.54, P<0.01) compared to postprandial insulin concentration. Meta-regression analyses showed that age was a modifier of the effect of vitamin C on insulin concentration. Furthermore, the effect size was associated with baseline BMI and plasma glucose levels, and with the duration of the intervention. In conclusion, greater reduction in glucose concentrations observed in patients with diabetes, older individuals and with more prolonged supplementation. Personalised interventions with vitamin C may represent a feasible future strategy to enhance benefits and efficacy of interventions. Nevertheless, results need to be interpreted cautiously due to limitations in the primary studies analysed.

Dietary Vitamin C Intake Reduces the Risk of Type 2 Diabetes in Chinese Adults: HOMA-IR and T-AOC as Potential Mediators

Despite growing interest in the protective role that dietary antioxidant vitamins may have in the development of type 2 diabetes (T2D), little epidemiological evidence is available in non-Western populations especially about the possible mediators underlying in this role. The present study aimed to investigate the association of vitamin C and vitamin E intakes with T2D risk in Chinese adults and examine the potential mediators. 178 incident T2D cases among 3483 participants in the Harbin People Health Study (HPHS), and 522 newly diagnosed T2D among 7595 participants in the Harbin Cohort Study on Diet, Nutrition and Chronic Non-communicable Diseases (HDNNCDS) were studied. In the multivariable-adjusted logistics regression model, the relative risks (RRs) were 1.00, 0.75, and 0.76 (P_trend = 0.003) across tertiles of vitamin C intake in the HDNNCDS, and this association was validated in the HPHS with RRs of 1.00, 0.47, and 0.46 (P_trend = 0.002). The RRs were 1.00, 0.72, and 0.76 (P_trend = 0.039) when T2D diagnosed by haemoglobin A_1c in the HDNNCDS. The mediation analysis discovered that insulin resistance (indicated by homeostasis model assessment) and oxidative stress (indicated by plasma total antioxidative capacity) partly mediated this association. But no association was evident between vitamin E intake and T2D. In conclusion, our research adds further support to the role of vitamin C intake in reducing the development of T2D in the broader population studied. The results also suggested that this association was partly mediated by inhibiting or ameliorating oxidative stress and insulin resistance.

Vitamin C: the known and the unknown and Goldilocks

Vitamin C (Ascorbic Acid), the antiscorbutic vitamin, cannot be synthesized by humans and other primates, and has to be obtained from diet. Ascorbic acid is an electron donor and acts as a cofactor for fifteen mammalian enzymes. Two sodium-dependent transporters are specific for ascorbic acid, and its oxidation product dehydroascorbic acid is transported by glucose transporters. Ascorbic acid is differentially accumulated by most tissues and body fluids. Plasma and tissue vitamin C concentrations are dependent on amount consumed, bioavailability, renal excretion, and utilization. To be biologically meaningful or to be clinically relevant, in vitro and in vivo studies of vitamin C actions have to take into account physiologic concentrations of the vitamin. In this paper, we review vitamin C physiology; the many phenomena involving vitamin C where new knowledge has accrued or where understanding remains limited; raise questions about the vitamin that remain to be answered; and explore lines of investigations that are likely to be fruitful.

Fruit, vegetable and vitamin C intakes and plasma vitamin C: cross-sectional associations with insulin resistance and glycaemia in 9-10 year-old children

AIM

To examine whether low circulating vitamin C concentrations and low fruit and vegetable intakes were associated with insulin resistance and other Type 2 diabetes risk markers in childhood.

METHODS

We conducted a cross-sectional, school-based study in 2025 UK children aged 9-10 years, predominantly of white European, South-Asian and black African origin. A 24-h dietary recall was used to assess fruit, vegetable and vitamin C intakes. Height, weight and fat mass were measured and a fasting blood sample collected to measure plasma vitamin C concentrations and Type 2 diabetes risk markers.

RESULTS

In analyses adjusting for confounding variables (including socio-economic status), a one interquartile range higher plasma vitamin C concentration (30.9 μmol/l) was associated with a 9.6% (95% CI 6.5, 12.6%) lower homeostatic model assessment of insulin resistance value, 0.8% (95% CI 0.4, 1.2%) lower fasting glucose, 4.5% (95% CI 3.2, 5.9%) lower urate and 2.2% (95% CI 0.9, 3.4%) higher HDL cholesterol. HbA1c concentration was 0.6% (95% CI 0.2, 1.0%) higher. Dietary fruit, vegetable and total vitamin C intakes were not associated with any Type 2 diabetes risk markers. Lower plasma vitamin C concentrations in South-Asian and black African-Caribbean children could partly explain their higher insulin resistance.

CONCLUSIONS

Lower plasma vitamin C concentrations are associated with insulin resistance and could partly explain ethnic differences in insulin resistance. Experimental studies are needed to establish whether increasing plasma vitamin C can help prevent Type 2 diabetes at an early stage.

Leptin Level and Skipping Breakfast: The National Health and Nutrition Examination Survey III (NHANES III)

Skipping breakfast is a common dietary habit considered to be unhealthy. However, the mechanisms underlying skipping breakfast have not been fully explored. Leptin is a hormone that regulates food intake and energy storage and secretes in a diurnal rhythm with lowest levels in the morning. We examined the association between the serum leptin level and skipping breakfast in 5714 adults in the U.S. National Health and Nutrition Examination Survey III, 1988-1994. We defined breakfast as any food or beverage consumed between 5:00 a.m. and 10:00 a.m. using a single 24-h recall. Skipped breakfast was seen in 13.1%. In the logistic regression models with and without adjusting for adiposity and sex, leptin levels were not associated with skipping breakfast. After adjusting for age, race/ethnicity, and time of venipuncture, the association remained insignificant. After further adjusting for potential confounders: physical activity, alcohol intake, smoking and diabetes and after further adjusting for: dietary factors, insulin and glucose levels, there was a 9% and 11%-12%, respectively, statistically significantly higher likelihood of skipping breakfast if the leptin level was more than 50% greater. Further investigation into the biological reasons for skipping breakfast may be useful for promoting healthy lifestyles.

Java project on periodontal diseases: effect of vitamin C/calcium threonate/citrus flavonoids supplementation on periodontal pathogens, CRP and HbA1c

OBJECTIVE

To assess in a periodontally diseased rural population deprived from regular dental care and having poor dietary conditions, the effect of vitamin C/calcium threonate/citrus flavonoids (VitC/Ca/Fl) supplementation on subgingival microbiota and plasma levels of vitamin C, HbA1c and hsCRP.

MATERIAL & METHODS

The study population consisted of 98 subjects who previously participated in a prospective study on the natural history of periodontitis. Participants were instructed to consume one tablet/day containing 200 mg Ester C(®) calcium ascorbate, 25 mg calcium threonate and 100 mg citrus flavonoids for 90 days. Following parameters were evaluated: prevalence/amount of seven traditional periodontal pathogens, cytomegalovirus, Epstein-Barr virus (EBV); and plasma levels of vitamin C, HbA1c and hsCRP.

RESULTS

After VitC/Ca/Fl supplementation, 100% of subjects showed normal plasma vitamin C values compared to 55% before. At baseline, 48% of subjects harboured Aggregatibacter actinomycetemcomitans, >97% the other periodontal pathogens and 73% EBV. Supplementation with VitC/Ca/F reduced the subgingival load of all studied bacteria (p-values: 0.014-0.0001) and EBV (p < 0.0001) substantially in all initially positive subjects. Plasma levels of HbA1c and hsCRP dropped in all subjects (p < 0.0001).

CONCLUSION

This uncontrolled study suggested that supplemental VitC/Ca/Fl may be helpful in reducing subgingival numbers of periodontal pathogens and EBV, and promoting systemic health.

High-serum carotenoids associated with lower risk for developing type 2 diabetes among Japanese subjects: Mikkabi cohort study

OBJECTIVE

Recent epidemiological studies show the association of antioxidant carotenoids with type 2 diabetes, but thorough longitudinal cohort studies regarding this association have not been well conducted. The objective of this study was to investigate longitudinally whether serum carotenoids are associated with the risk for developing type 2 diabetes among Japanese subjects.

RESEARCH DESIGN AND METHODS

We conducted a follow-up study on 1073 males and females aged 30-79 years at the baseline from the Mikkabi prospective cohort study. Those who participated in the baseline and completed follow-up surveys were examined longitudinally. Over the 10-year period, 910 subjects (295 males and 615 females) took part in the follow-up survey at least one time. A cohort of 264 males and 600 females free of diabetes at baseline was studied.

RESULTS

Over a mean follow-up period of 7.8 years (SD=2.9), 22 males and 33 females developed new type 2 diabetes. After adjustments for confounders, the HRs for type 2 diabetes in the highest tertiles of serum α-carotene, β-cryptoxanthin, and total provitamin A carotenoids against the lowest tertiles were 0.35 (95% CI 0.15 to 0.82), 0.43 (CI 0.20 to 0.92) and 0.41 (CI 0.19 to 0.90), respectively. For β-carotene and zeaxanthin, borderline reduced risks were also observed, but these were not significant.

CONCLUSIONS

Our results further support the hypothesis that eating a diet rich in carotenoids, especially provitamin A carotenoids, might help prevent the development of type 2 diabetes in Japanese patients.

TRIAL REGISTRATION NUMBER

NIFT-2013001.

Prevention of diabetes-induced cardiovascular complications upon treatment with antioxidants

Oxidative stress is considered to play an important role in the pathogenesis of diabetes-induced cardiovascular disease (CVD), which is invariably associated with abnormal blood lipid profile, insulin resistance and metabolic syndrome. Stress, smoking, high saturated fat intake as well as low fruit and vegetable intakes have been shown to increase oxidative stress and hyperlipidemia, which increase the predisposition of diabetic subjects to atherosclerosis, stroke and coronary heart disease. The oxidation of low-density lipoprotein by oxidative stress is essential for the development of atherosclerosis, and the reduction in oxidative stress as well as blood glucose and cholesterol is considered critical for the prevention of diabetes-induced CVD. Although epidemiological studies have demonstrated that vitamin C and vitamin E decrease the incidence of coronary heart disease, different clinical trials have failed to support the beneficial effect of these antioxidants. Nonetheless, it has been suggested that natural forms of these vitamins may be more efficacious than synthetic vitamins, and this may explain the inconsistencies in results. Antioxidants, N-acetyl-L-cysteine and resveratrol, have also been shown to attenuate the diabetes-induced cardiovascular complications. It has been indicated that the antioxidant therapy may be effective in a prevention strategy rather than as a treatment for CVD. The evidence presented here supports the view that cardiovascular complications in diabetes may be induced by oxidative stress and appropriate antioxidant therapy may be promising for attenuating the progression of diabetes-induced CVD.

Response of thymus lymphocytes to streptozotocin-induced diabetes and exogenous vitamin C administration in rats

Diabetes causes oxidative stress, which in turn generates excessive free radicals resulting in cellular damage. Vitamin C is an antioxidant that protects tissues and organs from oxidative stress. The thymus is one of the most important lymphoid organs, which regulates T-lymphocyte proliferation and maturation. The aim of this study is to investigate the protective effects of vitamin C on the thymus of streptozotocin (STZ)-induced diabetic rats. The mitotic activity and cell integrity of thymic lymphocytes were explored. Wistar Albino rats were divided into three groups: control (Group 1), STZ-diabetes (Group 2) and vitamin C-treated STZ-diabetics (Group 3). Rats received a single intraperitoneal injection of 45 mg/kg STZ to induce diabetes. Vitamin C (20 mg/kg) was administered intragastrically. Semithin and ultrathin sections were examined under a light or an electron microscope, respectively. Considerable numbers of mitotic lymphocytes were observed in the thymus of control rats. In the diabetic rats, however, numbers of mitotic lymphocytes decreased to ∼57% of controls, and cell division abnormalities were observed. Additionally, diabetic rats showed degeneration in the structure of the thymus including trabecular thickening, accumulation of lipid vacuoles, heterochromatic nuclei and loss of mitochondrial cristae. Degradation of medullar and cortical integrity was also detected. In the vitamin C-treated STZ-diabetic group, the structure of the thymus and mitotic activity of the lymphocytes were similar to the control group. These results suggest that vitamin C protects the thymus against injury caused by diabetes and restores thymocyte mitotic activity.

Molecular mechanisms of diabetic vascular complications

Diabetic complications are the major causes of morbidity and mortality in patients with diabetes. Microvascular complications include retinopathy, nephropathy and neuropathy, which are leading causes of blindness, end‐stage renal disease and various painful neuropathies; whereas macrovascular complications involve atherosclerosis related diseases, such as coronary artery disease, peripheral vascular disease and stroke. Diabetic complications are the result of interactions among systemic metabolic changes, such as hyperglycemia, local tissue responses to toxic metabolites from glucose metabolism, and genetic and epigenetic modulators. Chronic hyperglycemia is recognized as a major initiator of diabetic complications. Multiple molecular mechanisms have been proposed to mediate hyperglycemia’s adverse effects on vascular tissues. These include increased polyol pathway, activation of the diacylglycerol/protein kinase C pathway, increased oxidative stress, overproduction and action of advanced glycation end products, and increased hexosamine pathway. In addition, the alterations of signal transduction pathways induced by hyperglycemia or toxic metabolites can also lead to cellular dysfunctions and damage vascular tissues by altering gene expression and protein function. Less studied than the toxic mechanisms, hyperglycemia might also inhibit the endogenous vascular protective factors such as insulin, vascular endothelial growth factor, platelet‐derived growth factor and activated protein C, which play important roles in maintaining vascular homeostasis. Thus, effective therapies for diabetic complications need to inhibit mechanisms induced by hyperglycemia’s toxic effects and also enhance the endogenous protective factors. The present review summarizes these multiple biochemical pathways activated by hyperglycemia and the potential therapeutic interventions that might prevent diabetic complications. (J Diabetes Invest, doi: 10.1111/j.2040‐1124.2010.00018.x, 2010)

Micronutrient status in type 2 diabetes: a review

Type 2 diabetes is characterized by significant losses of important micronutrients due to metabolic basis of the disease and its complications. Evidence of changes in trace mineral and vitamin metabolism as a consequence of type 2 diabetes is reviewed in this chapter. This review is not a meta-analysis but an overview of the micronutrient status, metabolic needs, and potential micronutrient requirements in type 2 diabetics. This chapter will not concentrate on vitamin D and type 2 diabetes as this is a topic that has been extensively reviewed before. The less well-known micronutrients notably zinc, magnesium, chromium, copper, manganese, iron, selenium, vanadium, B-group vitamins, and certain antioxidants are assessed. While some evidence is available to demonstrate the positive influence of micronutrient supplementation on glycemic control, much remains to be investigated. Additional research is necessary to characterize better biomarkers of micronutrient status and requirements in type 2 diabetics. The optimal level of micronutrient supplementation to achieve glucose homeostasis in type 2 diabetics remains a challenge.

Predictors of change in objectively measured and self-reported health behaviours among individuals with recently diagnosed type 2 diabetes: longitudinal results from the ADDITION-Plus trial cohort

BACKGROUND

There is limited evidence about predictors of health behaviour change in people with type 2 diabetes. The aim of this study was to assess change in health behaviours over one year and to identify predictors of behaviour change among adults with screen-detected and recently clinically diagnosed diabetes.

METHODS

ADDITION-Plus was a randomised controlled trial of a behaviour change intervention among 478 patients (40-69 years). Physical activity and diet were measured objectively (physical activity at 1 year) and by self-report at baseline and one year. Associations between baseline predictors and behaviour change were quantified using multivariable linear regression.

RESULTS

Participants increased their plasma vitamin C and fruit intake, reduced energy and fat intake from baseline to follow-up. Younger age, male sex, a smaller waist circumference, and a lower systolic blood pressure at baseline were associated with higher levels of objectively measured physical activity at one year. Greater increases in plasma vitamin C were observed in women (beta-coefficient [95% CI]: beta = -5.52 [-9.81, -1.22]) and in those with screen-detected diabetes (beta = 6.09 [1.74, 10.43]). Younger age predicted a greater reduction in fat (beta = -0.43 [-0.72, -0.13]) and energy intake (beta = -6.62 [-13.2, -0.05]). Patients with screen-detected diabetes (beta = 74.2 [27.92, 120.41]) reported a greater increase in fruit intake. There were no significant predictors of change in self-reported physical activity. Beliefs about behaviour change and diabetes did not predict behaviour change.

CONCLUSIONS

Older patients, men and those with a longer duration of diabetes may need more intensive support for dietary change. We recommend that future studies use objective measurement of health behaviours and that researchers add predictors beyond the individual level. Our results support a focus on establishing healthy lifestyle changes early in the diabetes disease trajectory.

The malnutrition of obesity: micronutrient deficiencies that promote diabetes

Obesity and diabetes are increasing in prevalence worldwide. Despite excessive dietary consumption, obese individuals have high rates of micronutrient deficiencies. Deficiencies of specific vitamins and minerals that play important roles in glucose metabolism and insulin signaling pathways may contribute to the development of diabetes in the obese population. This paper reviews the current evidence supporting this hypothesis.

Effect of vitamin e and selenium supplement on paraoxonase-1 activity, oxidized low density lipoprotein and antioxidant defense in diabetic rats

INTRODUCTION

The aim of the present study was to assess the effects of vitamin E and selenium supplementation on serum paraoxonase (PON1) activity, lipid peroxidation and antioxidant defense in streptozotocin-induced diabetic rats.

METHODS

Thirty two female Sprague Dawley rats were divided into 3 groups: the control group (n=8) received a standard diet; streptozotocin (STZ)-induced diabetic rats (n=12), received corn oil and physiological solution; and vitamin E and selenium supplemented diabetic rats (n=12) were treated with oral administration of vitamin E (300 mg/kg) and sodium selenite (0.5 mg/kg) once a day for 4 weeks.

RESULTS

Significantly lower total antioxidant status (TAS), PON1and erythrocyte SOD activities and a higher fasting plasma glucose level were observed in the diabetic rats compared to the control. A significant increase in SOD and GPX activities in vitamin E and selenium supplemented diabetic group was observed after 5 weeks of the experiment. Compared to the normal rats, malondialdehyde (MDA) and oxidized LDL (Ox-LDL) levels were higher in the diabetic animals; however, these values reduced significantly following vitamin E and selenium supplementation.

CONCLUSION

Vitamin E and selenium supplementation in diabetic rats has hypolipidemic, hypoglycemic and antioxidative effects and may slow down the progression of diabetic complications through its protective effect on PON1 activity and lipoproteins oxidation.

Effects of short-term streptozotocin-induced diabetes and vitamin C on platelet non-enzymatic glycation

Diabetes mellitus is one of the most prevalent metabolic syndromes worldwide. Glycation, a chemical modification of proteins with reducing sugars, indicates a possible explanation for the association between hyperglycemia and the wide variety of tissue pathologies. Non-enzymatic glycation (NEG) of platelet proteins is one of the key mechanisms in the pathogenesis of diabetic complications and may be significant in diabetic atherothrombosis. The aim of this study was to investigate the effects of streptozotocin (STZ)-induced short-term experimental diabetes on the glycation of platelets and to find out if vitamin C affected this glycation. A total of 40 male Wistar albino rats, 200-250 g, were randomly divided into 4 groups (2 diabetic and 2 control groups). The diabetic groups were made diabetic by intraperitoneal injection of STZ (65 mg/kg, citrate buffer pH 4.5). By daily intraperitoneal injection, 80 mg/kg vitamin C (Roche, Turkey) was administered until the end of the experiment. Blood glucose levels of the diabetic groups were significantly higher than those at day 0 and also higher than those of the non-diabetic control groups. The changes in total protein, NEG and vitamin C levels were not statistically significant. Although the differences among the groups were not statistically significant, vitamin C administration increased NEG levels in the diabetic group. The results of this study demonstrate that 8 days of STZ-induced short-term diabetes did not cause a significant increase in NEG of platelets. However, the effect of vitamin C on platelet NEG needs to be further investigated.

Multivitamins, individual vitamin and mineral supplements, and risk of diabetes among older U.S. adults

OBJECTIVE

Understanding the relationship between multivitamin use and diabetes risk is important given the wide use of multivitamin supplements among U.S. adults.

RESEARCH DESIGN AND METHODS

We prospectively examined supplemental use of multivitamins and individual vitamins and minerals assessed in 1995-1996 in relation to self-reported diabetes diagnosed after 2000 among 232,007 participants in the National Institutes of Health-American Association of Retired Persons Diet and Health Study. Multivitamin use was assessed by a food-frequency questionnaire at baseline. Odds ratios (ORs) and 95% CIs were calculated by logistic regression models, adjusted for potential confounders. In total, 14,130 cases of diabetes diagnosed after 2000 were included in the analysis.

RESULTS

Frequent use of any multivitamins was not associated with risk of diabetes after adjustment for potential confounders and uses of individual supplements. Compared with nonusers of any multivitamins, the multivariate ORs among users were 1.07 (95% CI 0.94-1.21) for taking vitamins less than once per week, 0.97 (0.88-1.06) for one to three times per week, 0.92 (0.84-1.00) for four to six times per week, and 1.02 (0.98-1.06) for seven or more times per week (P for trend = 0.64). Significantly lower risk of diabetes was associated with the use of vitamin C or calcium supplements. The multivariate ORs comparing daily users with nonusers were 0.91 (0.86-0.97) for vitamin C supplements and 0.85 (0.80-0.90) for calcium supplements. Use of vitamin E or other individual vitamin and mineral supplements were not associated with diabetes risk.

CONCLUSIONS

In this large cohort of U.S. older adults, multivitamin use was not associated with diabetes risk. The findings of lower diabetes risk among frequent users of vitamin C or calcium supplements warrant further evaluations.

Macrovascular complications of diabetes in atherosclerosisprone mice

The well-established relationship between diabetes and cardiovascular complications, combined with the rapidly increasing prevalence of diabetes, has created a pressing need for better understanding of the mechanisms of diabetic atherosclerosis. Multiple metabolic and diabetes-specific factors have been associated with accelerated atherosclerosis, including dyslipidemia, oxidative stress, inflammation, vascular cell dysfunction and coagulopathy. This discussion highlights selected studies in which researchers have employed mouse models of diabetic atherosclerosis in an attempt to examine these mechanisms and test potential therapeutic and preventative measures.

Effects of vitamins C and E and beta-carotene on the risk of type 2 diabetes in women at high risk of cardiovascular disease: a randomized controlled trial

BACKGROUND

Vitamin C, vitamin E, and beta-carotene are major antioxidants and as such may protect against the development of type 2 diabetes via reduction of oxidative stress.

OBJECTIVE

The purpose of this study was to investigate the long-term effects of supplementation with vitamin C, vitamin E, and beta-carotene for primary prevention of type 2 diabetes.

DESIGN

In the Women's Antioxidant Cardiovascular Study, a randomized trial that occurred between 1995 and 2005, 8171 female health professionals aged > or =40 y with either a history of cardiovascular disease (CVD) or > or =3 CVD risk factors were randomly assigned to receive vitamin C (ascorbic acid, 500 mg every day), vitamin E (RRR-alpha-tocopherol acetate, 600 IU every other day), beta-carotene (50 mg every other day), or their respective placebos.

RESULTS

During a median follow-up of 9.2 y, a total of 895 incident cases occurred among 6574 women who were free of diabetes at baseline. There was a trend toward a modest reduction in diabetes risk in women assigned to receive vitamin C compared with those assigned to receive placebo [relative risk (RR): 0.89; 95% CI: 0.78, 1.02; P = 0.09], whereas a trend for a slight elevation in diabetes risk was observed for vitamin E treatment (RR: 1.13; 95% CI: 0.99, 1.29; P = 0.07). However, neither of these effects reached statistical significance. No significant effect was observed for beta-carotene treatment (RR: 0.97; 95% CI: 0.85, 1.11; P = 0.68).

CONCLUSION

Our randomized trial data showed no significant overall effects of vitamin C, vitamin E, and beta-carotene on risk of developing type 2 diabetes in women at high risk of CVD. This trial was registered at clinicaltrials.gov as NCT00000541.

Positive and negative regulation of insulin signaling by reactive oxygen and nitrogen species

Regulated production of reactive oxygen species (ROS)/reactive nitrogen species (RNS) adequately balanced by antioxidant systems is a prerequisite for the participation of these active substances in physiological processes, including insulin action. Yet, increasing evidence implicates ROS and RNS as negative regulators of insulin signaling, rendering them putative mediators in the development of insulin resistance, a common endocrine abnormality that accompanies obesity and is a risk factor of type 2 diabetes. This review deals with this dual, seemingly contradictory, function of ROS and RNS in regulating insulin action: the major processes for ROS and RNS generation and detoxification are presented, and a critical review of the evidence that they participate in the positive and negative regulation of insulin action is provided. The cellular and molecular mechanisms by which ROS and RNS are thought to participate in normal insulin action and in the induction of insulin resistance are then described. Finally, we explore the potential usefulness and the challenges in modulating the oxidant-antioxidant balance as a potentially promising, but currently disappointing, means of improving insulin action in insulin resistance-associated conditions, leading causes of human morbidity and mortality of our era.

Diabetic neuropathy: mechanisms to management

Neuropathy is the most common and debilitating complication of diabetes and results in pain, decreased motility, and amputation. Diabetic neuropathy encompasses a variety of forms whose impact ranges from discomfort to death. Hyperglycemia induces oxidative stress in diabetic neurons and results in activation of multiple biochemical pathways. These activated pathways are a major source of damage and are potential therapeutic targets in diabetic neuropathy. Though therapies are available to alleviate the symptoms of diabetic neuropathy, few options are available to eliminate the root causes. The immense physical, psychological, and economic cost of diabetic neuropathy underscore the need for causally targeted therapies. This review covers the pathology, epidemiology, biochemical pathways, and prevention of diabetic neuropathy, as well as discusses current symptomatic and causal therapies and novel approaches to identify therapeutic targets.

Intake of fruit, vegetables, and antioxidants and risk of type 2 diabetes: systematic review and meta-analysis

BACKGROUND

The public health recommendation is to consume five or more servings of fruit and vegetables daily, but the association between the intake of fruit and vegetables and the risk of type 2 diabetes is unclear.

METHODS

To examine the association between the intake of fruit, vegetables, and antioxidants and the risk of type 2 diabetes, prospective cohort studies were sought, with measures of intakes at baseline and incident diabetes at follow-up.

RESULTS

Five cohort studies of fruit and vegetables intake and the risk of diabetes were included, incorporating 167,128 participants and 4858 incident cases of type 2 diabetes, with a mean follow-up of 13 years. The relative risk of type 2 diabetes for consuming five or more servings of fruit and vegetables daily was 0.96 (95% CI, 0.79-1.17, P = 0.96), 1.01 (0.88-1.15, P = 0.88) for three or more servings of fruit, and 0.97 (0.86-1.10, P = 0.59) for three or more servings of vegetables. Nine cohort studies of antioxidant intake and the risk of diabetes were also identified, incorporating 139,793 participants and 8813 incident cases of type 2 diabetes, with a mean follow-up of 13 years. The pooled relative risk was 0.87 (0.79-0.98, P = 0.02) for the highest compared with the lowest antioxidant intake.

CONCLUSIONS

The consumption of three or more daily servings of fruit or vegetables was not associated with a substantial reduction in the risk of type 2 diabetes. The intake of antioxidants was associated with a 13% reduction in risk, mainly attributed to vitamin E. These results are not supported by randomized, controlled trials of vitamin supplements, therefore the findings might not be causal, and the discrepancy remains unclear.

An overview of interactions between micronutrients and of micronutrients with drugs, genes and immune mechanisms

The objective of the present review is to examine critically the consequences of interactions that micronutrients undergo with nutrients and non-nutrients (mainly prescribed medicines) in diets and lifestyle factors (smoking, tea and alcohol consumption). In addition, the review describes recent work on interactions between nutrients and genes, the influence of gene polymorphisms on micronutrients, the impact of immune responses on micronutrients and specific interactions of antioxidant micronutrients in disease processes to minimise potential pro-oxidant damage.

Oxidative stress, chronic disease, and muscle wasting

Underlying the pathogenesis of chronic disease is the state of oxidative stress. Oxidative stress is an imbalance in oxidant and antioxidant levels. If an overproduction of oxidants overwhelms the antioxidant defenses, oxidative damage of cells, tissues, and organs ensues. In some cases, oxidative stress is assigned a causal role in disease pathogenesis, whereas in others the link is less certain. Along with underlying oxidative stress, chronic disease is often accompanied by muscle wasting. It has been hypothesized that catabolic programs leading to muscle wasting are mediated by oxidative stress. In cases where disease is localized to the muscle, this concept is easy to appreciate. Transmission of oxidative stress from diseased remote organs to skeletal muscle is thought to be mediated by humoral factors such as inflammatory cytokines. This review examines the relationship between oxidative stress, chronic disease, and muscle wasting, and the mechanisms by which oxidative stress acts as a catabolic signal.

The overlap of overweight and anaemia among women in three countries undergoing the nutrition transition

OBJECTIVE

To compare the odds of anaemia in overweight and obese (OVWT) (body mass index (BMI) > or =25) versus non-overweight (non-OVWT) (BMI<25) women in three countries at different stages of the nutrition transition.

DESIGN

Analysis of cross-sectional data.

SETTING

Nationally representative data from Mexico (1998 National Nutrition Survey), Peru and Egypt (2000 Demographic and Health Surveys) were analyzed.

SUBJECTS

Data from non-pregnant women ages 18-49 years were used.

ANALYSIS

Logistic regression was used to test whether the odds of anaemia differed by BMI category, controlling for sociodemographic factors.

RESULTS

More than half of the women were OVWT in all three countries and the prevalence of OVWT reached 77% in Egypt. Anaemia prevalence was similar across countries (28, 31 and 23% in Egypt, Peru and Mexico respectively). In Egypt, OVWT women had significantly lower odds of anaemia than non-OVWT women (OR=0.78, 95% CI: 0.68, 0.90). Similar results were found in Peru, but the difference was smaller in magnitude (OR=0.83, 95% CI: 0.71, 0.96). In Mexico, there were no differences in the odds of anaemia by BMI group.

CONCLUSIONS

These findings show that the iron needs of OVWT women in developing countries are not necessarily being met. The intakes of other micronutrients might also be insufficient. Diet quality remains an important issue even among women with sufficient energy intakes.

Safe levels of cadmium intake to prevent renal toxicity in human subjects

The present review attempts to provide an update of the scientific knowledge on the renal toxicity which occurs in human subjects as a result of chronic ingestion of low-level dietary Cd. It highlights important features of Cd toxicology and sources of uncertainty in the assessment of health risk due to dietary Cd. It also discusses potential mechanisms for increased susceptibility to Cd toxicity in individuals with diabetes. Exposure assessment on the basis of Cd levels in foodstuffs reveals that vegetables and cereals are the main sources of dietary Cd, although Cd is also found in meat, albeit to a lesser extent. Cd accumulates particularly in the kidney and liver, and hence offal contains relatively high amounts. Fish contains only small quantities of Cd, while crustaceans and molluscs may accumulate larger amounts from the aquatic environment. Data on Cd accumulation in human kidney and liver obtained from autopsy studies are presented, along with results of epidemiological studies showing the relationship between renal tubular dysfunction and kidney Cd burden. These findings suggest that a kidney Cd level of 50 μg/g wet weight is a maximum tolerable level in order to avoid abnormal kidney function. This renal Cd burden corresponds to a urinary Cd excretion of 2 μg/d. Accordingly, safe daily levels of Cd intake should be kept below 30 μg per person. Individual variations in Cd absorption and sensitivity to toxicity predicts that a dietary Cd intake of 30 μg/d may result in a slight renal dysfunction in about 1 % of the adult population. The previous guideline for a maximum recommended Cd intake of 1 μg/kg body weight per d is thus shown to be too high to ensure that renal dysfunction does not occur as a result of dietary Cd intake.

Cardiovascular disease prevention in patients with type 2 diabetes: The role of oral anti-diabetic agents

Multiple risk factor intervention is essential in order to prevent cardiovascular (CV) disease in patients with diabetes. Therefore, to reduce atherothrombotic events, an ideal oral anti-diabetic agent should be able to modulate most, and preferably all, cardiovascular risk factors associated with diabetes. Of the currently available agents, the insulin sensitisers (metformin, thiazolidinediones) seem to have most promise in cardiovascular protection. Metformin has a positive effect on several CV risk factors; outcome studies have shown that this agent reduces cardiac events in overweight subjects with diabetes. In a similar manner, thiazolidinediones (rosiglitazone, pioglitazone) have a wide spectrum of activity, favourably modulating most risk factors, with evidence to suggest a reduction in CV events with this class of drugs. Agents in the sulphonylurea group have beneficial, though inconsistent, effects on some risk factors but outcome studies have failed to show a cardioprotective role for these agents. New classes of drugs to manage type 2 diabetes are currently at various stages of development and their role in prevention of cardiovascular disease awaits evaluation. At present, first-line management of insulin-resistant type 2 diabetes should utilise metformin, with the addition of thiazolidinediones and sulphonylureas to achieve optimal glycaemic control.

Antioxidant supplementation does not affect fasting plasma glucose in the Supplementation with Antioxidant Vitamins and Minerals (SU.VI.MAX) study in France: association with dietary intake and plasma concentrations

BACKGROUND

Observational data suggest a protective effect of several antioxidants on fasting plasma glucose (FPG) and type 2 diabetes. However, randomized trials have yielded inconsistent results.

OBJECTIVES

The first objective was to assess the effect of 7.5 y of antioxidant supplementation on FPG at 7.5 y. The second objective was to examine the epidemiologic association of baseline dietary intakes or plasma antioxidants and FPG (at baseline and at 7.5 y).

DESIGN

Subjects (n = 3146) from the Supplementation en Vitamines et Minéraux Antioxydants (SU.VI.MAX) primary prevention trial in France were randomly assigned to receive a daily capsule containing 120 mg vitamin C, 30 mg vitamin E, 6 mg beta-carotene, 100 mug Se, and 20 mg Zn or a placebo.

RESULTS

After 7.5 y, no significant difference was observed between age-adjusted mean FPG in men (P = 0.78) and women (P = 0.89) in either group. Baseline beta-carotene dietary intakes and plasma concentrations were inversely associated with FPG in multivariate mixed models (P = 0.0045 and P < 0.0001, respectively). Baseline plasma vitamin C and selenium were negatively (P = 0.0455) and positively (P < 0.0001) associated, respectively, with FPG.

CONCLUSIONS

Supplementation with antioxidants at nutritional doses for 7.5 y had no effect on FPG in men or women who followed a balanced diet. An inverse association of baseline beta-carotene dietary intake and plasma concentrations with FPG was found, probably because beta-carotene is an indirect marker of fruit and vegetable intakes.

Short stature and the risk of adiposity, insulin resistance, and type 2 diabetes in middle age: the Third National Health and Nutrition Examination Survey (NHANES III), 1988-1994

OBJECTIVE

To investigate the association between stature-related measurements (height, leg length, and leg length-to-height ratio) and adiposity, insulin resistance, and glucose intolerance.

RESEARCH DESIGN AND METHODS

We conducted a cross-sectional analysis of a nationally representative sample of 7,424 adults aged 40-74 years, from the Third National Health and Nutrition Examination Survey (1988-1994). The main outcome measures were percent body fat, homeostasis model assessment of insulin resistance (HOMA-IR), and glucose intolerance based on the World Health Organization's 1985 criteria for an oral glucose tolerance test.

RESULTS

Shorter height and leg length, and lower leg length-to-height ratio, were associated with higher percent body fat, especially in women. Lower leg length-to-height ratio was associated with greater insulin resistance estimated by HOMA-IR. In multinomial regression models adjusting for potential confounders, including percent body fat, the relative prevalence of type 2 diabetes per 1-SD lower values in height, leg length, and leg length-to-height ratio were 1.10 (95% CI 0.94-0.29), 1.17 (0.98-1.39), and 1.19 (1.02-1.39), respectively.

CONCLUSIONS

Our study supports the hypothesis that adult markers of prepubertal growth, especially leg length-to-height ratio, are associated with adiposity, insulin resistance, and type 2 diabetes in the general U.S. population.

The role of PPARs in the microvascular dysfunction in diabetes

There is a major defect in skin blood flow (SkBF) in people with type 2 diabetes (T2DM). This defect is associated with relatively normal nitric oxide (NO) production in the skin. The abnormal blood flow cosegregates with hypertension, dyslipidemia, abnormal fatty acid composition, a proinflammatory state, and insulin resistance. Since these covariates are an integral part of the insulin resistance syndrome, we examined the effects of the thiazoledindiones (TZDs) as insulin sensitizers for their ability to correct the abnormal blood flow. The PPARgamma rosiglitazone improved NO production to normal levels, but had a small effect on SKBF. In contrast, pioglitazone had a small effect on skin neurovascular function but a dramatic effect on reducing nitrosative stress. These effects do not appear to be due to the insulin sensitizing properties of these compounds but are associated with a reduction in indices of inflammation, hemodilution, and are likely to be due to one of the many "vascular" effects of TZDs. The role of inflammation in the disordered neurovascular function in diabetes cannot be underplayed and the possible contribution of PPARalpha agonists to alter the inflammatory state needs to be explored further. Since blood flow regulation is mediated by mechanisms other than NO, such as prostaglandins and endothelial derived hyperpolarizing factor, which, in turn, are compromised by the inflammatory state, we anticipate that activation of both the PPARgamma as well as PPARalpha should ameliorate the disordered blood flow in type 2 diabetes. While it now appears that the PPARs may have a major role to play in protection from macrovascular disease, their contribution to amelioration of the microvascular defects in type 2 diabetes has fallen short of spectacular success. In this respect, the combinations of PPARalpha, PPARbeta and PPARgamma may better serve the unique requirements for improving the microvascular defect in diabetes.

The homeostasis model assessment-insulin resistance index is inversely associated with serum carotenoids in non-diabetic subjects

BACKGROUND

Carotenoids may reduce the risk for diabetes mellitus, but little is known about the association of insulin resistance with serum carotenoids in non-diabetic subjects. This study aimed to investigate whether the homeostasis model assessment-insulin resistance (HOMA-IR) index would be lower in the presence of high serum carotenoid concentrations in non-diabetic subjects.

METHODS

A total of 812 subjects (256 males and 556 females) who had received health examinations in 2003 participated in the study. The associations of the serum-carotenoid concentrations and HOMA-IR were evaluated cross-sectionally. The multivariate-adjusted geometric means of HOMA-IR by the tertiles of the serum carotenoid concentration were calculated after adjusting for age, body mass index, systolic blood pressure, total cholesterol, triacylglycerols, current tobacco use, regular alcohol intake, exercise habits and total energy intake. Associations among high HOMA-IR (3.0+ mU×mmol/L²) across tertiles of serum carotenoid concentration were assessed by tests for logistic regression analysis.

RESULTS

In male subjects, the multivariate adjusted geometric mean of HOMA-IR was inversely associated with the serum β-cryptoxanthin concentrations. In female subjects, an inverse association of the serum carotenoid concentration and HOMA-IR was observed in lycopene, β-cryptoxanthin, and zeaxanthin. The confounding factor-adjusted odds ratios (OR) for high HOMA-IR on the highest tertiles of serum α-carotene, β-carotene, β-cryptoxanthin, and zeaxanthin were 0.18 [95% confidence interval (CI): 0.06-0.52], 0.22 (95% CI: 0.07-0.67), 0.34 (95% CI: 0.12-0.96), and 0.30 (95% CI: 0.11-0.79), respectively, in male subjects. On the other hand, in female subjects, the adjusted OR for high HOMA-IR on the highest tertiles of serum lycopene and β-cryptoxanthin were 0.39 (95% CI: 0.21-0.73) and 0.51 (95% CI: 0.28-0.95), respectively.

CONCLUSIONS

The serum antioxidant carotenoids were inversely associated with HOMA-estimated insulin resistance in non-diabetic subjects.