Vitamin E and risk of type 2 diabetes in the women's health study randomized controlled trial

Mediterranean diet and cognitive function in older age

BACKGROUND

Adherence to a Mediterranean diet may help prevent cognitive decline in older age, but studies are limited. We examined the association of adherence to the Mediterranean diet with cognitive function and decline.

METHODS

We included 6174 participants, aged 65+ years, from the cognitive substudy of the Women's Health Study. Women provided dietary information in 1998 and completed a cognitive battery 5 years later, followed by two assessments at 2-year intervals. The primary outcomes were composite scores of global cognition and verbal memory. The alternate Mediterranean diet adherence nine-point score was constructed based on intakes of vegetables, fruits, legumes, whole grains, nuts, fish, red and processed meats, moderate alcohol, and the ratio of monounsaturated-to-saturated fats.

RESULTS

After multivariable adjustment, the alternate Mediterranean diet score was not associated with trajectories of repeated cognitive scores (P for score quintiles medians-x-time interaction = 0.26 for global cognition and 0.40 for verbal memory), nor with overall global cognition and verbal memory at older ages, assessed by averaging the three cognitive measures (P trend = 0.63 and 0.44, respectively). Among alternate Mediterranean diet components, a higher monounsaturated-to-saturated fats ratio was associated with more favorable cognitive trajectories (P for ratio quintiles medians-x-time = 0.03 for global cognition and 0.05 for verbal memory). Greater whole grain intake was not associated with cognitive trajectories but was related to better averaged global cognition (P trend = 0.02).

CONCLUSIONS

In this large study of older women, we observed no association of the Mediterranean diet with cognitive decline. Relations between individual Mediterranean diet components, particularly whole grains, and cognitive function merit further study.

Oxidative stress in diabetes: implications for vascular and other complications

In recent decades, oxidative stress has become a focus of interest in most biomedical disciplines and many types of clinical research. Increasing evidence shows that oxidative stress is associated with the pathogenesis of diabetes, obesity, cancer, ageing, inflammation, neurodegenerative disorders, hypertension, apoptosis, cardiovascular diseases, and heart failure. Based on these studies, an emerging concept is that oxidative stress is the “final common pathway” through which the risk factors for several diseases exert their deleterious effects. Oxidative stress causes a complex dysregulation of cell metabolism and cell–cell homeostasis; in particular, oxidative stress plays a key role in the pathogenesis of insulin resistance and β-cell dysfunction. These are the two most relevant mechanisms in the pathophysiology of type 2 diabetes and its vascular complications, the leading cause of death in diabetic patients.

Modulation of endoplasmic reticulum chaperone GRP78 by high glucose in hippocampus of streptozotocin-induced diabetic mice and C6 astrocytic cells

Diabetes mellitus is known to increase the risk of neurodegeneration, and both diseases are reported to be linked to dysfunction of endoplasmic reticulum (ER). Astrocytes are important in the defense mechanism of central nervous system (CNS), with great ability of tolerating accumulation of toxic substances and sensitivity in Ca(2+) homeostasis which are two key functions of ER. Here, we investigated the modulation of the glucose-regulated protein 78 (GRP78) in streptozotocin (STZ)-induced diabetic mice and C6 cells cultured in high glucose condition. Our results showed that more reactive astrocytes were presented in the hippocampus of STZ-induced diabetic mice. Simultaneously, decrease of GRP78 expression was found in the astrocytes of diabetic mice hippocampus. In in vitro study, C6 cells were treated with high glucose to investigate the role of high glucose in GRP78 modulation in astrocytic cells. GRP78 as well as other chaperones like GRP94, calreticulin and calnexin, transcription levels were down-regulated after high glucose treatment. Also C6 cells challenged with 48h high glucose were activated, as indicated by increased level of glial fibrillary acidic protein (GFAP). Activated C6 cells simultaneously exhibited significant decrease of GRP78 level and was followed by reduced phosphorylation of Akt. Moreover, unfolded protein response was induced as an early event, which was marked by the induction of CHOP with high glucose treatment, followed by the reduction of GRP78 after 48h. Finally, the upsurge of ROS production was found in high glucose treated C6 cells and chelation of ROS could partially restore the GRP78 expression. Taken together, these data provide evidences that high glucose induced astrocytic activation in both in vivo and in vitro diabetic models, in which modulation of GRP78 would be an important event in this activation.

Validity of diabetes self-reports in the Saku diabetes study

BACKGROUND

Diabetes is an important risk factor for cardiovascular disease, certain types of cancer, and death, and self-reports are one of the most convenient methods for ascertaining diabetes status. We evaluated the validity of diabetes self-reports among Japanese who participated in a health checkup.

METHODS

Self-reported diabetes was cross-sectionally compared with confirmed diabetes among 2535 participants aged 28 to 85 years in the Saku cohort study. Confirmed diabetes was defined as the presence of at least 1 of the following: fasting plasma glucose (FPG) level of 126 mg/dL or higher, 2-hour post-load glucose (2-hPG) level of 200 mg/dL or higher after a 75-gram oral glucose tolerance test, glycated hemoglobin (HbA1c) level of 6.5% or higher, or treatment with hypoglycemic medication(s).

RESULTS

Of the 251 participants with self-reported diabetes, 121 were taking hypoglycemic medication(s) and an additional 69 were classified as having diabetes. Of the 2284 participants who did not self-report diabetes, 80 were classified as having diabetes. These data yielded a sensitivity of 70.4%, a specificity of 97.3%, a positive predictive value of 75.7%, and a negative predictive value of 96.5%. The frequency of participants with undiagnosed diabetes was 3.0%. Of these, 64.2% had FPG within the normal range and were diagnosed by 2-hPG and/or HbA1c.

CONCLUSIONS

Our findings provide additional support for the use of self-reported diabetes as a measure of diabetes in epidemiologic studies performed in similar settings in Japan if biomarker-based diagnosis is difficult.

Effect of antioxidant vitamin supplementation on cardiovascular outcomes: a meta-analysis of randomized controlled trials

BACKGROUND

Antioxidant vitamin (vitamin E, beta-carotene, and vitamin C) are widely used for preventing major cardiovascular outcomes. However, the effect of antioxidant vitamin on cardiovascular events remains unclear.

METHODOLOGY AND PRINCIPAL FINDINGS

We searched PubMed, EmBase, the Cochrane Central Register of Controlled Trials, and the proceedings of major conferences for relevant literature. Eligible studies were randomized controlled trials that reported on the effects of antioxidant vitamin on cardiovascular outcomes as compared to placebo. Outcomes analyzed were major cardiovascular events, myocardial infarction, stroke, cardiac death, total death, and any possible adverse events. We used the I(2) statistic to measure heterogeneity between trials and calculated risk estimates for cardiovascular outcomes with random-effect meta-analysis. Independent extraction was performed by two reviewers and consensus was reached. Of 293 identified studies, we included 15 trials reporting data on 188209 participants. These studies reported 12749 major cardiovascular events, 6699 myocardial infarction, 3749 strokes, 14122 total death, and 5980 cardiac deaths. Overall, antioxidant vitamin supplementation as compared to placebo had no effect on major cardiovascular events (RR, 1.00; 95%CI, 0.96-1.03), myocardial infarction (RR, 0.98; 95%CI, 0.92-1.04), stroke (RR, 0.99; 95%CI, 0.93-1.05), total death (RR, 1.03; 95%CI, 0.98-1.07), cardiac death (RR, 1.02; 95%CI, 0.97-1.07), revascularization (RR, 1.00; 95%CI, 0.95-1.05), total CHD (RR, 0.96; 95%CI, 0.87-1.05), angina (RR, 0.98; 95%CI, 0.90-1.07), and congestive heart failure (RR, 1.07; 95%CI, 0.96 to 1.19).

CONCLUSION/SIGNIFICANCE

Antioxidant vitamin supplementation has no effect on the incidence of major cardiovascular events, myocardial infarction, stroke, total death, and cardiac death.

Diabetic nephropathy and antioxidants

CONTEXT

Oxidative stress has crucial role in pathogenesis of diabetic nephropathy (DN). Despite satisfactory results from antioxidant therapy in rodent, antioxidant therapy showed conflicting results in combat with DN in diabetic patients.

EVIDENCE ACQUISITIONS

Directory of Open Access Journals (DOAJ), Google Scholar,Pubmed (NLM), LISTA (EBSCO) and Web of Science have been searched.

RESULTS

Treatment of DN in human are insufficient with rennin angiotensin system (RAS) blockers, so additional agent ought to combine with this management. Meanwhile based on DN pathogenesis and evidences in experimental and human researches, the antioxidants are the best candidate. New multi-property antioxidants may be improved human DN that show high power antioxidant capacity, long half-life time, high permeability to mitochondrion, improve body antioxidants enzymes activity and anti-inflammatory effects.

CONCLUSIONS

Based on this review and our studies on diabetic rats, rosmarinic acid a multi-property antioxidant may be useful in DN patients, but of course, needs to be proven in clinical trials studies.

Dietary fat types and 4-year cognitive change in community-dwelling older women

OBJECTIVE

A study was undertaken to relate dietary fat types to cognitive change in healthy community-based elders.

METHODS

Among 6,183 older participants in the Women's Health Study, we related intake of major fatty acids (saturated [SFA], monounsaturated [MUFA], total polyunsaturated [PUFA], trans-unsaturated) to late-life cognitive trajectory. Serial cognitive testing, conducted over 4 years, began 5 years after dietary assessment. Primary outcomes were global cognition (averaging tests of general cognition, verbal memory, and semantic fluency) and verbal memory (averaging tests of recall). We used analyses of response profiles and logistic regression to estimate multivariate-adjusted differences in cognitive trajectory and risk of worst cognitive change (worst 10%) by fat intake.

RESULTS

Higher SFA intake was associated with worse global cognitive (p for linear trend = 0.008) and verbal memory (p for linear trend = 0.01) trajectories. There was a higher risk of worst cognitive change, comparing highest versus lowest SFA quintiles; the multivariate-adjusted odds ratio (OR) with 95% confidence interval (CI) was 1.64 (1.04-2.58) for global cognition and 1.65 (1.04-2.61) for verbal memory. By contrast, higher MUFA intake was related to better global cognitive (p for linear trend < 0.001) and verbal memory (p for linear trend = 0.009) trajectories, and lower OR (95% CI) of worst cognitive change in global cognition (0.52 [0.31-0.88]) and verbal memory (0.56 [0.34-0.94]). Total fat, PUFA, and trans-fat intakes were not associated with cognitive trajectory.

INTERPRETATION

Higher SFA intake was associated with worse global cognitive and verbal memory trajectories, whereas higher MUFA intake was related to better trajectories. Thus, different consumption levels of the major specific fat types, rather than total fat intake itself, appeared to influence cognitive aging.

Role of coffee in modulation of diabetes risk

Coffee consumption has been associated with a lower risk of type 2 diabetes. This association does not depend on race, gender, geographic distribution of the study populations, or the type of coffee consumed (i.e., caffeinated or decaffeinated). This review discusses the strength of this relationship, examines the possibility that the pattern of coffee consumption could influence the association, and evaluates the possible relationship between coffee consumption and other risk factors associated with diabetes. Particular attention is paid to the identification, on the basis of the scientific evidence, of the possible mechanisms by which coffee components might affect diabetes development, especially in light of the paradoxical effect of caffeine on glucose metabolism. In addition to the role of coffee in reducing the risk of developing type 2 diabetes, the possible role of coffee in the course of the illness is explored. Finally, the possibility that coffee can also affect the risk of other forms of diabetes (e.g., type 1 diabetes and gestational diabetes) is examined.

Antioxidant supplements for prevention of mortality in healthy participants and patients with various diseases

BACKGROUND

Our systematic review has demonstrated that antioxidant supplements may increase mortality. We have now updated this review.

OBJECTIVES

To assess the beneficial and harmful effects of antioxidant supplements for prevention of mortality in adults.

SEARCH METHODS

We searched The Cochrane Library, MEDLINE, EMBASE, LILACS, the Science Citation Index Expanded, and Conference Proceedings Citation Index-Science to February 2011. We scanned bibliographies of relevant publications and asked pharmaceutical companies for additional trials.

SELECTION CRITERIA

We included all primary and secondary prevention randomised clinical trials on antioxidant supplements (beta-carotene, vitamin A, vitamin C, vitamin E, and selenium) versus placebo or no intervention.

DATA COLLECTION AND ANALYSIS

Three authors extracted data. Random-effects and fixed-effect model meta-analyses were conducted. Risk of bias was considered in order to minimise the risk of systematic errors. Trial sequential analyses were conducted to minimise the risk of random errors. Random-effects model meta-regression analyses were performed to assess sources of intertrial heterogeneity.

MAIN RESULTS

Seventy-eight randomised trials with 296,707 participants were included. Fifty-six trials including 244,056 participants had low risk of bias. Twenty-six trials included 215,900 healthy participants. Fifty-two trials included 80,807 participants with various diseases in a stable phase. The mean age was 63 years (range 18 to 103 years). The mean proportion of women was 46%. Of the 78 trials, 46 used the parallel-group design, 30 the factorial design, and 2 the cross-over design. All antioxidants were administered orally, either alone or in combination with vitamins, minerals, or other interventions. The duration of supplementation varied from 28 days to 12 years (mean duration 3 years; median duration 2 years). Overall, the antioxidant supplements had no significant effect on mortality in a random-effects model meta-analysis (21,484 dead/183,749 (11.7%) versus 11,479 dead/112,958 (10.2%); 78 trials, relative risk (RR) 1.02, 95% confidence interval (CI) 0.98 to 1.05) but significantly increased mortality in a fixed-effect model (RR 1.03, 95% CI 1.01 to 1.05). Heterogeneity was low with an I(2)- of 12%. In meta-regression analysis, the risk of bias and type of antioxidant supplement were the only significant predictors of intertrial heterogeneity. Meta-regression analysis did not find a significant difference in the estimated intervention effect in the primary prevention and the secondary prevention trials. In the 56 trials with a low risk of bias, the antioxidant supplements significantly increased mortality (18,833 dead/146,320 (12.9%) versus 10,320 dead/97,736 (10.6%); RR 1.04, 95% CI 1.01 to 1.07). This effect was confirmed by trial sequential analysis. Excluding factorial trials with potential confounding showed that 38 trials with low risk of bias demonstrated a significant increase in mortality (2822 dead/26,903 (10.5%) versus 2473 dead/26,052 (9.5%); RR 1.10, 95% CI 1.05 to 1.15). In trials with low risk of bias, beta-carotene (13,202 dead/96,003 (13.8%) versus 8556 dead/77,003 (11.1%); 26 trials, RR 1.05, 95% CI 1.01 to 1.09) and vitamin E (11,689 dead/97,523 (12.0%) versus 7561 dead/73,721 (10.3%); 46 trials, RR 1.03, 95% CI 1.00 to 1.05) significantly increased mortality, whereas vitamin A (3444 dead/24,596 (14.0%) versus 2249 dead/16,548 (13.6%); 12 trials, RR 1.07, 95% CI 0.97 to 1.18), vitamin C (3637 dead/36,659 (9.9%) versus 2717 dead/29,283 (9.3%); 29 trials, RR 1.02, 95% CI 0.98 to 1.07), and selenium (2670 dead/39,779 (6.7%) versus 1468 dead/22,961 (6.4%); 17 trials, RR 0.97, 95% CI 0.91 to 1.03) did not significantly affect mortality. In univariate meta-regression analysis, the dose of vitamin A was significantly associated with increased mortality (RR 1.0006, 95% CI 1.0002 to 1.001, P = 0.002).

AUTHORS' CONCLUSIONS

We found no evidence to support antioxidant supplements for primary or secondary prevention. Beta-carotene and vitamin E seem to increase mortality, and so may higher doses of vitamin A. Antioxidant supplements need to be considered as medicinal products and should undergo sufficient evaluation before marketing.

Socioeconomic status and incident type 2 diabetes mellitus: data from the Women's Health Study

Objectives

We prospectively examined whether socioeconomic status (SES) predicts incident type II diabetes (diabetes), a cardiovascular risk equivalent and burgeoning public health epidemic among women.

Methods

Participants include 23,992 women with Hb_A1c levels <6% and no CVD or diabetes at baseline followed from February 1993 to March 2007. SES was measured by education and income while diabetes was self-reported.

Results

Over 12.3 years of follow-up, 1,262 women developed diabetes. In age and race adjusted models, the relative risk of diabetes decreased with increasing education (<2 years of nursing, 2 to <4 years of nursing, bachelor's degree, master's degree, and doctorate: 1.0, 0.7 [95% Confidence Interval (CI), 0.6–0.8], 0.6 (95% CI, 0.5–0.7), 0.5 (95% CI, 0.4–0.6), 0.4 (95% CI, 0.3–0.5); p_trend<0.001). Adjustment for traditional and non-traditional cardiovascular risk factors attenuated this relationship (education: p_trend = 0.96). Similar associations were observed between income categories and diabetes.

Conclusion

Advanced education and increasing income were both inversely associated with incident diabetes even in this relatively well-educated cohort. This relationship was largely explained by behavioral factors, particularly body mass index.

Diabetes and cognitive decline in elderly African Americans: a 15-year follow-up study

BACKGROUND

Diabetes mellitus is associated with an increased risk for cognitive impairment and vascular factors seem to play a role in this relationship. In a sample involving elderly African Americans, we tested the hypothesis that diabetes accelerates cognitive decline and explored possible mediating mechanisms within a follow-up period of 15 years.

METHODS

A total of 1,702 subjects, of whom 441 had diabetes, were given the community screening interview for dementia to measure cognitive functioning at six different time points spread over a 15-year follow-up period. Mixed effects models with repeated measures were used to examine the association of diabetes and vascular risk factors with cognitive scores over time.

RESULTS

African American subjects with diabetes reported having a significant accelerated cognitive decline as compared with those without diabetes (P = .046), when controlling for basic demographics and baseline comorbid conditions (heart disease, hypertension, stroke, and depression). Adjusting for incident heart disease, and especially stroke, weakened this association (P = .098), thereby indicating a mediating effect of stroke on the association between diabetes and cognitive decline. However, when incident stroke was incorporated into the model, the effect for participants with diabetes increased greatly (P = .007).

CONCLUSIONS

Diabetes, mediated by cerebrovascular pathology, accelerates cognitive decline within a follow-up period of 15 years in a sample comprising African Americans.

Concentration-dependent dual effects of hydrogen peroxide on insulin signal transduction in H4IIEC hepatocytes

BACKGROUND

Oxidative stress induced by the accumulation of reactive oxygen species (ROS) has a causal role in the development of insulin resistance, whereas ROS themselves function as intracellular second messengers that promote insulin signal transduction. ROS can act both positively and negatively on insulin signaling, but the molecular mechanisms controlling these dual actions of ROS are not fully understood.

METHODOLOGY/PRINCIPAL FINDINGS

Here, we directly treated H4IIEC hepatocytes with hydrogen peroxide (H2O2), a representative membrane-permeable oxidant and the most abundant ROS in cells, to identify the key factors determining whether ROS impair or enhance intracellular insulin signaling. Treatment with high concentrations of H2O2 (25-50 µM) for 3 h reduced insulin-stimulated Akt phosphorylation, and increased the phosphorylation of both JNK and its substrate c-Jun. In contrast, lower concentrations of H2O2 (5-10 µM) enhanced insulin-stimulated phosphorylation of Akt. Moreover, lower concentrations suppressed PTP1B activity, suggesting that JNK and phosphatases such as PTP1B may play roles in determining the thresholds for the diametrical effects of H2O2 on cellular insulin signaling. Pretreatment with antioxidant N-acetyl-L-cysteine (10 mM) canceled the signal-promoting action of low H2O2 (5 µM), and it canceled out further impairment of insulin of insulin signaling induced by high H₂O₂ (25 µM).

CONCLUSIONS/SIGNIFICANCE

Our results demonstrate that depending on its concentration, H2O2 can have the positive or negative effect on insulin signal transduction in H4IIEC hepatocytes, suggesting that the concentration of intracellular ROS may be a major factor in determining whether ROS impair or enhance insulin signaling.

Vitamin E and adiponectin: proposed mechanism for vitamin E-induced improvement in insulin sensitivity

Insulin resistance and type 2 diabetes have been treated with the PPARγ agonists thiazolidinediones, or TZDs, since the 1990s. One mechanism by which these drugs may work is through PPARγ-mediated upregulation of adiponectin, an endogenous adipokine that has been shown to increase insulin sensitivity. Interestingly, α- and γ-tocopherol, two vitamin E vitamers, have structural similarities to the TZDs and have also been linked to enhanced insulin sensitivity. A recent study identified a novel function of α- and γ-tocopherol in 3T3-L1 preadipocytes: upregulation of an endogenous ligand involved in activating PPARγ. This study also found that tocopherols dramatically enhanced adiponectin expression and that this effect was mediated through a PPARγ-dependent process. These findings illustrate a possible mechanistic link between vitamin E and insulin sensitivity.

Lifestyle interaction with fat mass and obesity-associated (FTO) genotype and risk of obesity in apparently healthy U.S. women

OBJECTIVE

Variation in the fat mass and obesity-associated (FTO) gene is associated with obesity. The extent to which separate and combined effects of physical activity and caloric intake modify this association remains unclear.

RESEARCH DESIGN AND METHODS

FTO polymorphism rs8050136 was measured, and physical activity, caloric intake, and anthropometrics were self-reported in 21,675 apparently healthy Caucasian women.

RESULTS

The effect of the risk allele (A) on BMI was larger among inactive or higher intake women, with additive effects of inactivity and high intake on the associated genetic risk. Specifically, each A allele was associated with mean BMI difference of +0.73 (SE 0.08) kg/m(2) among inactive women (≤ median, 8.8 MET-hours/week), compared with +0.31 (0.06) kg/m(2), P < 0.0001, among active women (>8.8 MET-hours/week). Similarly, each A allele was associated with mean BMI difference of +0.65 (0.07) among high intake women (>median, 1,679 kcals/day), compared with +0.38 (0.07) kg/m(2), P = 0.005, among low intake women (≤ 1,679 kcals/day). Among inactive/high intake women, each A allele was associated with mean BMI difference of +0.97 (0.11) kg/m(2) vs. +0.22 (0.08) kg/m(2) among inactive/low intake women, P < 0.0001. Among inactive/high intake women, each A allele carried increased risk of obesity (odds ratio 1.39, 95% CI 1.27-1.52) and diabetes (odds ratio 1.36, 95% CI 1.07-1.73).

CONCLUSIONS

In this study, lifestyle factors modified the genetic risk of FTO on obesity phenotypes, particularly among women who were both inactive and had high intake. Healthier lifestyle patterns blunted but did not completely eliminate the associated genetic risk.

Vitamins D, C, and E in the prevention of type 2 diabetes mellitus: modulation of inflammation and oxidative stress

The incidence of type 2 diabetes mellitus (T2DM) is increasing worldwide, and certain population subgroups are especially vulnerable to the disease. To reduce T2DM risk and progression at the population level, preventative strategies are needed that can be implemented on a population-wide scale with minimal cost and effort. Chronic low-grade inflammation resulting from oxidative stress and imbalances in the innate immune system has been associated with obesity, metabolic syndrome, and insulin resistance – critical stages in the development and progression of T2DM. Therefore, inflammation may play a causal role in the pathogenesis of T2DM, and reducing it via modulation of oxidative stress and the innate immune response could lead to a status of improved insulin sensitivity and delayed disease onset. Dietary supplementation with anti-inflammatory and antioxidant nutritional factors, such as micronutrients, might present a novel strategy toward the prevention and control of T2DM at the population level. This review examines current knowledge linking oxidation, inflammatory signaling pathways, and vitamin supplementation or intake to the risk of T2DM. The concept that micronutrients, via attenuation of inflammation, could be employed as a novel preventive measure for T2DM is evaluated in the context of its relevance to public health.

Intake of antioxidants and risk of type 2 diabetes in a cohort of male smokers

BACKGROUND/OBJECTIVES

Oxidative stress may induce insulin resistance in peripheral tissues and impair insulin secretion from pancreatic β-cells. Antioxidants are suggested to decrease the risk of diabetes through reduction of oxidative stress. However, only a few studies exist on dietary antioxidants and the risk of type 2 diabetes. We investigated the association of dietary antioxidants with incident type 2 diabetes in the α-Tocopherol, β-Carotene Cancer Prevention Study cohort.

SUBJECT/METHODS

The study cohort included 29,133 male smokers aged 50-69 years. During a median follow-up of 10.2 years 660 incident cases of diabetes were observed among the 25,505 men with a completed baseline food frequency questionnaire.

RESULTS

Dietary α-tocopherol, β-tocopherol and β-tocotrienol were positively associated with the risk of diabetes when adjusted for age and supplementation (relative risk (RR) 1.17 (95% confidence interval (CI) 0.91-1.51) P for trend 0.02; RR 1.31 (95% CI 1.02-1.68) P for trend 0.01; RR 1.28 (95% CI 1.00-1.63) P for trend 0.01, respectively), but the association disappeared after multivariate adjustment (RR 0.92 (95% CI 0.71-1.19) P for trend 0.97; RR 1.06 (95% CI 0.82-1.36) P for trend 0.48; RR 1.04 (95% CI 0.80-1.35) P for trend 0.46, respectively). Other tocopherols and tocotrienols as well as vitamin C, carotenoids, flavonols and flavones had no association with risk of diabetes.

CONCLUSIONS

Dietary antioxidants were not associated with a decreased risk of incident diabetes in middle-aged male smokers.

Coffee and caffeine consumption in relation to sex hormone-binding globulin and risk of type 2 diabetes in postmenopausal women

OBJECTIVE

Coffee consumption has been inversely associated with type 2 diabetes risk, but its mechanisms are largely unknown. We aimed to examine whether plasma levels of sex hormones and sex hormone-binding globulin (SHBG) may account for the inverse association between coffee consumption and type 2 diabetes risk.

RESEARCH DESIGN AND METHODS

We conducted a case-control study nested in the prospective Women's Health Study (WHS). During a median follow-up of 10 years, 359 postmenopausal women with newly diagnosed type 2 diabetes were matched with 359 control subjects by age, race, duration of follow-up, and time of blood draw.

RESULTS

Caffeinated coffee was positively associated with SHBG but not with sex hormones. Multivariable-adjusted geometric mean levels of SHBG were 26.6 nmol/l among women consuming ≥4 cups/day of caffeinated coffee and 23.0 nmol/l among nondrinkers (P for trend = 0.01). In contrast, neither decaffeinated coffee nor tea was associated with SHBG or sex hormones. The multivariable-adjusted odds ratio (OR) of type 2 diabetes for women consuming ≥4 cups/day of caffeinated coffee compared with nondrinkers was 0.47 (95% CI 0.23-0.94; P for trend = 0.047). The association was largely attenuated after further adjusting for SHBG (OR 0.71 [95% CI 0.31-1.61]; P for trend = 0.47). In addition, carriers of rs6259 minor allele and noncarriers of rs6257 minor allele of SHBG gene consuming ≥2 cups/day of caffeinated coffee had lower risk of type 2 diabetes in directions corresponding to their associated SHBG.

CONCLUSIONS

Our findings suggest that SHBG may account for the inverse association between coffee consumption and type 2 diabetes risk among postmenopausal women.

Dietary omega-3 fatty acids and fish consumption and risk of type 2 diabetes

BACKGROUND

Although dietary omega-3 (n-3) fatty acids may confer some cardiovascular benefits, it is unclear whether these nutrients may also unfavorably affect risk of type 2 diabetes (T2D).

OBJECTIVE

We evaluated whether dietary omega-3 fatty acids and fish consumption were associated with increased risk of T2D.

DESIGN

This was a prospective study of 36,328 women (mean age: 54.6 y) who participated in the Women's Health Study and who were followed from 1992 to 2008. Incident T2D was self-reported and validated primarily through the collection of supplementary information from participants. Information on omega-3 and fish intakes was obtained by using a validated food-frequency questionnaire. We used Cox proportional hazard models to estimate adjusted relative risks.

RESULTS

During an average follow-up of 12.4 y, 2370 women developed T2D. Marine but not plant-based omega-3 fatty acids were positively associated with incident T2D. From the lowest to highest quintiles of marine omega-3 intake, the multivariable-adjusted hazard ratios (95% CIs) for T2D were 1.0 (referent), 1.17 (1.03, 1.33), 1.20 (1.05, 1.38), 1.46 (1.28, 1.66), and 1.44 (1.25, 1.65), respectively (P for trend < 0.0001). A similar association was observed with fish intake, but additional adjustment for docosahexaenoic acid led to the elimination of the association. The relation between marine omega-3 fatty acids and T2D was observed in hypertensive and nonhypertensive subjects and in women who reported infrequent fish consumption.

CONCLUSION

Our data suggest an increased risk of T2D with the intake of long-chain omega-3 fatty acids, especially with higher intakes (≥ 0.20 g omega-3/d or ≥ 2 servings of fish/d). The Women's Health Study was registered at clinicaltrials.gov as NCT00000479.

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.

Lipoprotein(a) and risk of type 2 diabetes

BACKGROUND

Previous studies have demonstrated that cardiovascular risk is higher with increased lipoprotein(a) [Lp(a)]. Whether Lp(a) concentration is related to type 2 diabetes is unclear.

METHODS

In 26 746 healthy US women (mean age 54.6 years), we prospectively examined baseline Lp(a) concentrations and incident type 2 diabetes (n = 1670) for a follow-up period of 13 years. We confirmed our findings in 9652 Danish men and women with prevalent diabetes (n = 419). Analyses were adjusted for risk factors that included age, race, smoking, hormone use, family history, blood pressure, body mass index, hemoglobin A(1c) (Hb A(1c)), C-reactive protein, and lipids.

RESULTS

Lp(a) was inversely associated with incident diabetes, with fully adjusted hazard ratios (HRs) and 95% CIs for quintiles 2-5 vs quintile 1 of 0.87 (0.75-1.01), 0.80 (0.68-0.93), 0.88 (0.76-1.02), and 0.78 (0.67-0.91); P for trend 0.002. The association was stronger in nonfasting women, for whom respective HRs were 0.79 (0.58-1.09), 0.78 (0.57-1.08), 0.66 (0.46-0.93), and 0.56 (0.40-0.80); P for trend 0.001; P for interaction with fasting status 0.002. When we used Lp(a) > or =10 mg/L and Hb A(1c) <5% as reference values, the adjusted HRs were 1.62 (0.91-2.89) for Lp(a) <10 mg/L and Hb A(1c) <5%, 3.50 (3.06-4.01) for Lp(a) > or =10 mg/L and Hb A(1c) 5%-<6.5%, and 5.36 (4.00-7.19) for Lp(a) <10 mg/L and Hb A(1c) 5%-<6.5%. Results were similar in nonfasting Danish men and women, for whom adjusted odds ratios were 0.75 (0.55-1.03), 0.64 (0.46-0.88), 0.74 (0.54-1.01), and 0.58 (0.42-0.79) for Lp(a) quintiles 2-5 vs quintile 1; P for trend 0.002.

CONCLUSIONS

Our results indicated that Lp(a) was associated inversely with risk of type 2 diabetes independently of risk factors, in contrast to prior findings of positive associations of Lp(a) with cardiovascular risk.

Health benefits of whole grain phytochemicals

A whole grain consists of the intact, ground, cracked, or flaked caryopsis, whose principal anatomical components--the starchy endosperm, germ, and bran--are present in the same relative proportions as they exist in the intact caryopsis. Whole grain food products can be intact, consisting of the original composition of bran, germ, and endosperm, throughout the entire lifetime of the product, or reconstituted, in which one or more of the original components of a whole grain is recombined to the relative proportion naturally occurring in the grain kernel. Increased consumption of whole grains has been associated with reduced risk of major chronic diseases including cardiovascular disease, type II diabetes, and some cancers. Whole grain foods offer a wide range of phytochemicals with health benefits that are only recently becoming recognized. The unique phytochemicals in whole grains are proposed to be responsible for the health benefits of whole grain consumption. In this paper, whole grain phytochemicals and the health benefits associated with their consumption are reviewed.

Lipoprotein particle size and concentration by nuclear magnetic resonance and incident type 2 diabetes in women

OBJECTIVE

Diabetic dyslipoproteinemia is characterized by low HDL cholesterol and high triglycerides. We examined the association of lipoprotein particle size and concentration measured by nuclear magnetic resonance (NMR) spectroscopy with clinical type 2 diabetes.

RESEARCH DESIGN AND METHODS

This was a prospective study of 26,836 initially healthy women followed for 13 years for incident type 2 diabetes (n = 1,687). Baseline lipids were measured directly and lipoprotein size and concentration by NMR. Cox regression models included nonlipid risk factors (age, race, smoking, exercise, education, menopause, blood pressure, BMI, family history, A1C, and C-reactive protein). NMR lipoproteins were also examined after further adjusting for standard lipids.

RESULTS

Incident diabetes was significantly associated with baseline HDL cholesterol, triglycerides, and NMR-measured size and concentration of LDL, IDL, HDL, and VLDL particles. The associations of these particles differed substantially by size. Small LDL(NMR) and small HDL(NMR) were positively associated with diabetes (quintile 5 vs. 1 [adjusted hazard ratios and 95% CIs], 4.04 [3.21-5.09] and 1.84 [1.54-2.19], respectively). By contrast, large LDL(NMR) and large HDL(NMR) were inversely associated (quintile 1 vs. 5, 2.50 [2.12-2.95] and 4.51 [3.68-5.52], respectively). For VLDL(NMR), large particles imparted higher risk than small particles (quintile 5 vs. 1, 3.11 [2.35-4.11] and 1.31 [1.10-1.55], respectively). Lipoprotein particle size remained significant after adjusting for standard lipids and nonlipid factors.

CONCLUSIONS

In this prospective study of women, NMR lipoprotein size and concentrations were associated with incident type 2 diabetes and remained significant after adjustment for established risk factors, including HDL cholesterol and triglycerides.

The role of vitamin E and oxidative stress in diabetes complications

Diabetes is a disease characterized by poor glycemic control for which risk of the type 2 form increases with age. A rise in blood glucose concentration causes increased oxidative stress which contributes to the development and progression of diabetes-associated complications. Studies have shown that primary antioxidants or genetic manipulation of antioxidant defenses can at least partially ameliorate this oxidative stress and consequentially, reduce severity of diabetic complications in animal models. Data from humans is less clear and will be summarized in this review. We highlight results from studies performed to investigate the role of vitamin E in preventing diabetes-induced oxidative damage in cell culture, animal models, and human participants, and summarize evidence testing whether this nutrient has an effect on outcomes related to the diabetic complications of nephropathy, retinopathy, and neuropathy. The most compelling evidence for an effect of vitamin E in diabetes is on protection against lipid peroxidation, whereas effects on protein and DNA oxidation are less pronounced. More studies are required to make definitive conclusions about the effect of vitamin E treatment on diabetes complications in human subjects.

Physical activity, body mass index, and diabetes risk in men: a prospective study

OBJECTIVE

Physical activity has been associated with lower diabetes risk, but several prospective studies among women found that activity only slightly attenuated the diabetes risk associated with high body mass index (BMI). We investigated the independent and joint associations between vigorous activity and BMI on diabetes risk in men.

METHODS

This was a prospective cohort design within the Physicians' Health Study, using Cox proportional hazards models to calculate hazard ratios (HRs) and 95% confidence intervals (CIs) of incident diabetes in 20,757 men without diabetes at baseline. Models were based on self-reported BMI and exercise frequency at baseline, first separately and then with a 6-category joint variable combining World Health Organization BMI category (normal/overweight/obese) with activity status (active/inactive) using weekly vigorous activity as the threshold.

RESULTS

After a median follow-up of 23.1 years, there were 1836 cases of incident diabetes. Compared with active participants with normal BMIs, active but overweight and obese men had multivariable-adjusted HRs of 2.39 (95% CI, 2.11-2.71) and 6.22 (95% CI, 5.12-7.56). Inactive men with normal, overweight, or obese BMIs had multivariable-adjusted HRs of 1.41 (95% CI, 1.19-1.67), 3.14 (95% CI, 2.73-3.62), and 6.57 (95% CI, 5.25-8.21).

CONCLUSION

Active men with normal and overweight BMIs had lower diabetes hazards than their inactive counterparts, but no difference by weekly activity was seen in obese men. Elevated BMI is a key driver of diabetes risk, with relatively modest attenuation by activity.

Understanding the role of diet in type 2 diabetes prevention

The number of people with type 2 diabetes is increasing at an alarming rate. Almost 4% of the UK population currently have diagnosed diabetes. Non-modifiable risk factors for diabetes include genetic predisposition, some black and ethnic minority groups and increasing age. Type 2 diabetes, (formally known as maturity onset diabetes), used to be a condition affecting adults only, although due to the increasing levels of obesity, it is now being diagnosed in young people and children. A healthy diet and lifestyle can help to prevent or delay the development of type 2 diabetes. In particular, strategies to reduce obesity will have a beneficial effect on the prevalence of type 2 diabetes, as excess adiposity (particularly central adiposity) is a strong risk factor for the condition. Dietary measures to reduce the risk of coronary heart disease will also help prevent diabetes. Diets low in fat (particularly saturated fat), and high in fibre and complex carbohydrates are effective in reducing the risk of developing diabetes. Good quality evidence from trials is required to determine the role of specific micronutrients in diabetes prevention.

Reactive oxygen species, reactive nitrogen species and antioxidants in etiopathogenesis of diabetes mellitus type-2

Diabetes mellitus type-2 (DMT-2) is a hyperglycemic syndrome with several characteristic features. It continues to rise unabatedly in all pockets of the world, parallels with affluence and can be controlled but not cured. It has a definite involvement of genetic component but environmental factors play overwhelmingly dominant role in etiopathogenesis. Insulin resistance (IR) and obesity are singular instigators of DMT-2. The various events cause critical defects in insulin signaling cascade followed by beta-cell dysfunction. Over a period of time, numerous other metabolic aberrations develop, resulting in diabetic complications which could be both vascular (cardiovascular complications, nephropathy, neuropathy, retinopathy and embryopathy) or a-vascular (cataract and glaucoma etc). It has been proposed that all these abnormal events are initiated or activated by a common mechanism of superoxide anion, which is accompanied with generation of a variety of reactive oxygen species (ROS), reactive nitrogen specie (RNS) and resultant heightened oxidative stress (OS). Provoked OS causes IR and altered gene expressions. Hyperglycemia induces OS through multiple routes: a)stimulated polyol pathway where in ≤ 30% glucose can be diverted to sorbitol and fructose, b)increased transcription of genes for proinflammatory cytokines and plasminogen activator inhibitor-1 (PAI-1) c) activation of protein kinase-C (PKC) leading to several molecular changes d)increased synthesis of Advanced Glycation End Products (AGEs) e)changes in a receptor far AGEs and f) autooxidation of glucose with formation of ketoimines and AGEs. All these processes are accompanied with alteration in redox status, ROS, RNS and OS which trigger DMT-2 and its complications. Initial hurriedly planned and executed experimental and clinical studies showed promising results of antioxidant therapies, but recent studies indicate that excess intake/supplement may have adverse outcomes including increased mortality. It is advocated that antioxidants should be given only if preexisting deficiency is present. Selection of antioxidant is another important aspect. Lastly but most importantly the impact of OS is not obligatory but facultative. As such only those diabetic patients will be benefited by antioxidant therapies that have impelling punch of prooxidants.

Sex hormone-binding globulin and risk of type 2 diabetes in women and men

BACKGROUND

Circulating sex hormone-binding globulin levels are inversely associated with insulin resistance, but whether these levels can predict the risk of developing type 2 diabetes is uncertain.

METHODS

We performed a nested case-control study of postmenopausal women in the Women's Health Study who were not using hormone therapy (359 with newly diagnosed type 2 diabetes and 359 controls). Plasma levels of sex hormone-binding globulin were measured; two polymorphisms of the gene encoding sex hormone-binding globulin, SHBG, that were robustly associated with the protein levels were genotyped and applied in mendelian randomization analyses. We then conducted a replication study in an independent cohort of men from the Physicians' Health Study II (170 with newly diagnosed type 2 diabetes and 170 controls).

RESULTS

Among women, higher plasma levels of sex hormone-binding globulin were prospectively associated with a lower risk of type 2 diabetes: multivariable odds ratios were 1.00 for the first (lowest) quartile of plasma levels, 0.16 (95% confidence interval [CI], 0.08 to 0.33) for the second quartile, 0.04 (95% CI, 0.01 to 0.12) for the third quartile, and 0.09 (95% CI, 0.03 to 0.21) for the fourth (highest) quartile (P<0.001 for trend). These prospective associations were replicated among men (odds ratio for the highest quartile of plasma levels vs. the lowest quartile, 0.10; 95% CI, 0.03 to 0.36; P<0.001 for trend). As compared with homozygotes of the respective wild-type allele, carriers of a variant allele of the SHBG single-nucleotide polymorphism (SNP) rs6259 had 10% higher sex hormone-binding globulin levels (P=0.005), and carriers of an rs6257 variant had 10% lower plasma levels (P=0.004); variants of both SNPs were also associated with a risk of type 2 diabetes in directions corresponding to their associated sex hormone-binding globulin levels. In mendelian randomization analyses, the predicted odds ratio of type 2 diabetes per standard-deviation increase in the plasma level of sex hormone-binding globulin was 0.28 (95% CI, 0.13 to 0.58) among women and 0.29 (95% CI, 0.15 to 0.58) among men, a finding that suggests that sex hormone-binding globulin may have a causal role in the risk of type 2 diabetes.

CONCLUSIONS

Low circulating levels of sex hormone-binding globulin are a strong predictor of the risk of type 2 diabetes in women and men. The clinical usefulness of both SHBG genotypes and plasma levels in stratification and intervention for the risk of type 2 diabetes warrants further examination.

Reactive oxygen-derived free radicals are key to the endothelial dysfunction of diabetes

Vascular complications are an important pathological issue in diabetes that lead to the further functional deterioration of several organs. The balance between endothelium-dependent relaxing factors and endothelium-dependent contracting factors (EDCFs) is crucial in controlling local vascular tone and function under normal conditions. Diabetic endothelial dysfunction is characterized by reduced endothelium-dependent relaxations and/or enhanced endothelium-dependent contractions. Elevated levels of oxygen-derived free radicals are the initial source of endothelial dysfunction in diabetes. Oxygen-derived free radicals not only reduce nitric oxide bioavailability, but also facilitate the production and/or action of EDCFs. Thus, the endothelial balance tips towards vasoconstrictor responses over the course of diabetes.

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.

Vitaminas e minerais com propriedades antioxidantes e risco cardiometabólico: controvérsias e perspectivas

No processo celular de obtenção de energia, são gerados compostos chamados espécies reativas de oxigênio (ERO) que, em excesso, podem causar danos celulares. Estresse oxidativo resulta do desequilíbrio no estado de óxido-redução a favor da oxidação. Dos mecanismos de defesa antioxidante, participam enzimas endógenas e algumas vitaminas e minerais. A vitamina E encontra-se no plasma e na partícula de LDL, protegendo lipídeos da oxidação. Estudos observacionais relataram associação inversa entre ingestão de vitamina E e risco cardiometabólico (RCM). Entretanto, ensaios clínicos não comprovaram a eficácia de sua suplementação nos desfechos cardiometabólicos. A vitamina C participa do sistema de regeneração da vitamina E, mantendo o potencial antioxidante plasmático. Dados sobre os benefícios de sua suplementação na redução do risco cardiometabólico são inconclusivos. A atividade antioxidante dos carotenoides é responsável, em parte, por seu papel protetor contra doenças cardiovasculares e cânceres. A suplementação desse nutriente também não trouxe resultados consistentes no que se refere à redução do RCM. A participação do zinco e do selênio na defesa antioxidante vem sendo estudada mais recentemente, mas a sua suplementação em indivíduos com níveis séricos normais e ingestão adequada na dieta desses minerais não parece ser necessária. De um modo geral, há muita controvérsia sobre o papel desses micronutrientes no RCM. Estudos epidemiológicos sugerem que o consumo de substâncias antioxidantes provenientes da dieta ou dietas ricas em frutas e hortaliças diminui o RCM. Mais estudos são necessários antes de se recomendar o uso de antioxidantes isolados na forma de suplementos para tal finalidade.

Antioxidants prevent health-promoting effects of physical exercise in humans

Exercise promotes longevity and ameliorates type 2 diabetes mellitus and insulin resistance. However, exercise also increases mitochondrial formation of presumably harmful reactive oxygen species (ROS). Antioxidants are widely used as supplements but whether they affect the health-promoting effects of exercise is unknown. We evaluated the effects of a combination of vitamin C (1000 mg/day) and vitamin E (400 IU/day) on insulin sensitivity as measured by glucose infusion rates (GIR) during a hyperinsulinemic, euglycemic clamp in previously untrained (n = 19) and pretrained (n = 20) healthy young men. Before and after a 4 week intervention of physical exercise, GIR was determined, and muscle biopsies for gene expression analyses as well as plasma samples were obtained to compare changes over baseline and potential influences of vitamins on exercise effects. Exercise increased parameters of insulin sensitivity (GIR and plasma adiponectin) only in the absence of antioxidants in both previously untrained (P < 0.001) and pretrained (P < 0.001) individuals. This was paralleled by increased expression of ROS-sensitive transcriptional regulators of insulin sensitivity and ROS defense capacity, peroxisome-proliferator-activated receptor gamma (PPARgamma), and PPARgamma coactivators PGC1alpha and PGC1beta only in the absence of antioxidants (P < 0.001 for all). Molecular mediators of endogenous ROS defense (superoxide dismutases 1 and 2; glutathione peroxidase) were also induced by exercise, and this effect too was blocked by antioxidant supplementation. Consistent with the concept of mitohormesis, exercise-induced oxidative stress ameliorates insulin resistance and causes an adaptive response promoting endogenous antioxidant defense capacity. Supplementation with antioxidants may preclude these health-promoting effects of exercise in humans.

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.

Circulating levels of resistin and risk of type 2 diabetes in men and women: results from two prospective cohorts

OBJECTIVE

The purpose of this study was to investigate the role of circulating resistin levels in the development of type 2 diabetes using two prospective cohorts of well-characterized men and women.

RESEARCH DESIGN AND METHODS

We conducted two prospective case-control studies nested in the Women's Health Study (WHS) and Physicians' Health Study II (PHS II). In the WHS, during a median of 10-years of follow-up, 359 postmenopausal women, who were apparently healthy at baseline and later developed type 2 diabetes, were prospectively matched with 359 healthy control subjects. In the PHS II, with 8 years of total follow-up, 170 men, who were apparently healthy at baseline and later developed type 2 diabetes, were matched with 170 healthy control subjects. Control subjects were matched by age, race, and time of blood draw.

RESULTS

Resistin levels at baseline were significantly higher in women than in men (P = 0.003) and in case patients than in control subjects for both women (P < 0.001) and men (P = 0.07). After adjustment for matching factors, physical activity, alcohol intake, smoking, and family history of diabetes, the relative risk of type 2 diabetes comparing the highest to the lowest quartile of resistin in women was 2.22 ([95% CI 1.32-3.73]; Ptrend = 0.002). This association was attenuated after further adjustment for BMI (1.51 [0.86-2.65]; Ptrend = 0.20) or C-reactive protein (1.18 [0.68-2.07]; Ptrend = 0.60). A similar but weaker pattern was observed in men.

CONCLUSIONS

Elevated levels of circulating resistin were significantly related to increased risk of type 2 diabetes, which appears to be partially accounted for by adiposity and the inflammatory process.

Egg consumption and risk of type 2 diabetes in men and women

OBJECTIVE

Whereas limited and inconsistent findings have been reported on the relation between dietary cholesterol or egg consumption and fasting glucose, no previous study has examined the association between egg consumption and type 2 diabetes. This project sought to examine the relation between egg intake and the risk of type 2 diabetes in two large prospective cohorts.

RESEARCH DESIGN AND METHODS

In this prospective study, we used data from two completed randomized trials: 20,703 men from the Physicians' Health Study I (1982-2007) and 36,295 women from the Women's Health Study (1992-2007). Egg consumption was ascertained using questionnaires, and we used the Cox proportional hazard model to estimate relative risks of type 2 diabetes.

RESULTS

During mean follow-up of 20.0 years in men and 11.7 years in women, 1,921 men and 2,112 women developed type 2 diabetes. Compared with no egg consumption, multivariable adjusted hazard ratios for type 2 diabetes were 1.09 (95% CI 0.87-1.37), 1.09 (0.88-1.34), 1.18 (0.95-1.45), 1.46 (1.14-1.86), and 1.58 (1.25-2.01) for consumption of <1, 1, 2-4, 5-6, and > or =7 eggs/week, respectively, in men (P for trend <0.0001). Corresponding multivariable hazard ratios for women were 1.06 (0.92-1.22), 0.97 (0.83-1.12), 1.19 (1.03-1.38), 1.18 (0.88-1.58), and 1.77 (1.28-2.43), respectively (P for trend <0.0001).

CONCLUSIONS

These data suggest that high levels of egg consumption (daily) are associated with an increased risk of type 2 diabetes in men and women. Confirmation of these findings in other populations is warranted.

Serum and dietary beta-carotene and alpha-tocopherol and incidence of type 2 diabetes mellitus in a community-based study of Swedish men: report from the Uppsala Longitudinal Study of Adult Men (ULSAM) study

AIMS/HYPOTHESIS

To investigate the association of serum concentrations and dietary intake of beta-carotene and alpha-tocopherol with type 2 diabetes incidence.

METHODS

Serum beta-carotene, alpha-tocopherol, lifestyle factors (BMI, physical activity and smoking) and metabolic factors (insulin sensitivity [homeostasis model assessment], acute insulin response and impaired fasting glucose) were analysed in 846 50-year-old non-diabetic Swedish men (participants in the Uppsala Longitudinal Study of Adult Men). Diabetes was identified in 245 participants at reinvestigations after 10, 20 and 27 years. At the 20 year reinvestigation, dietary intake of beta-carotene and alpha-tocopherol, insulin sensitivity (euglycaemic-hyperinsulinaemic clamp) and insulin secretion (early insulin response in OGTT) were determined.

RESULTS

The highest tertile of serum beta-carotene at age 50 (>0.335 mumol/l) was associated with 59% lower risk of diabetes during follow-up compared with the lowest tertile (<0.210 mumol/l) after adjustment for lifestyle and metabolic factors (p < 0.01). The highest tertile of lipid-corrected serum alpha-tocopherol at age 50 (>3.67 mumol/mmol) was associated with 46% lower risk of diabetes compared with the lowest tertile (<3.25 mumol/mmol) independently of metabolic factors (p < 0.05). Moreover, lower serum beta-carotene and alpha-tocopherol concentrations were independently associated with impaired insulin sensitivity (p < 0.001), but not with early insulin response, in a subsample of non-diabetic individuals 20 years later. Dietary intake of beta-carotene and alpha-tocopherol independently predicted type 2 diabetes during 7 years of follow-up.

CONCLUSIONS/INTERPRETATION

Serum concentrations and dietary intakes of beta-carotene and alpha-tocopherol independently predicted insulin resistance and type 2 diabetes incidence during 27 years of follow-up in a community-based study of men. This result supports the importance of impaired antioxidant status for the development of insulin resistance and type 2 diabetes.

A randomized trial of low-dose aspirin in the prevention of clinical type 2 diabetes in women

OBJECTIVE

Subclinical inflammation is linked with the development of type 2 diabetes, and epidemiologic data suggest that this association may be stronger in women. Although small clinical studies have shown a prominent hypoglycemic effect of short-term high-dose aspirin, no randomized trials have directly evaluated the efficacy of aspirin in diabetes prevention at doses acceptable for use in routine clinical practice. We evaluated whether chronic low-dose aspirin prevents the development of clinical diabetes among initially healthy American women.

RESEARCH DESIGN AND METHODS

Subjects were enrolled in the Women's Health Study, a 10-year randomized double-blind, placebo-controlled trial of aspirin and vitamin E for primary prevention of cardiovascular disease and cancer. Between 1992 and 1995, 38,716 women aged > or =45 years and free of clinical diabetes were randomly assigned to either low-dose aspirin or placebo (median follow-up 10.2 years). Documented clinical type 2 diabetes was prospectively evaluated throughout the trial.

RESULTS

Among women randomly assigned to receive aspirin (n = 19,326) or placebo (n = 19,390), there was no statistically significant difference in the incidence of type 2 diabetes. There were 849 cases of diabetes in the aspirin group and 847 in the placebo group (rate ratio 1.01 [95% CI 0.91-1.11]). Stratification by diabetes risk factors including age, BMI, family history of diabetes, physical activity, A1C, and high-sensitivity C-reactive protein did not support a modulating effect of these variables. Analyses accounting for treatment duration and adherence similarly found no beneficial effects.

CONCLUSIONS

These data suggest that long-term low-dose aspirin does not prevent the development of clinical type 2 diabetes in initially healthy women.

Antioxidant effects and insulin resistance improvement of chromium combined with vitamin C and e supplementation for type 2 diabetes mellitus

To determine the effects of combined supplementation with chromium (Cr) and vitamins C and E on oxidative stress in type 2 diabetes, adult subjects with HbA1c >8.5%. Subjects (n = 30) in this randomized, double blind, placebo-control study were divided into three groups (placebo, Cr or Cr + C + E) on daily treatment. The Cr group received 1000 microg of Cr (as Cr yeast); the Cr + C + E group received Cr (1000 microg as Cr yeast) together with vitamins C (1000 mg) and E (800 IU); and, a control group received a placebo. Baseline plasma Cr levels were not significant differences comparing the supplementation and placebo groups. Thiobarbituric acid reactive substances (TBARS) and total antioxidative status (TAS) were also not significant different. Following the 6-month study period, the plasma TBARS levels, fasting glucose, HbA1c and insulin resistance were significantly decreased in the Cr and Cr + C + E groups, but not for the placebo group. Plasma TAS and glutathione peroxidase were significantly higher for Cr and Cr + C + E groups relative to the placebo group. These findings suggest that Cr supplementation alone and combined of Cr together with vitamins C and E was effective for minimization of oxidative stress and improvement of glucose metabolism in type 2 DM patients.

Renin-angiotensin and endothelial nitric oxide synthase gene polymorphisms are not associated with the risk of incident type 2 diabetes mellitus: a prospective cohort study

OBJECTIVE

The renin-angiotensin system and endothelial function have both been implicated in the pathogenesis of type 2 diabetes. The aim of this study was to assess the relationship between a set of well-characterized genetic variants of the renin-angiotensin system and the endothelial nitric oxide synthase (NOS3) gene and the incidence of type 2 diabetes.

DESIGN

Prospective cohort study.

SETTING

Women's Health Study, United States.

SUBJECTS

A total of 24,309 Caucasian women free of diabetes at baseline.

MAIN OUTCOME MEASURES

Six previously characterized single nucleotide polymorphisms (NOS3 rs1800779, NOS3 rs3918226, NOS3 rs1799983, ACE rs1799752, AGT rs699 and AGTR rs5186) were genotyped. Cox proportional-hazards models were constructed to compare the incidence of type 2 diabetes according to the different genotypes.

RESULTS

During a median follow-up of 10.2 years (interquartile range 9.6-10.6 years), 999 women developed type 2 diabetes. The age-adjusted incidence rates across the six genotypes were very similar, and ranged from 3.7 to 4.8 cases/1000 person-years of follow-up. The multivariable adjusted hazard ratios (95% confidence intervals) for rs1800779, rs3918226, rs1799983, rs1799752, rs699, and rs5186 were 1.01 (0.92-1.10), 1.09 (0.93-1.27), 0.95 (0.86-1.05), 1.04 (0.95-1.14), 1.08 (0.98-1.18), 1.01 (0.91-1.11), confirming the lack of association between the genotypes and incident type 2 diabetes. Stratification by body mass index revealed essentially unchanged results. Finally, there was no association between NOS3-haplotypes and incident type 2 diabetes.

CONCLUSION

We did not find an association between six well-characterized genetic polymorphisms of the renin-angiotensin system or the NOS3 gene and the occurrence of type 2 diabetes.

Lifestyle and Risk of Cardiovascular Disease and Type 2 Diabetes in Women: A Review of the Epidemiologic Evidence

Cardiovascular disease is the leading cause of death among both women and men in the United States, accounting for nearly half of all deaths and considerable morbidity. Type 2 diabetes is a major risk factor for cardiovascular disease and one that is particularly potent in women; its prevalence has increased dramatically in recent years. Epidemiologic data indicate that cardiovascular disease and type 2 diabetes share common risk factors and are largely preventable; indeed, findings from the Nurses' Health Study suggest that 74% of cardiovascular disease cases, 82% of coronary heart disease cases, and 91% of diabetes cases in women could be prevented by not smoking, engaging in regular physical activity, maintaining a healthy weight, eating healthier food, and drinking moderate amounts of alcohol. This article reviews lifestyle risk factors and preventive strategies for cardiovascular disease and type 2 diabetes among women.

Prospective study of coffee and tea consumption in relation to risk of type 2 diabetes mellitus among men and women: the Whitehall II study

At least fourteen cohort studies have documented an inverse association between coffee consumption and risk of type 2 diabetes. We examined the prospective association between coffee and tea consumption and the risk of type 2 diabetes mellitus among British men (n 4055) and women (n 1768) from the Whitehall II cohort. During 11.7 years follow-up there were a total of 387 incident cases of diabetes confirmed by self-report of doctor's diagnosis or glucose tolerance tests. Despite an inverse association between coffee intake and 2 h post-load glucose concentration at the baseline assessment, combined caffeinated and decaffeinated coffee (hazard ratio (HR) 0.80; 95 % CI 0.54, 1.18) or only decaffeinated coffee intake (HR 0.65; 95 % CI 0.36, 1.16) was not significantly associated with diabetes risk at follow-up after adjustment for possible confounders. There was an association between tea intake and diabetes (HR 0.66; 95 % CI 0.61, 1.22; P < 0.05) after adjustment for age, gender, ethnicity and social status, which was not robust to further adjustments. There was, however, an association between combined intake of tea and coffee (two or more cups per day of both beverage) and diabetes (HR 0.68; 95 % CI 0.46, 0.99; P < 0.05) after full adjustment. In conclusion, relatively moderate intake (more than three cups per day) of coffee and tea were not prospectively associated with incidence of type 2 diabetes although there was evidence of a combined effect. The limited range of exposure and beverage consumption according to socio-economic class may explain these conflicting findings.