Metabolic and hormonal effects of caffeine: randomized, double-blind, placebo-controlled crossover trial

Tea consumption and risk of type 2 diabetes: a meta-analysis of cohort studies

BACKGROUND

Tea consumption has been extensively studied in relation to various diseases, several epidemiologic studies have been performed to investigate the association of tea consumption with type 2 diabetes; however, the results of these studies were not entirely consistent.

OBJECTIVE

To conduct a meta-analysis of studies that assessed the association of tea consumption and the risk of type 2 diabetes.

RESEARCH DESIGN AND METHODS

We performed a systematic literature search through November 2008 in PUBMED, MEDLINE, EMBASE, and Cochrane Database of Systematic Reviews. The search was limited to English-language studies. Studies were excluded if they were type 1 diabetes, animal studies. Nine cohort studies were identified by two authors, and summary relative risks (RRs) were calculated using a random-effects model.

RESULTS

We identified nine cohort studies, including 324,141 participants and 11,400 incident cases of type 2 diabetes with follow-up ranging from 5 to 18 years. The summary adjusted RR did not show that tea consumption was associated with a reduced type 2 diabetes risk (RR, 0.96; 95% confidence interval (CI), 0.92-1.01). Evidence from the results of our stratified analyses revealed that tea consumption > or =4 cups per day (RR, 0.8; 95% CI, 0.7-0.93) might play a role in the prevention of type 2 diabetes. However, no statistically significant association was observed for sex and the follow-up durations stratified between tea consumption and type 2 diabetes.

CONCLUSIONS

This meta-analysis indicates that tea consumption > or =4 cups per day may lower the risk of type 2 diabetes.

Coffee consumption and risk of type 2 diabetes, cardiovascular diseases, and cancer

Numerous epidemiological studies have evaluated the association between coffee consumption and risk of type 2 diabetes, coronary heart disease, and various cancers. This paper briefly reviews the evidence for a relation between coffee consumption and these conditions, with particular attention to methodological issues. Several early studies suggested that coffee consumption could result in a marked increase in risk of coronary heart disease and several types of cancer. However, more recent prospective cohort studies that are less prone to selection and information bias have not confirmed these findings. High consumption of unfiltered types of coffee, such as French press and boiled coffee, has been shown to increase low-density-lipoprotein-cholesterol concentrations. In addition, limiting caffeinated coffee intake during pregnancy seems a prudent choice. However, evidence has been accumulating that frequent consumption of coffee may reduce risk of type 2 diabetes and liver cancer. Further experimental studies are warranted to elucidate the underlying mechanisms and possibly identify the components in coffee that are responsible for these putative effects. In sum, the currently available evidence on coffee and risk of cardiovascular diseases and cancer is largely reassuring, and suggests that, for the general population, addressing other health-related behaviors has priority for the prevention of chronic diseases.

Why do we respond so differently? Reviewing determinants of human salivary cortisol responses to challenge

Stress and stress-related health impairments are major problems in human life and elucidating the biological pathways linking stress and disease is of substantial importance. However, the identification of mechanisms underlying a dysregulation of major components of the stress response system is, particularly in humans, a very challenging task. Salivary cortisol responses to diverse acute challenge paradigms show large intra- and interindividual variability. In order to uncover mechanisms mediating stress-related disorders and to potentially develop new therapeutic strategies, an extensive phenotyping of HPA axis stress responses is essential. Such a research agenda depends on substantial knowledge of moderating and intervening variables that affect cortisol responses to different stressors and stimuli. The aim of this report is, therefore, to provide a comprehensive summary of important determinants of, in particular, human salivary cortisol responses to different kinds of laboratory stimuli including acute psychosocial stress as well as pharmacological provocation procedures. This overview demonstrates the role of age and gender, endogenous and exogenous sex steroid levels, pregnancy, lactation and breast-feeding, smoking, coffee and alcohol consumption as well as dietary energy supply in salivary cortisol responses to acute stress. Furthermore, it briefly summarizes current knowledge of the role of genetic factors and methodological issues in terms of habituation to repeated psychosocial stress exposures and time of testing as well as psychological factors, that have been shown to be associated with salivary cortisol responses like early life experiences, social factors, psychological interventions, personality as well as acute subjective-psychological stress responses and finally states of chronic stress and psychopathology.

ATM protein kinase mediates full activation of Akt and regulates glucose transporter 4 translocation by insulin in muscle cells

Ataxia-telangiectasia (A-T) is an autosomal recessive disorder characterized by cerebellar ataxia and oculocutaneous telangiectasias. Patients with A-T also have high incidences of type 2 diabetes mellitus. The gene mutated in this disease, ATM (A-T, mutated), encodes a protein kinase. Previous studies have demonstrated that cytoplasmic ATM is an insulin-responsive protein and a major upstream activator of Akt following insulin treatment. To further investigate the function of ATM in insulin signal transduction, insulin resistance was induced in rats by feeding them a high-fat diet. Muscle tissue of rats with insulin resistance had both dramatically reduced ATM levels and substantially decreased Akt phosphorylation at Ser473 in comparison to that of regular chow-fed controls. The decreased ATM expression suggests that ATM is involved in the development of insulin resistance through down-regulation of Akt activity. The role of ATM in activation of Akt was further confirmed in mouse embryonic fibroblast (MEF) A29 (ATM+/+) and A38 (ATM-/-) cells. In addition, insulin-mediated Akt phosphorylation in mouse L6 muscle cells was greatly reduced by KU-55933, a specific inhibitor of ATM. A 2-deoxyglucose incorporation assay showed that this inhibitor also caused a significant reduction in insulin-mediated glucose uptake in L6 cells. An immunofluorescence experiment demonstrated that in L6 cells transfected with wild-type (WT) ATM, insulin caused a dramatic increase of the cell surface glucose transporter 4 (GLUT4), while in cells transfected with kinase-dead (KD) ATM, translocation of GLUT4 to the cell surface in response to insulin was markedly inhibited.

An association between the methylenetetrahydrofolate reductase (MTHFR) C677T mutation and inflammation markers related to cardiovascular disease

BACKGROUND

Prospective studies have identified many markers of systemic inflammation that are powerful predictors of future cardiovascular events. The methylenetetrahydrofolate reductase (MTHFR) C677T genotype, a common polymorphism that induces hyperhomocysteinaemia, has been proposed as a genetic risk factor for cardiovascular disease. In this work, we evaluated the relationship between the levels of inflammation markers and MTHFR genotype among cardiovascular disease free subjects of the ATTICA study.

METHODS

During 2001-2002, we randomly enrolled for genetic evaluation 574 subjects from Attica region, Greece. In this work, we investigated demographic, lifestyle, clinical, biochemical and genetic information from 322 men (46+/-13 years) and 252 women (45+/-14 years). Among other characteristics, we measured various inflammatory markers levels in relation to C677T MTHFR genotype distribution.

RESULTS

The MTHFR genotypes distribution was: homozygous normal (CC) genotype, 41%; heterozygous (CT), 48%; and homozygous mutant (TT) genotype, 11%. C-reactive protein (CRA), fibrinogen, white blood cell (WBC) counts and amyloid-a levels were higher in TT compared to CC and CT genotypes (p<0.01), in both genders, even after controlling for various potential confounders.

CONCLUSION

The observed association between markers of systemic inflammation with MTHFR genotype may state a hypothesis for a common pathobiological mechanism between inflammation process and MTHFR, which is a key enzyme in homocysteine (Hcy) metabolism.