Effects of Vitamin D Supplementation on Insulin Sensitivity and Secretion in Prediabetes

CONTEXT

Vitamin D regulates glucose homeostasis pathways, but effects of vitamin D supplementation on β-cell function remain unclear.

OBJECTIVE

To investigate the effects of vitamin D3 supplementation on insulin sensitivity and β-cell function.

METHODS

This is a prespecified secondary analysis of the Vitamin D and Type 2 Diabetes study. Overweight/obese adults at high risk for type 2 diabetes (prediabetes) were randomly treated with vitamin D3 4000 IU or matching placebo daily for 24 months.

MAIN OUTCOME

Disposition index (DI), as an estimate of β-cell function, was calculated as the product of Homeostasis Model Assessment 2 indices derived from C-peptide values (HOMA2%Scpep) and C-peptide response during the first 30 minutes of a 75-g oral glucose tolerance test (OGTT).

RESULTS

Mean age was 60.5 ± 9.8 years and body mass index was 31.9 ± 4.4 kg/m2. Mean serum 25(OH)D level increased from 27.9 ± 10.3 ng/mL at baseline to 54.9 ng/mL at 2 years in the vitamin D group and was unchanged (28.5 ± 10.0 ng/mL) in the placebo group. The baseline DI predicted incident diabetes independent of the intervention. In the entire cohort, there were no significant differences in changes in DI, HOMA2%Scpep, or C-peptide response between the 2 groups. Among participants with baseline 25(OH)D level <12 ng/mL, the mean percent differences for DI between the vitamin D and placebo groups was 8.5 (95% CI, 0.2-16.8).

CONCLUSIONS

Supplementation with vitamin D3 for 24 months did not improve an OGTT-derived index of β-cell function in people with prediabetes not selected based on baseline vitamin D status; however, there was benefit among those with very low baseline vitamin D status.

Intratrial Exposure to Vitamin D and New-Onset Diabetes Among Adults With Prediabetes: A Secondary Analysis From the Vitamin D and Type 2 Diabetes (D2d) Study

OBJECTIVE

Postrandomization biases may influence the estimate of efficacy of supplemental vitamin D in diabetes prevention trials. In the Vitamin D and Type 2 Diabetes (D2d) study, repeated measures of serum 25-hydroxyvitamin D [25(OH)D] level provided an opportunity to test whether intratrial vitamin D exposure affected diabetes risk and whether the effect was modified by trial assignment (vitamin D vs. placebo).

RESEARCH DESIGN AND METHODS

The D2d study compared the effect of daily supplementation with 100 μg (4,000 units) of vitamin D₃ versus placebo on new-onset diabetes in adults with prediabetes. Intratrial vitamin D exposure was calculated as the cumulative rolling mean of annual serum 25(OH)D measurements. Hazard ratios for diabetes among participants who had intratrial 25(OH)D levels of <50, 75-99, 100-124, and ≥125 nmol/L were compared with those with levels of 50-74 nmol/L (the range considered adequate by the National Academy of Medicine) in the entire cohort and by trial assignment.

RESULTS

There was an interaction of trial assignment with intratrial 25(OH)D level in predicting diabetes risk (interaction P = 0.018). The hazard ratio for diabetes for an increase of 25 nmol/L in intratrial 25(OH)D level was 0.75 (95% CI 0.68-0.82) among those assigned to vitamin D and 0.90 (0.80-1.02) among those assigned to placebo. The hazard ratios for diabetes among participants treated with vitamin D who maintained intratrial 25(OH)D levels of 100-124 and ≥125 nmol/L were 0.48 (0.29-0.80) and 0.29 (0.17-0.50), respectively, compared with those who maintained a level of 50-74 nmol/L.

CONCLUSIONS

Daily vitamin D supplementation to maintain a serum 25(OH)D level ≥100 nmol/L is a promising approach to reducing the risk of diabetes in adults with prediabetes.

Reproducibility of a prediabetes classification in a contemporary population

Aims

To assess whether meeting both fasting plasma glucose (FPG) and HbA1c criteria for prediabetes in people at high risk indicates with near certainty the presence of dysglycemia on repeat testing.

Methods

Observational study using data from Vitamin D and Type 2 Diabetes (D2d) study. HbA1c, FPG were measured at screening visit 1; FPG, HbA1c and 2 h plasma glucose (2hPG) measured at screening visit 2 (a median of 21 days later); participants classified as having normal glucose regulation (all 3 tests in normal range), prediabetes or diabetes (at least 1 of 3 tests in diabetes range). A predictive model was developed to estimate the probability of confirming dysglycemia and for detecting diabetes at screening visit 2 based on values of FPG and HbA1c at screening visit 1.

Results

Of 1271 participants who met both FPG and HbA1c criteria for prediabetes at screening visit 1, 98.6% exhibited dysglycemia (defined as prediabetes or diabetes) on repeat testing (84.5% were classified as having prediabetes, 14.1% were reclassified as having diabetes). Of those with diabetes, 62.6% were identified by 2hPG alone.

Conclusions

Combined measurement of FPG and HbA1c is a reliable and reproducible measure to identify presence of dysglycemia among people at high risk. A prediction model is provided to help clinicians decide whether an oral glucose tolerance test will provide value in detecting diabetes based on the 2hPG criterion.

Establishing an electronic health record-supported approach for outreach to and recruitment of persons at high risk of type 2 diabetes in clinical trials: The vitamin D and type 2 diabetes (D2d) study experience

AIMS

To establish recruitment approaches that leverage electronic health records in multicenter prediabetes/diabetes clinical trials and compare recruitment outcomes between electronic health record-supported and conventional recruitment methods.

METHODS

Observational analysis of recruitment approaches in the vitamin D and type 2 diabetes (D2d) study, a multicenter trial in participants with prediabetes. Outcomes were adoption of electronic health record-supported recruitment approaches by sites, number of participants screened, recruitment performance (proportion screened who were randomized), and characteristics of participants from electronic health record-supported versus non-electronic health record methods.

RESULTS

In total, 2423 participants were randomized: 1920 from electronic health record (mean age of 60 years, 41% women, 68% White) and 503 from non-electronic health record sources (mean age of 56.9 years, 58% women, 61% White). Electronic health record-supported recruitment was adopted by 21 of 22 sites. Electronic health record-supported recruitment was associated with more participants screened versus non-electronic health record methods (4969 vs 2166 participants screened), higher performance (38.6% vs 22.7%), and more randomizations (1918 vs 505). Participants recruited via electronic health record were older, included fewer women and minorities, and reported higher use of dietary supplements. Electronic health record-supported recruitment was incorporated in diverse clinical environments, engaging clinicians either at the individual or the healthcare system level.

CONCLUSION

Establishing electronic health record-supported recruitment approaches across a multicenter prediabetes/diabetes trial is feasible and can be adopted by diverse clinical environments.

Mixed Meal and Intravenous L-Arginine Tests Both Stimulate Incretin Release Across Glucose Tolerance in Man: Lack of Correlation with β Cell Function

BACKGROUND

The aims of this study were to 1. define the responses of glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP), glucagon, and peptide YY (PYY) to an oral meal and to intravenous L-arginine; and 2. examine correlation of enteroendocrine hormones with insulin secretion. We hypothesized a relationship between circulating incretin concentrations and insulin secretion.

METHODS

Subjects with normal glucose tolerance (NGT, n = 23), prediabetes (PDM, n = 17), or with type 2 diabetes (T2DM, n = 22) were studied twice, following a mixed test meal (470 kCal) (mixed meal tolerance test [MMTT]) or intravenous L-arginine (arginine maximal stimulation test [AST], 5 g). GLP-1 (total and active), PYY, GIP, glucagon, and β cell function were measured before and following each stimulus.

RESULTS

Baseline enteroendocrine hormones differed across the glucose tolerance (GT) spectrum, T2DM generally >NGT and PDM. In response to MMTT, total and active GLP-1, GIP, glucagon, and PYY increased in all populations. The incremental area-under-the-curve (0-120 min) of analytes like total GLP-1 were often higher in T2DM compared with NGT and PDM (35-51%; P < 0.05). At baseline glucose, L-arginine increased total and active GLP-1 and glucagon concentrations in all GT populations (all P < 0.05). As expected, the MMTT and AST provoked differential glucose, insulin, and C-peptide responses across GT populations. Baseline or stimulated enteroendocrine hormone concentrations did not consistently correlate with either measure of β cell function.

CONCLUSIONS/INTERPRETATION

Both MMTT and AST resulted in insulin and enteroendocrine hormone responses across GT populations without consistent correlation between release of incretins and insulin, which is in line with other published research. If a defect is in the enteroendocrine/β cell axis, it is probably reduced response to rather than diminished secretion of enteroendocrine hormones.

Baseline Characteristics of the Vitamin D and Type 2 Diabetes (D2d) Study: A Contemporary Prediabetes Cohort That Will Inform Diabetes Prevention Efforts

OBJECTIVE

To describe baseline characteristics of the Vitamin D and Type 2 Diabetes (D2d) study, the first large U.S. diabetes prevention clinical trial to apply current American Diabetes Association (ADA) criteria for prediabetes.

RESEARCH DESIGN AND METHODS

This is a multicenter (n = 22 sites), randomized, double-blind, placebo-controlled, primary prevention clinical trial testing effects of oral daily 4,000 IU cholecalciferol (D3) compared with placebo on incident diabetes in U.S. adults at risk for diabetes. Eligible participants were at risk for diabetes, defined as not meeting criteria for diabetes but meeting at least two 2010 ADA glycemic criteria for prediabetes: fasting plasma glucose (FPG) 100-125 mg/dL, 2-h postload glucose (2hPG) after a 75-g oral glucose load 140-199 mg/dL, and/or a hemoglobin A1c (HbA1c) 5.7-6.4% (39-46 mmol/mol).

RESULTS

A total of 2,423 participants (45% of whom were women and 33% nonwhite) were randomized to cholecalciferol or placebo. Mean (SD) age was 59 (9.9) years and BMI 32 (4.5) kg/m2. Thirty-five percent met all three prediabetes criteria, 49% met the FPG/HbA1c criteria only, 9.5% met the 2hPG/FPG criteria only, and 6.3% met the 2hPG/HbA1c criteria only. Black participants had the highest mean HbA1c and lowest FPG concentration compared with white, Asian, and other races (P < 0.01); 2hPG concentration did not differ among racial groups. When compared with previous prediabetes cohorts, the D2d cohort had lower mean 2hPG concentration but similar HbA1c and FPG concentrations.

CONCLUSIONS

D2d will establish whether vitamin D supplementation lowers risk of diabetes and will inform about the natural history of prediabetes per contemporary ADA criteria.

Outpatient versus inpatient mixed meal tolerance and arginine stimulation testing yields comparable measures of variability for assessment of beta cell function

Standard practice to minimize variability in beta cell function (BCF) measurement is to test in inpatient (IP) settings. IP testing strains trial subjects, investigators, and budgets. Outpatient (OP) testing may be a solution although there are few reports on OP BCF testing variability. We compared variability metrics between OP and IP from a standardized mixed meal tolerance test (MMTT) and arginine stimulation test (AST) in two separate type 2 diabetes (T2DM) cohorts (OP, n = 20; IP n = 22) in test-retest design. MMTT variables included: insulin sensitivity (Si); beta cell responsivity (Φtot); and disposition index (DItot = Si* Φtot) following 470 kCal meal. AST variables included: acute insulin response to arginine (AIRarg) and during hyperglycemia (AIRargMAX).

Results

Baseline characteristics were well-matched. Between and within subject variance for each parameter across cohorts, and intraclass correlation coefficients (ICC-a measure of reproducibility) across parameters were generally comparable for OP to IP. Table summarizes the ICC results for each key parameter and cohort.

Test/Parameter	Outpatient (95% CI)	Inpatient (95% CI)
MMTT: Si	0.49(0,0.69)	0.28(0,0.60)
MMTT: Φtot	0.65(0.16,0.89)	0.81(0.44,0.93)
MMTT: DI	0.67(0,0.83)	0.36(0,0.69)
AST: AIR Arg	0.96(0.88,0.98)	0.84(0.59,0.94)
AST: AIR Arg Max	0.97(0.90,0.99)	0.95(0.86,0.97)
AST: ISR	0.93(0.77,0.97)	0.93(0.82,0.96)

In conclusion, the variability (reproducibility) of BCF measures from standardized MMTT and AST is comparable between OP and IP settings. These observations have significant implications for complexity and cost of metabolic studies.

Financial management of large, multi-center trials in a challenging funding milieu

BACKGROUND

Randomized clinical trials that have public health implications but no or low potential for commercial gain are predominantly funded by governmental (e.g., National Institutes of Health (NIH)) and not-for-profit organizations. Our objective was to develop an alternative clinical trial site funding model for judicious allocation of declining public research funds.

METHODS

In the Vitamin D and Type 2 Diabetes (D2d) study, an NIH-supported, large clinical trial testing the effect of vitamin D supplementation on incident diabetes in 2423 participants at high risk for diabetes, a hybrid financial management model for supporting collaborating clinical sites was developed and applied. The funding model employed two reimbursement components: Core (for study start-up and partial efforts throughout the study, ~40% of the total site budget), invoiced by sites, and Performance-Based Payments (for successful enrollment of participants and completion of follow-up visits, ~60% of the total site budget), automatically issued to the sites by the Coordinating Center based on actual recruitment and visits conducted. Underperforming sites transitioned to Performance-Based Payments only.

RESULTS

Recruitment occurred from October 2013 through December 2016, requiring one additional year than the 2-year projection. Median enrollment at each site was 88 participants (range 29-318; 20 to 205% of the site target). At the end of year 1, study-wide recruitment was at 12% of the target (vs. 50% projected) and 12% of the total grant award was invested. The model constantly evaluated sites' needs and re-allocated resources to meet the study enrollment goal. If D2d had issued cost reimbursement subaward agreements and sites invoiced for their entire budget, 83% of the award would have been spent for all study activities over the first 4 years of the trial compared to 65% of the award spent (US$26M) under the hybrid model used by D2d.

CONCLUSIONS

It is feasible to foster a hybrid financial management approach to steward limited available public funds for research in a dynamic and consistent way that does not compromise the trial's scientific integrity and ensures conservation of funds to complete recruitment and continue to follow up participants.

Prospective evaluation of insulin and incretin dynamics in obese adults with and without diabetes for 2 years after Roux-en-Y gastric bypass

AIMS/HYPOTHESIS

In this prospective case-control study we tested the hypothesis that, while long-term improvements in insulin sensitivity (S_I) accompanying weight loss after Roux-en-Y gastric bypass (RYGB) would be similar in obese individuals with and without type 2 diabetes mellitus, stimulated-islet-cell insulin responses would differ, increasing (recovering) in those with diabetes but decreasing in those without. We investigated whether these changes would occur in conjunction with favourable alterations in meal-related gut hormone secretion and insulin processing.

METHODS

Forty participants with type 2 diabetes and 22 participants without diabetes from the Longitudinal Assessment of Bariatric Surgery (LABS-2) study were enrolled in a separate, longitudinal cohort (LABS-3 Diabetes) to examine the mechanisms of postsurgical diabetes improvement. Study procedures included measures of S_I, islet secretory response and gastrointestinal hormone secretion after both intravenous glucose (frequently-sampled IVGTT [FSIVGTT]) and a mixed meal (MM) prior to and up to 24 months after RYGB.

RESULTS

Postoperatively, weight loss and S_I-_FSIVGTT improvement was similar in both groups, whereas the acute insulin response to glucose (AIRglu) decreased in the non-diabetic participants and increased in the participants with type 2 diabetes. The resulting disposition indices (DI_FSIVGTT) increased by three- to ninefold in both groups. In contrast, during the MM, total insulin responsiveness did not significantly change in either group despite durable increases of up to eightfold in postprandial glucagon-like peptide 1 levels, and S_I-MM and DI_MM increased only in the diabetes group. Peak postprandial glucagon levels increased in both groups.

CONCLUSIONS/INTERPRETATION

For up to 2 years following RYGB, obese participants without diabetes showed improvements in DI that approach population norms. Those with type 2 diabetes recovered islet-cell insulin secretion response yet continued to manifest abnormal insulin processing, with DI values that remained well below population norms. These data suggest that, rather than waiting for lifestyle or medical failure, RYGB is ideally considered before, or as soon as possible after, onset of type 2 diabetes.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00433810.

Standardized Mixed-Meal Tolerance and Arginine Stimulation Tests Provide Reproducible and Complementary Measures of β-Cell Function: Results From the Foundation for the National Institutes of Health Biomarkers Consortium Investigative Series

OBJECTIVE

Standardized, reproducible, and feasible quantification of β-cell function (BCF) is necessary for the evaluation of interventions to improve insulin secretion and important for comparison across studies. We therefore characterized the responses to, and reproducibility of, standardized methods of in vivo BCF across different glucose tolerance states.

RESEARCH DESIGN AND METHODS

Participants classified as having normal glucose tolerance (NGT; n = 23), prediabetes (PDM; n = 17), and type 2 diabetes mellitus (T2DM; n = 22) underwent two standardized mixed-meal tolerance tests (MMTT) and two standardized arginine stimulation tests (AST) in a test-retest paradigm and one frequently sampled intravenous glucose tolerance test (FSIGT).

RESULTS

From the MMTT, insulin secretion in T2DM was >86% lower compared with NGT or PDM (P < 0.001). Insulin sensitivity (Si) decreased from NGT to PDM (∼50%) to T2DM (93% lower [P < 0.001]). In the AST, insulin secretory response to arginine at basal glucose and during hyperglycemia was lower in T2DM compared with NGT and PDM (>58%; all P < 0.001). FSIGT showed decreases in both insulin secretion and Si across populations (P < 0.001), although Si did not differ significantly between PDM and T2DM populations. Reproducibility was generally good for the MMTT, with intraclass correlation coefficients (ICCs) ranging from ∼0.3 to ∼0.8 depending on population and variable. Reproducibility for the AST was very good, with ICC values >0.8 across all variables and populations.

CONCLUSIONS

Standardized MMTT and AST provide reproducible and complementary measures of BCF with characteristics favorable for longitudinal interventional trials use.

Type 2 Diabetes Remission Rates After Laparoscopic Gastric Bypass and Gastric Banding: Results of the Longitudinal Assessment of Bariatric Surgery Study

OBJECTIVE

The goals of this study were to determine baseline and postbariatric surgical characteristics associated with type 2 diabetes remission and if, after controlling for differences in weight loss, diabetes remission was greater after Roux-en-Y gastric bypass (RYGBP) than laparoscopic gastric banding (LAGB).

RESEARCH DESIGN AND METHODS

An observational cohort of obese participants was studied using generalized linear mixed models to examine the associations of bariatric surgery type and diabetes remission rates for up to 3 years. Of 2,458 obese participants enrolled, 1,868 (76%) had complete data to assess diabetes status at both baseline and at least one follow-up visit. Of these, 627 participants (34%) were classified with diabetes: 466 underwent RYGBP and 140 underwent LAGB.

RESULTS

After 3 years, 68.7% of RYGBP and 30.2% of LAGB participants were in diabetes remission. Baseline factors associated with diabetes remission included a lower weight for LAGB, greater fasting C-peptide, lower leptin-to-fat mass ratio for RYGBP, and a lower hemoglobin A1c without need for insulin for both procedures. After both procedures, greater postsurgical weight loss was associated with remission. However, even after controlling for differences in amount of weight lost, relative diabetes remission rates remained nearly twofold higher after RYGBP than LAGB.

CONCLUSIONS

Diabetes remission up to 3 years after RYGBP and LAGB was proportionally higher with increasing postsurgical weight loss. However, the nearly twofold greater weight loss-adjusted likelihood of diabetes remission in subjects undergoing RYGBP than LAGB suggests unique mechanisms contributing to improved glucose metabolism beyond weight loss after RYGBP.

Long-term outcomes of bariatric surgery: a National Institutes of Health symposium

IMPORTANCE

The clinical evidence base demonstrating bariatric surgery's health benefits is much larger than it was when the National Institutes of Health last held a consensus panel in 1991. Still, it remains unclear whether ongoing studies will address critical questions about long-term complication rates and the sustainability of weight loss and comorbidity control.

OBJECTIVE

To summarize findings from a multidisciplinary workshop convened in May 2013 by the National Institute of Diabetes and Digestive and Kidney Diseases and the National Heart, Lung, and Blood Institute. The workshop aimed to summarize the current state of knowledge of bariatric surgery, review research findings on the long-term outcomes of bariatric surgery, and establish priorities for future research directions.

EVIDENCE REVIEW

The evidence presented at the workshop was selected by the planning committee for both its quality and duration of follow-up. The data review emphasized randomized clinical trials and large observational studies with long-term follow-up, with or without a control group.

FINDINGS

Several small randomized clinical trials showed greater weight loss and type 2 diabetes mellitus remission compared with nonsurgical treatments within the first 2 years of follow-up after bariatric surgery. Large, long-term observational studies have shown durable (>5 years) weight loss, diabetes, and lipid improvements with bariatric surgery. Still unclear are predictors of outcomes, long-term complications, long-term survival, microvascular and macrovascular events, mental health outcomes, and costs. The studies needed to address these knowledge gaps would be expensive and logistically difficult to perform.

CONCLUSIONS AND RELEVANCE

High-quality evidence shows that bariatric surgical procedures result in greater weight loss than nonsurgical treatments and are more effective at inducing initial type 2 diabetes mellitus remission in obese patients. More information is needed about the long-term durability of comorbidity control and complications after bariatric procedures and this evidence will most likely come from carefully designed observational studies.

Rationale and design of the Vitamin D and Type 2 Diabetes (D2d) study: a diabetes prevention trial

OBJECTIVE

Observational studies suggest that vitamin D may lower the risk of type 2 diabetes. However, data from long-term trials are lacking. The Vitamin D and Type 2 Diabetes (D2d) study is a randomized clinical trial designed to examine whether a causal relationship exists between vitamin D supplementation and the development of diabetes in people at high risk for type 2 diabetes.

RESEARCH DESIGN AND METHODS

D2d was designed with support from a U34 planning grant from the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). The final protocol was approved by the D2d Research Group, the data and safety monitoring board, and NIDDK. Key eligibility criteria are age ≥30 years, BMI of 24 (22.5 for Asian Americans) to 42 kg/m(2), increased risk for diabetes (defined as meeting two of three glycemic criteria for prediabetes established by the American Diabetes Association [fasting glucose 100-125 mg/dL (5.5-6.9 mmol/L), 2-h postload glucose after 75-g glucose load 140-199 mg/dL (7.7-11.0 mmol/L), hemoglobin A₁c 5.7-6.4% (39-46 mmol/mol)]), and no hyperparathyroidism, nephrolithiasis, or hypercalcemia. D2d participants are randomized to once-daily vitamin D₃ (cholecalciferol 4,000 IU) or placebo and followed for an average of 3 years. The primary end point is time to incident diabetes as assessed by laboratory criteria during the study or by adjudication if diagnosed outside of D2d. Recruitment was initiated at the end of 2013.

CONCLUSIONS

D2d will test whether vitamin D supplementation is safe and effective at lowering the risk of progression to diabetes in people at high risk for type 2 diabetes.

Salicylate (salsalate) in patients with type 2 diabetes: a randomized trial

BACKGROUND

Short-duration studies show that salsalate improves glycemia in type 2 diabetes mellitus (T2DM).

OBJECTIVE

To assess 1-year efficacy and safety of salsalate in T2DM.

DESIGN

Placebo-controlled, parallel trial; computerized randomization and centralized allocation, with patients, providers, and researchers blinded to assignment. (ClinicalTrials.gov: NCT00799643).

SETTING

3 private practices and 18 academic centers in the United States.

PATIENTS

Persons aged 18 to 75 years with fasting glucose levels of 12.5 mmol/L or less (≤225 mg/dL) and hemoglobin A1c (HbA1c) levels of 7.0% to 9.5% who were treated for diabetes.

INTERVENTION

286 participants were randomly assigned (between January 2009 and July 2011) to 48 weeks of placebo (n = 140) or salsalate, 3.5 g/d (n = 146), in addition to current therapies, and 283 participants were analyzed (placebo, n = 137; salsalate, n = 146).

MEASUREMENTS

Change in hemoglobin A1c level (primary outcome) and safety and efficacy measures.

RESULTS

The mean HbA1c level over 48 weeks was 0.37% lower in the salsalate group than in the placebo group (95% CI, -0.53% to -0.21%; P < 0.001). Glycemia improved despite more reductions in concomitant diabetes medications in salsalate recipients than in placebo recipients. Lower circulating leukocyte, neutrophil, and lymphocyte counts show the anti-inflammatory effects of salsalate. Adiponectin and hematocrit levels increased more and fasting glucose, uric acid, and triglyceride levels decreased with salsalate, but weight and low-density lipoprotein cholesterol levels also increased. Urinary albumin levels increased but reversed on discontinuation; estimated glomerular filtration rates were unchanged.

LIMITATION

Trial duration and number of patients studied were insufficient to determine long-term risk-benefit of salsalate in T2DM.

CONCLUSION

Salsalate improves glycemia in patients with T2DM and decreases inflammatory mediators. Continued evaluation of mixed cardiorenal signals is warranted.

Effect of nutrition changes on foods selected by students in a middle school-based diabetes prevention intervention program: the HEALTHY experience

BACKGROUND

The HEALTHY primary prevention trial developed an integrated multicomponent intervention program to moderate risk factors for type 2 diabetes in middle schools. The nutrition component aimed to improve the quality of foods and beverages served to students. Changes in the School Breakfast Program (SBP), National School Lunch Program (NSLP), and à la carte venues are compared to the experience of control schools.

METHODS

The intervention was implemented in 21 middle schools from winter 2007 through spring 2009 (following a cohort of students from sixth through eighth grades); 21 schools acted as observed controls. The nutrition component targeted school food service environmental change. Data identifying foods and nutrients served (selected by students for consumption) were collected over a 20-day period at baseline and end of study. Analysis compared end of study values for intervention versus control schools.

RESULTS

Intervention schools more successfully limited dessert and snack food portion size in NSLP and à la carte and lowered fat content of foods served. Servings of high-fiber grain-based foods and/or legumes were improved in SBP but not NSLP. Intervention and control schools eliminated >1% fat milk and added-sugar beverages in SBP, but intervention schools were more successful in NSLP and à la carte.

CONCLUSION

The HEALTHY program demonstrated significant changes in the nutritional quality of foods and beverages served in the SBP, NSLP, and à la carte venues, as part of an effort to decrease childhood obesity and support beneficial effects in some secondary HEALTHY study outcomes.

Impact of the HEALTHY Study on Vending Machine Offerings in Middle Schools

PURPOSEOBJECTIVES

The purpose of this study is to report the impact of the three-year middle school-based HEALTHY study on intervention school vending machine offerings. There were two goals for the vending machines: serve only dessert/snack foods with 200 kilocalories or less per single serving package, and eliminate 100% fruit juice and beverages with added sugar.

METHODS

Six schools in each of seven cities (Houston, TX, San Antonio, TX, Irvine, CA, Portland, OR, Pittsburg, PA, Philadelphia, PA, and Chapel Hill, NC) were randomized into intervention (n=21 schools) or control (n=21 schools) groups, with three intervention and three control schools per city. All items in vending machine slots were tallied twice in the fall of 2006 for baseline data and twice at the end of the study, in 2009. The percentage of total slots for each food/beverage category was calculated and compared between intervention and control schools at the end of study, using the Pearson chi-square test statistic.

RESULTS

At baseline, 15 intervention and 15 control schools had beverage and/or snack vending machines, compared with 11 intervention and 11 control schools at the end of the study. At the end of study, all of the intervention schools with beverage vending machines, but only one out of the nine control schools, met the beverage goal. The snack goal was met by all of the intervention schools and only one of the four control schools with snack vending machines.

APPLICATIONS TO CHILD NUTRITION PROFESSIONALS

The HEALTHY study's vending machine beverage and snack goals were successfully achieved in intervention schools, reducing access to less healthy food items outside the school meals program. Although the effect of these changes on student diet, energy balance and growth is unknown, these results suggest that healthier options for snacks can successfully be offered in school vending machines.

Severe obesity and selected risk factors in a sixth grade multiracial cohort: the HEALTHY study

The purpose of this study was to document the prevalence of severe obesity and associated risk in the HEALTHY cohort. A total of 6,365 students were assessed at school-based screenings. Results showed that 6.9% of students were severely obese. Severe obesity was associated with elevated cardiometabolic risk and race/ethnicity. Severe obesity is common and requires preventive intervention.

The effects of salsalate on glycemic control in patients with type 2 diabetes: a randomized trial

BACKGROUND

Salsalate, a nonacetylated prodrug of salicylate, has been shown to decrease blood glucose concentration in small studies.

OBJECTIVE

To compare the efficacy and safety of salsalate at different doses in patients with type 2 diabetes.

DESIGN

Parallel randomized trial with computer-generated randomization and centralized allocation. Patients and investigators, including those assessing outcomes and performing analyses, were masked to group assignment. (ClinicalTrials.gov registration number: NCT00392678)

SETTING

3 private practices and 14 universities in the United States.

PATIENTS

Persons aged 18 to 75 years with fasting plasma glucose concentrations of 12.5 mmol/L or less (< or = 225 mg/dL) and hemoglobin A1c (HbA1c) levels of 7.0% to 9.5% treated by diet, exercise, and oral medication at stable doses for at least 8 weeks.

INTERVENTION

After a 4-week, single-masked run-in period, patients were randomly assigned to receive placebo or salsalate in dosages of 3.0, 3.5, or 4.0 g/d for 14 weeks (27 patients each) in addition to their current therapy.

MEASUREMENTS

Change in HbA1c was the primary outcome. Adverse effects and changes in measures of coronary risk and renal function were secondary outcomes.

RESULTS

Higher proportions of patients in the 3 salsalate treatment groups experienced decreases in HbA1c levels of 0.5% or more from baseline (P = 0.009). Mean HbA1c changes were -0.36% (P = 0.02) at 3.0 g/d, -0.34% (P = 0.02) at 3.5 g/d, and -0.49% (P = 0.001) at 4.0 g/d compared with placebo. Other markers of glycemic control also improved in the 3 salsalate groups, as did circulating triglyceride and adiponectin concentrations. Mild hypoglycemia was more common with salsalate; documented events occurred only in patients taking sulfonylureas. Urine albumin concentrations increased in all salsalate groups compared with placebo. The drug was otherwise well tolerated.

LIMITATION

The number of patients studied and the trial duration were insufficient to warrant recommending the use of salsalate for type 2 diabetes at this time.

CONCLUSION

Salsalate lowers HbA1c levels and improves other markers of glycemic control in patients with type 2 diabetes and may therefore provide a new avenue for treatment. Renal and cardiac safety of the drug require further evaluation.

PRIMARY FUNDING SOURCE

National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health.

The effects of salsalate on glycemic control in patients with type 2 diabetes: a randomized trial

BACKGROUND

Salsalate, a nonacetylated prodrug of salicylate, has been shown to decrease blood glucose concentration in small studies.

OBJECTIVE

To compare the efficacy and safety of salsalate at different doses in patients with type 2 diabetes.

DESIGN

Parallel randomized trial with computer-generated randomization and centralized allocation. Patients and investigators, including those assessing outcomes and performing analyses, were masked to group assignment. (ClinicalTrials.gov registration number: NCT00392678)

SETTING

3 private practices and 14 universities in the United States.

PATIENTS

Persons aged 18 to 75 years with fasting plasma glucose concentrations of 12.5 mmol/L or less (< or = 225 mg/dL) and hemoglobin A1c (HbA1c) levels of 7.0% to 9.5% treated by diet, exercise, and oral medication at stable doses for at least 8 weeks.

INTERVENTION

After a 4-week, single-masked run-in period, patients were randomly assigned to receive placebo or salsalate in dosages of 3.0, 3.5, or 4.0 g/d for 14 weeks (27 patients each) in addition to their current therapy.

MEASUREMENTS

Change in HbA1c was the primary outcome. Adverse effects and changes in measures of coronary risk and renal function were secondary outcomes.

RESULTS

Higher proportions of patients in the 3 salsalate treatment groups experienced decreases in HbA1c levels of 0.5% or more from baseline (P = 0.009). Mean HbA1c changes were -0.36% (P = 0.02) at 3.0 g/d, -0.34% (P = 0.02) at 3.5 g/d, and -0.49% (P = 0.001) at 4.0 g/d compared with placebo. Other markers of glycemic control also improved in the 3 salsalate groups, as did circulating triglyceride and adiponectin concentrations. Mild hypoglycemia was more common with salsalate; documented events occurred only in patients taking sulfonylureas. Urine albumin concentrations increased in all salsalate groups compared with placebo. The drug was otherwise well tolerated.

LIMITATION

The number of patients studied and the trial duration were insufficient to warrant recommending the use of salsalate for type 2 diabetes at this time.

CONCLUSION

Salsalate lowers HbA1c levels and improves other markers of glycemic control in patients with type 2 diabetes and may therefore provide a new avenue for treatment. Renal and cardiac safety of the drug require further evaluation.

PRIMARY FUNDING SOURCE

National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health.

Rationale, design and methods of the HEALTHY study nutrition intervention component

The HEALTHY study was a randomized, controlled, multicenter and middle school-based, multifaceted intervention designed to reduce risk factors for the development of type 2 diabetes. The study randomized 42 middle schools to intervention or control, and followed students from the sixth to the eighth grades. Here we describe the design of the HEALTHY nutrition intervention component that was developed to modify the total school food environment, defined to include the following: federal breakfast, lunch, after school snack and supper programs; a la carte venues, including snack bars and school stores; vending machines; fundraisers; and classroom parties and celebrations. Study staff implemented the intervention using core and toolbox strategies to achieve and maintain the following five intervention goals: (1) lower the average fat content of foods, (2) increase the availability and variety of fruits and vegetables, (3) limit the portion sizes and energy content of dessert and snack foods, (4) eliminate whole and 2% milk and all added sugar beverages, with the exception of low fat or nonfat flavored milk, and limit 100% fruit juice to breakfast in small portions and (5) increase the availability of higher fiber grain-based foods and legumes. Other nutrition intervention component elements were taste tests, cafeteria enhancements, cafeteria line messages and other messages about healthy eating, cafeteria learning laboratory (CLL) activities, twice-yearly training of food service staff, weekly meetings with food service managers, incentives for food service departments, and twice yearly local meetings and three national summits with district food service directors. Strengths of the intervention design were the integration of nutrition with the other HEALTHY intervention components (physical education, behavior change and communications), and the collaboration and rapport between the nutrition intervention study staff members and food service personnel at both school and district levels.

Perioperative safety in the longitudinal assessment of bariatric surgery

BACKGROUND

To improve decision making in the treatment of extreme obesity, the risks of bariatric surgical procedures require further characterization.

METHODS

We performed a prospective, multicenter, observational study of 30-day outcomes in consecutive patients undergoing bariatric surgical procedures at 10 clinical sites in the United States from 2005 through 2007. A composite end point of 30-day major adverse outcomes (including death; venous thromboembolism; percutaneous, endoscopic, or operative reintervention; and failure to be discharged from the hospital) was evaluated among patients undergoing first-time bariatric surgery.

RESULTS

There were 4776 patients who had a first-time bariatric procedure (mean age, 44.5 years; 21.1% men; 10.9% nonwhite; median body-mass index [the weight in kilograms divided by the square of the height in meters], 46.5). More than half had at least two coexisting conditions. A Roux-en-Y gastric bypass was performed in 3412 patients (with 87.2% of the procedures performed laparoscopically), and laparoscopic adjustable gastric banding was performed in 1198 patients; 166 patients underwent other procedures and were not included in the analysis. The 30-day rate of death among patients who underwent a Roux-en-Y gastric bypass or laparoscopic adjustable gastric banding was 0.3%; a total of 4.3% of patients had at least one major adverse outcome. A history of deep-vein thrombosis or pulmonary embolus, a diagnosis of obstructive sleep apnea, and impaired functional status were each independently associated with an increased risk of the composite end point. Extreme values of body-mass index were significantly associated with an increased risk of the composite end point, whereas age, sex, race, ethnic group, and other coexisting conditions were not.

CONCLUSIONS

The overall risk of death and other adverse outcomes after bariatric surgery was low and varied considerably according to patient characteristics. In helping patients make appropriate choices, short-term safety should be considered in conjunction with both the long-term effects of bariatric surgery and the risks associated with being extremely obese. (ClinicalTrials.gov number, NCT00433810.)

Effects of 7 days of exercise training on insulin sensitivity and responsiveness in type 2 diabetes mellitus

The objectives of this study were to determine whether 1) the improvement in insulin action induced by short-term exercise training in patients with type 2 diabetes is due to an improvement in insulin sensitivity, an improvement in insulin responsiveness, or a combination of improved insulin sensitivity and responsiveness and 2) short-term exercise training results in improved suppression of hepatic glucose production by insulin. Fourteen obese patients with type 2 diabetes, age 64 +/- 2 yr, underwent a two-stage hyperinsulinemic euglycemic clamp procedure, first stage 40 mU.m(-2).min(-1) insulin infusion, second stage 1,000 mU.m(-2).min(-1) insulin infusion, together with a [3-(3)H]glucose infusion, before and after 7 days of exercise. The training consisted of 30 min of cycling and 30 min of treadmill walking at approximately 70% of maximal aerobic capacity daily for 7 days. The exercise program resulted in improvements in insulin action in the absence of weight loss. Glucose disposal rates during the euglycemic clamp were significantly increased at both hyperinsulinemic stages after training (40 mU: 1.84 +/- 0.32 to 2.67 +/- 0.37 mg.kg(-1).min(-1), P < 0.0001; 1,000 mU: 7.57 +/- 0.61 to 8.84 +/- 0.56 mg.kg(-1).min(-1), P = 0.008). Hepatic glucose production, both in the basal state (3.17 +/- 0.43 vs. 2.54 +/- 0.26 mg.kg(-1).min(-1), P = 0.05) and during the 40-mU clamp stage (1.15 +/- 0.41 vs. 0.46 +/- 0.20 mg.kg(-1).min(-1), P = 0.03), was significantly reduced after training. One week of vigorous exercise training can induce significant improvements in insulin action in type 2 diabetes. These improvements include increased peripheral insulin sensitivity and responsiveness as well as enhanced suppression of hepatic glucose production.

Challenges in the Discovery and Development of New Agents for the Treatment of Obesity

New pharmacologic agents are being sought to help manage the epidemic of obesity and its consequences. Understanding the challenges of the history of obesity drugs is wise before investing in new obesity agents. Expectations of patients, physicians, and drug company executives are not consistent with characteristics of current agents or most potential new ones. Owing to the complex biology underlying body weight regulation, combinations of agents may be necessary to improve weight loss efficacy.

Relationship between glucose tolerance and glucose-stimulated insulin response in 65-year-olds

BACKGROUND

Decreased insulin secretion may contribute to the deterioration of glucose tolerance associated with aging.

METHODS

We studied the insulin response to a 3-hour hyperglycemic clamp (10 mM) of 19 young (24 +/- 1 y) subjects with normal glucose tolerance and 60 older (65 +/- 1 y) subjects with various levels of glucose tolerance.

RESULTS

The noninsulin dependent diabetic (NIDDM) group had a diminished first phase immunoreactive (IR)-insulin response compared to young and nondiabetic older groups (p < .05). The older groups had a lower rate of change in IR insulin concentration during the third hour of hyperglycemia compared to the young group (p < .05). This was not, however, a universal finding, because a decreased third hour response was not seen in a subgroup of older subjects whose glucose tolerance was similar to that of the young group. Another subgroup of older subjects with a decrease in glucose tolerance mild enough to be considered normal by the National Diabetes Group Criteria tended to have both an increase in the early insulin response and a decrease in the third hour response. More severe decreases in glucose tolerance were associated with blunting of the early response.

CONCLUSION

Aberrations in early and late phase glucose-stimulated insulin responses appear to be present in older subjects with even mildly decreased glucose tolerance. Some individuals, however, show no evidence of deterioration of glucose tolerance or insulin response to glucose with aging, at least up to age 70 years.

Insulin resistance in aging is related to abdominal obesity

Studies have shown that insulin resistance increases with age, independent of changes in total adiposity. However, there is growing evidence that the development of insulin resistance may be more closely related to abdominal adiposity. To evaluate the independent effects of aging and regional and total adiposity on insulin resistance, we performed hyperinsulinemic euglycemic clamps on 17 young (21-33 yr) and 67 older (60-72 yr) men and women. We assessed FFM and total and regional adiposity by hydrodensitometry and anthropometry. Insulin-stimulated GDRs at a plasma insulin concentration of approximately 450 pM averaged 45.6 +/- 3.3 mumol.kg FFM-1 x min-1 (mean +/- SE) in the young subjects, 45.6 +/- 10.0 mumol.kg FFM-1 x min-1 in 24 older subjects who were insulin sensitive, and 23.9 +/- 11.7 mumol.kg FFM-1 x min-1 in 43 older subjects who were insulin resistant. Few significant differences were apparent in skin-fold and circumference measurements between young and insulin-sensitive older subjects, but measurements at most central body sites were significantly larger in the insulin-resistant older subjects. Waist girth accounted for > 40% of the variance in insulin action, whereas age explained only 10-20% of the total variance and < 2% of the variance when the effects of waist circumference were statistically controlled. These results suggest that insulin resistance is more closely associated with abdominal adiposity than with age.

Effects of treadmill exercise to exhaustion on the insulin response to hyperglycemia in untrained men

The effects of a single bout of exercise to exhaustion on pancreatic insulin secretion were determined in seven untrained men by use of a 3-h hyperglycemic clamp with plasma glucose maintained at 180 mg/100 ml. Clamps were performed either 12 h after an intermittent treadmill run at approximately 77% maximum O2 consumption or without prior exercise. Arterialized blood samples for glucose, insulin, and C-peptide determination were obtained from a heated hand vein. The peak insulin response during the early phase (0-10 min) of the postexercise clamp was higher (81 +/- 8 vs. 59 +/- 9 microU/ml; P less than 0.05) than in the nonexercise clamp. Incremental areas under the insulin (376 +/- 33 vs. 245 +/- 51 microU.ml-1.min) and C-peptide (17 +/- 2 vs. 12 +/- 1 ng.ml-1.min) curves were also greater (P less than 0.05) during the early phase of the postexercise clamp. No differences were observed in either insulin concentrations or whole body glucose disposal during the late phase (15-180 min). Area under the C-peptide curve was greater during the late phase of the postexercise clamp (650 +/- 53 vs. 536 +/- 76 ng.ml-1.min, P less than 0.05). The exercise bout induced muscle soreness and caused an elevation in plasma creatine kinase activity (142 +/- 32 vs. 305 +/- 31 IU/l; P less than 0.05) before the postexercise clamp. We conclude that in untrained men a bout of running to exhaustion increased pancreatic beta-cell insulin secretion during the early phase of the hyperglycemic clamp. Increased insulin secretion during the late phase of the clamp appeared to be compensated by increased insulin clearance.

The effect of exercise on food intake in men and women

To study the effect of acute exercise on caloric intake in normal-weight young people, food intake was monitored in 10 men and 10 women during consecutive 5-d periods, one with and one without exercise. Food intake during the exercise period was compared with that during the control period. Caloric intake during the control period was 2467 +/- 165 kcal/d (means +/- SEM) for men and 1831 +/- 103 kcal/d for women. During the exercise period the men increased their caloric intake to 2658 +/- 188 kcal/d and the women's caloric intake remained unchanged, 1830 +/- 91 kcal/d. Caloric intake was not affected by sequence of treatment or duration of protocol. Men responded to 5 d of acute exercise with increased caloric intake (208 +/- 64 kcal/d), which was insufficient to compensate for the caloric cost of exercise (596 kcal/d above resting metabolic rate). Women did not change their caloric intake despite expending 382 kcals/d during exercise. Consequently, both normal-weight men and women were in negative caloric balance during the exercise period.

Insulin secretory capacity in endurance-trained and untrained young men

Insulin secretion in response to glucose stimulation is reduced in endurance-trained humans. In this study, a modified hyperglycemic clamp, with a superimposed arginine infusion and fat meal, was performed on eight endurance-trained and nine untrained men to determine whether insulin secretory capacity is reduced by exercise training. Raising the plasma glucose concentration to approximately 450 mg/dl resulted in a plasma insulin response in the trained men that was approximately 64% lower than that of the untrained (peak values: 54 +/- 8 vs. 149 +/- 35 microU/ml; P less than 0.001). When a primed continuous infusion of arginine was superimposed on the hyperglycemia, the plasma insulin response was also markedly lower (66%) in the trained subjects, reaching peak values of 333 +/- 68 and 974 +/- 188 microU/ml for trained and untrained subjects, respectively (P less than 0.005). When insulin secretion was further stimulated during the arginine-infused hyperglycemia by the ingestion of a high-fat meal, peak insulin concentrations averaged 989 +/- 205 microU/ml in the trained compared with 2,232 +/- 455 microU/ml in the untrained subjects (P less than 0.01). The response of gastric inhibitory polypeptide (GIP) to the fat meal was delayed and blunted, suggesting that some enteric factor(s) other than GIP mediated the insulinotropic effect of the fat meal. The reduced plasma insulin response in trained people to the stimuli investigated suggests that regular exercise produces either several adaptations within the beta-cell or a single alteration of the beta-cell that results in an attenuation of the insulin secretory response to glucose, arginine, and fat ingestion.

Epinephrine's effect on metabolic rate is independent of changes in plasma insulin or glucagon

Epinephrine's effect to increase metabolic rate is accompanied by changes in the plasma concentrations of insulin, glucagon, and metabolic substrates. Because both glucagon and insulin have been reported to affect thermogenesis, these hormones might contribute to or modify the thermogenic response to epinephrine. To determine if the epinephrine-induced increase in metabolic rate is secondary to changes in glucagon or insulin or to changes in the fuels modulated by these hormones, metabolic rate was measured by indirect calorimetry in five normal weight post-absorptive young men on three occasions: study A, an intravenous epinephrine infusion alone; study B, a 4-h "islet clamp" consisting of somatostatin infusion with basal insulin and glucagon replacement; and study C, an intravenous epinephrine infusion combined with the islet clamp. A 1-h base-line period preceded 2 h of epinephrine infusion. During the 4-h islet clamp (study B), metabolic rate and plasma concentrations of epinephrine, insulin, glucagon, and glucose remained unchanged. During the infusion of epinephrine alone (study A), metabolic rate and concentrations of glucagon, free fatty acids, and C-peptide increased as expected. Also as expected, the glycemic response to epinephrine infusion was much larger when insulin and glucagon levels were fixed with the islet clamp (study C). In contrast, the metabolic rate and the free fatty acid concentration responded similarly to epinephrine infusion when insulin and glucagon were fixed (study C) and when they were changing (study A). We conclude that epinephrine increases metabolic rate independently of physiological changes in plasma glucagon or insulin or the circulating fuels they modulate.

Measurement of fat distribution by magnetic resonance imaging

Because of the important role of intra-abdominal fat in predicting increased risk for diabetes, hypertension, and heart disease, methods to quantify intra-abdominal fat are needed. Computed tomography defines quantity of intra-abdominal fat but is associated with significant radiation risk. We explored using magnetic resonance imaging (MRI) to measure amount and distribution of intra-abdominal fat. Because MRI has no known risk, the same subject can be studied repeatedly. Six subjects with percent body fat ranging from 14% to 44% had MRI scans of the chest, abdomen, and thigh on two separate occasions. Total abdominal fat and subcutaneous abdominal fat correlated with percent total body fat as determined from hydrostatic weighing (r = .99, P less than .001). Intra-abdominal fat correlated with the ratio of widest abdominal to widest hip circumference (r = .85, P less than .05). Reproducibility of the MRI measurements of fat was less than 3% for total body areas, less than 5% for subcutaneous fat areas, and less than 10% for internal fat areas. Reproducibility was better in individuals with higher percent total body fat. We conclude that MRI can reliably measure fat areas with no radiation risk to the patient.

Effects of lack of exercise on insulin secretion and action in trained subjects

We employed the hyperglycemic clamp technique to investigate the effects of short-term inactivity on insulin secretion in nine (8 men, 1 woman) well-trained subjects. A 3-h hyperglycemic clamp (plasma glucose approximately 180 mg/100 ml) was performed approximately 16 h after a usual training bout and again 14 days after stopping exercise training. There was no significant change in body composition during this short period of inactivity. The mean plasma insulin response to an identical glycemic stimulus was 67% higher after 14 days without exercise (45 +/- 7 after vs. 27 +/- 4 microU/ml before stopping exercise training). Marked increases in the early (0-10 min, 150 +/- 28 vs. 101 +/- 15 microU.ml-1.min) and late (10-180 min, 6,051 +/- 1,257 vs. 3,521 +/- 749 microU.ml-1.min) incremental insulin areas were observed as a result of the physical inactivity. Incremental areas for C-peptide were also elevated significantly in the inactive state for early (12 +/- 2.0 vs. 7 +/- 1 ng.ml-1.min) and late (567 +/- 90 vs. 467 +/- 85 ng.ml-1.min) phases. Urinary excretion of C-peptide increased from 12.1 +/- 1.5 ng/240 min in the exercising state to 21.8 +/- 3.6 ng/240 min in the inactive state. Rates of whole body glucose disposal were not different between exercising and inactive states, indicating a large increase in resistance to the action of insulin. These findings indicate that the decreased insulin secretory response to a glucose stimulus in people who exercise regularly is a relatively short-term effect of exercise.

Effects of exercise and lack of exercise on insulin sensitivity and responsiveness

Insulin action is enhanced in people who exercise regularly and vigorously. In the present study, the hyperinsulinemic, euglycemic clamp procedure was used to determine whether this enhanced insulin action is due to an increased sensitivity and/or an increased responsiveness to insulin. To avoid the variability that exists between individuals and complicates cross-sectional studies, the same subjects were studied in the trained exercising state and again after 10 days of physical inactivity. When the plasma insulin concentration was maintained at approximately 78 microU.ml-1 (a submaximal level), glucose disposal rate averaged 8.7 +/- 0.5 mg.kg-1.min-1 before and 6.7 +/- 0.6 mg.kg-1.min-1 after 10 days of activity (P less than 0.001). When the plasma insulin concentration was maintained at approximately 2,000 microU.ml-1 (a maximally effective concentration), the rate of glucose disposal was not significantly different before (15.3 +/- 0.5 mg.kg-1.min-1) compared with after (14.5 +/- 0.4 mg.kg-1.min-1) 10 days without exercise. These results provide evidence that the reversal of enhanced insulin action that occurs within a few days when exercise-trained individuals stop exercising is due to a decrease in sensitivity to insulin, not to a decrease in insulin responsiveness.

Insulin action and secretion in endurance-trained and untrained humans

To evaluate insulin sensitivity and responsiveness, a two-stage hyperinsulinemic euglycemic clamp procedure (insulin infusions of 40 and 400 mU.m-2.min-1) was performed on 11 endurance-trained and 11 untrained volunteers. A 3-h hyperglycemic clamp procedure (plasma glucose approximately 180 mg/dl) was used to study the insulin response to a fixed glycemic stimulus in 15 trained and 12 untrained subjects. During the 40-mU.m-2.min-1 insulin infusion, the glucose disposal rate was 10.2 +/- 0.5 mg.kg fat-free mass (FFM)-1.min-1 in the trained group compared with 8.0 +/- 0.6 mg.kg FFM-1.min-1 in the untrained group (P less than 0.01). In contrast, there was no significant difference in maximally stimulated glucose disposal: 17.7 +/- 0.6 in the trained vs. 16.7 +/- 0.7 mg.kg FFM-1.min-1 in the untrained group. During the hyperglycemic clamp procedure, the incremental area for plasma insulin was lower in the trained subjects for both early (0-10 min: 140 +/- 18 vs. 223 +/- 23 microU.ml-1.min; P less than 0.005) and late (10-180 min: 4,582 +/- 689 vs. 8,895 +/- 1,316 microU.ml-1.min; P less than 0.005) insulin secretory phases. These data demonstrate that 1) the improved insulin action in healthy trained subjects is due to increased sensitivity to insulin, with no change in responsiveness to insulin, and 2) trained subjects have a smaller plasma insulin response to an identical glucose stimulus than untrained individuals.

Physiological increments in epinephrine stimulate metabolic rate in humans

Markedly elevated plasma epinephrine is known to increase metabolic rate (MR), but such levels of epinephrine are encountered infrequently in normal free-living subjects. We studied whether epinephrine levels common in usual daily activities can affect MR and thus possibly regulate caloric expenditure. To aid definition of a MR threshold, we first measured the hourly and daily variation in MR within individuals by measuring the MR of four individuals by indirect calorimetry for 6 h on six separate occasions without any intervention. We found that hour-to-hour variation (2.0 +/- 0.9%) and the day-to-day variation (2.7 +/- 0.9%) were low, thus allowing confident detection of small increments in metabolic rate during epinephrine infusion. To define a threshold for epinephrine's effect to increase MR, we studied five normal-weight postabsorptive young men on four separate occasions. During the 1st h of each 5-h study period, saline was infused intravenously. Then, during the subsequent 4 h, subjects received intravenous infusion of saline or epinephrine at 0.1, 0.5, and 1.0 microgram/min (randomized). A significant increase in MR (3.6 +/- 1.0% SE) was measured with the lowest epinephrine infusion rate (venous plasma concentration, 94 +/- 32 pg/ml). The increases in MR correlated (r = 0.85, P less than 0.001) with increases in plasma epinephrine. The threshold concentration (upper 95% confidence limit) of epinephrine to affect MR was 90 pg/ml, a concentration frequently occurring in daily life. Thus epinephrine may play an important role in weight maintenance by affecting energy expenditure.

Leucine metabolism in type II diabetes mellitus

Severe muscle wasting is a well-recognized characteristic of untreated insulin-deficient diabetes mellitus, a condition in which leucine turnover and oxidation are accelerated. To ascertain whether a similar circumstance exists in type II diabetes when insulin is present but with reduced efficacy, we investigated leucine turnover and oxidation in five obese type II diabetic women by tracer infusion of L-[1-13C,15N]leucine in the postabsorptive state both before and after intensive insulin therapy. With conventional treatment, the type II diabetic women received 61 +/- 33 (SD) U/day of insulin, and their fasting plasma glucose averaged 194 +/- 41 (SD) mg/dl. Leucine carbon flux (QC), nitrogen flux (QN), and oxidation (C) averaged 6.4 +/- 1.2, 15.6 +/- 4.6, and 1.4 +/- 0.3 mmol/h, respectively. These values were not different from the respective values of 6.6 +/- 1.3, 17.0 +/- 8.3, and 1.0 +/- 0.2 mmol/h in matched obese nondiabetic controls, suggesting that leucine metabolism is not altered in insulin-treated type II diabetics. After a week of intensive insulin therapy in which the same diabetic subjects received 94 +/- 36 U/day of insulin, postabsorptive plasma glucose declined to 117 +/- 26 mg/dl. Leucine QC (6.2 +/- 1.0), QN (14.8 +/- 3.7), and C (1.5 +/- 0.5 mmol/h) were unaltered by the increased insulin therapy. Thus, obese type II diabetics had normal leucine kinetics but were hyperglycemic while receiving conventional insulin therapy. Additional intensive insulin therapy in these diabetic subjects improved plasma glucose but did not alter leucine kinetics.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of valine metabolism in man: a stable isotope study

Valine and leucine kinetics were studied in four young healthy men in the postabsorptive state with a 4-h primed infusion of either L-[1-13C,15N] valine or L-[1-13C,15N]-leucine. For 1 wk before each infusion study each subject consumed a diet that provided an adequate amount of energy and 1.6 kg/day of protein. During infusion of tracer, plasma valine or leucine, and expired 13CO2 reached isotopic steady state by 2 h. The valine and leucine carbon fluxes (mean +/- SE) were 80.3 +/- 1.2 and 86.6 +/- 2.0 mumol kg-1h-1, respectively, consistent with the lesser content of valine compared with leucine in body protein. Valine and leucine oxidation rates were 11.8 +/- 0.6 and 15.9 +/- 1.1 mumol kg-1h-1, respectively. From these values and values for valine and leucine nitrogen flux, the rates of valine and leucine transamination were calculated. Valine and leucine deamination were 84.0 +/- 3.5 and 103.0 +/- 6.5 mumol kg-1h-1, and values for reamination were 72.2 +/- 3.3 and 87.1 +/- 7.5 mumol kg-1h-1, respectively. Thus, the patterns of valine and leucine catabolism are similar. However, when the plasma substrate levels are used to estimate transamination rate constants, we estimate that the transamination equilibrium favors leucine transamination over valine by 5-fold.

Usefulness of screening chest roentgenograms in preoperative patients

We proposed that clinical criteria could define a group of patients very unlikely to have abnormal preoperative chest roentgenograms. Nine hundred five surgical admissions were screened for the presence of clinical factors we thought would make those patients more likely to have abnormal preoperative chest roentgenograms. Of these, 368 had no risk factors. One patient (0.3%) of the 368 had an abnormal x-ray film, which did not affect the surgery. No material abnormalities were found in the remainder of the group without risk factors. Five hundred four patients had identifiable risk factors. Of these, 114 (22%) were found to have serious abnormalities on preoperative chest roentgenogram.