Effects of single bout resistance exercise on glucose levels, insulin action, and cardiovascular risk in type 2 diabetes: A narrative review

AIMS

Previous studies have reported beneficial effects of chronic resistance exercise in the prevention and treatment of type 2 diabetes. To clarify potential modulators of acute responses to resistance exercise, we reviewed the literature to determine the effects of a single bout of resistance exercise on cardiometabolic risk factors in type 2 diabetes.

METHODS

Pubmed and Embase were searched for studies investigating the effects of single bouts of resistance exercise on glucose and insulin levels, and cardiovascular disease risk in people with diabetes. Fourteen reports were identified and reviewed to formulate evidence-based resistance exercise prescription recommendations.

RESULTS

Glucose and insulin levels appear to decrease with resistance exercise with effects lasting up to 24 and 18 h, respectively. Bouts of resistance exercise may outperform aerobic exercise in reducing ambulatory blood pressure, with effects lasting up to 24 h. Moreover, resistance exercise after rather than before a meal may be more effective in reducing glucose, insulin, and triacylglycerol levels. However, reducing injectable insulin dosage prior to resistance exercise may blunt its favorable effects on glucose levels.

CONCLUSIONS

This review suggests that a single bout of resistance exercise may be effective for acutely improving cardiometabolic markers in people with diabetes.

GLP-1 and insulin regulation of skeletal and cardiac muscle microvascular perfusion in type 2 diabetes

Muscle microvasculature critically regulates skeletal and cardiac muscle health and function. It provides endothelial surface area for substrate exchange between the plasma compartment and the muscle interstitium. Insulin fine-tunes muscle microvascular perfusion to regulate its own action in muscle and oxygen and nutrient supplies to muscle. Specifically, insulin increases muscle microvascular perfusion, which results in increased delivery of insulin to the capillaries that bathe the muscle cells and then facilitate its own transendothelial transport to reach the muscle interstitium. In type 2 diabetes, muscle microvascular responses to insulin are blunted and there is capillary rarefaction. Both loss of capillary density and decreased insulin-mediated capillary recruitment contribute to a decreased endothelial surface area available for substrate exchange. Vasculature expresses abundant glucagon-like peptide 1 (GLP-1) receptors. GLP-1, in addition to its well-characterized glycemic actions, improves endothelial function, increases muscle microvascular perfusion, and stimulates angiogenesis. Importantly, these actions are preserved in the insulin resistant states. Thus, treatment of insulin resistant patients with GLP-1 receptor agonists may improve skeletal and cardiac muscle microvascular perfusion and increase muscle capillarization, leading to improved delivery of oxygen, nutrients, and hormones such as insulin to the myocytes. These actions of GLP-1 impact skeletal and cardiac muscle function and systems biology such as functional exercise capacity. Preclinical studies and clinical trials involving the use of GLP-1 receptor agonists have shown salutary cardiovascular effects and improved cardiovascular outcomes in type 2 diabetes mellitus. Future studies should further examine the different roles of GLP-1 in cardiac as well as skeletal muscle function.

Mechanistic Causes of Reduced Cardiorespiratory Fitness in Type 2 Diabetes

Type 2 diabetes (T2D) has been rising in prevalence in the United States and worldwide over the past few decades and contributes to significant morbidity and premature mortality, primarily due to cardiovascular disease (CVD). Cardiorespiratory fitness (CRF) is a modifiable cardiovascular (CV) risk factor in the general population and in people with T2D. Young people and adults with T2D have reduced CRF when compared with their peers without T2D who are similarly active and of similar body mass index. Furthermore, the impairment in CRF conferred by T2D is greater in women than in men. Various factors may contribute to this abnormality in people with T2D, including insulin resistance and mitochondrial, vascular, and cardiac dysfunction. As proof of concept that understanding the mediators of impaired CRF in T2D can inform intervention, we previously demonstrated that an insulin sensitizer improved CRF in adults with T2D. This review focuses on how contributing factors influence CRF and why they may be compromised in T2D. Functional exercise capacity is a measure of interrelated systems biology; as such, the contribution of derangement in each of these factors to T2D-mediated impairment in CRF is complex and varied. Therefore, successful approaches to improve CRF in T2D should be multifaceted and individually designed. The current status of this research and future directions are outlined.

Educating the Scientific Workforce on Sex and Gender Considerations in Research: A National Scan of the Literature and Building Interdisciplinary Research Careers in Women's Health Programs

Background: This study was a national scan of education resources on integrating sex and gender considerations into research. The purpose was to assess capacity for educating researchers and to identify gaps, with implications for implementation of guidelines or mandates to consider sex and gender differences in research. Information sources were U.S. training programs in women's health and sex/gender difference research, Building Interdisciplinary Research Careers in Women's Health (BIRCWH), and published peer-reviewed biomedical literature. Materials and Methods: This descriptive study used multiple methods: a national survey and a comprehensive literature review. BIRCWH leaders responded to a survey regarding education on sex/gender difference research for BIRCWH scholars (response rate 100%, 20 of 20). A comprehensive literature review was conducted for 1993-2018. Results: Nearly half (45%) of BIRCWH institutions offered education on integrating sex or gender differences in clinical translational research; of those, roughly half (54%) offered in-person training and one-third (31%) offered content within existing for-credit courses. Respondents preferred online training (84%) to in-person offerings or reference materials (47% and 42% respectively). Published indexed literature on sex or gender differences has quadrupled since 1993, although growth in these publications remained flat in the most recent six years. Conclusions: Published resources to educate researchers on integrating sex and gender differences into medical research have increased, and BIRCWH programs connect scholars to national resources. Educational gaps remain due to limited access to curricula on applied research approaches, design, and methods for sex/gender difference research. BIRCWH programs desire curricula that are easily accessible online and asynchronously; sanctioned and supported by national thought leaders; linked to required training such as rigor and reproducibility; foster collaboration; and offer practical applications. Evidence-based, high-quality educational curricula and a dissemination plan are needed to enhance the adoption and integration of sex and gender into scientific endeavors.

Sex Differences Across the Lifespan: A Focus on Cardiometabolism

Women's health and sex differences research remain understudied. In 2016, to address the topic of sex differences, the Center for Women' s Health Research (CWHR) at the University of Colorado (cwhr@ucdenver.edu) held its inaugural National Conference, "Sex Differences Across the Lifespan: A Focus on Metabolism" and published a report summarizing the presentations. Two years later, in 2018, CWHR organized the 2nd National Conference. The research presentations and discussions from the 2018 conference also addressed sex differences across the lifespan with a focus on cardiometabolism and expanded the focus by including circadian physiology and effects of sleep on cardiometabolic health. Over 100 participants, including basic scientists, clinicians, policymakers, advocacy group leaders, and federal agency leadership participated. The meeting proceedings reveal that although exciting advances in the area of sex differences have taken place, significant questions and gaps remain about women's health and sex differences in critical areas of health. Identifying these gaps and the subsequent research that will result may lead to important breakthroughs.

Abnormal Exercise Test or CVD History on Weight Loss or Fitness: the Look AHEAD Trial

PURPOSE

Obesity and type 2 diabetes are associated with an increased risk of cardiovascular disease (CVD) and the combination of weight loss and increased physical exercise are commonly recommended to reduce CVD. This study examined whether people with obesity and type 2 diabetes with an abnormal graded exercise tolerance test (GXT) or a history of CVD would have less success in achieving weight loss and improved fitness, compared to adults without these conditions.

METHODS

The Look AHEAD Study examined whether an intensive lifestyle intervention (ILI) compared with diabetes support and education (DSE) reduced cardiovascular events in adults with overweight/obesity and type 2 diabetes. Participants underwent a baseline maximal GXT and provided medical history data. Weight loss and fitness change were examined in 5011 participants over four years in those with or without an abnormal baseline GXT and/or history of CVD.

RESULTS

After four years, weight loss in both ILI and DSE were significantly greater in those without a prior history of CVD than in those with a CVD history (6.69% vs 5.98%, p=0.02, in ILI and 0.73 vs -.07% (weight gain), p=0.01, in DSE). Likewise, those without a prior history of CVD experienced greater improvements in fitness in both ILI and DSE relative to those with a history of CVD. Having an abnormal GXT at baseline did not affect weight loss or fitness.

CONCLUSIONS

A history of CVD at baseline modestly lessened weight loss and fitness changes at 4 years, whereas having any abnormality on the baseline GXT did not affect these outcomes. Thus, weight loss and improved fitness are achievable in adults with a history of CVD or ECG abnormalities.

The Most Valuable Resource Is Time: Insights From a Novel National Program to Improve Retention of Physician-Scientists With Caregiving Responsibilities

PURPOSE

To enhance understanding of challenges related to work-life integration in academic medicine and to inform the ongoing implementation of an existing program and the development of other interventions to promote success of physician-scientists.

METHOD

This study is part of a prospective analysis of the effects of the Fund to Retain Clinical Scientists (FRCS), a national program launched by the Doris Duke Charitable Foundation at 10 U.S. institutions, which provides financial support to physician-scientists facing caregiving challenges. In early 2018, 28 of 33 program awardees participated in semistructured interviews. Questions were about challenges faced by physician-scientists as caregivers and their early perceptions of the FRCS. Multiple analysts reviewed deidentified transcripts, iteratively revised the coding scheme, and interpreted the data using qualitative thematic analysis.

RESULTS

Participants' rich descriptions illuminated 5 interconnected themes: (1) Time is a critical and limited resource, (2) timing is key, (3) limited time resources and timing conflicts may have a particularly adverse effect on women's careers, (4) flexible funds enable reclamation and repurposing of time resources, and (5) FRCS leaders should be cognizant of time and timing conflicts when developing program-related offerings.

CONCLUSIONS

Programs such as the FRCS are instrumental in supporting individuals to delegate time-consuming tasks and to control how they spend their valuable time. Qualitative analysis suggests that access to and command of valuable time resources are crucial to career advancement, research productivity, and work-life flexibility, especially during critical time points along the physician-scientist trajectory.

Sex differences in the burden of type 2 diabetes and cardiovascular risk across the life course

By 2017 estimates, diabetes mellitus affects 425 million people globally; approximately 90-95% of these have type 2 diabetes. This narrative review highlights two domains of sex differences related to the burden of type 2 diabetes across the life span: sex differences in the prevalence and incidence of type 2 diabetes, and sex differences in the cardiovascular burden conferred by type 2 diabetes. In the presence of type 2 diabetes, the difference in the absolute rates of cardiovascular disease (CVD) between men and women lessens, albeit remaining higher in men. Large-scale observational studies suggest that type 2 diabetes confers 25-50% greater excess risk of incident CVD in women compared with men. Physiological and behavioural mechanisms that may underpin both the observed sex differences in the prevalence of type 2 diabetes and the associated cardiovascular burden are discussed in this review. Gender differences in social behavioural norms and disparities in provider-level treatment patterns are also highlighted, but not described in detail. We conclude by discussing research gaps in this area that are worthy of further investigation.

Implementation of Supervised Exercise Therapy for Patients With Symptomatic Peripheral Artery Disease: A Science Advisory From the American Heart Association

Patients with lower-extremity peripheral artery disease (PAD) have greater functional impairment, faster functional decline, increased rates of mobility loss, and poorer quality of life than people without PAD. Supervised exercise therapy (SET) improves walking ability, overall functional status, and health-related quality of life in patients with symptomatic PAD. In 2017, the Centers for Medicare & Medicaid Services released a National Coverage Determination (CAG-00449N) for SET programs for patients with symptomatic PAD. This advisory provides a practical guide for delivering SET programs to patients with PAD according to Centers for Medicare & Medicaid Services criteria. It summarizes the Centers for Medicare & Medicaid Services process and requirements for referral and coverage of SET and provides guidance on how to implement SET for patients with PAD, including the SET protocol, options for outcome measurement, and transition to home-based exercise. This advisory is based on the guidelines established by the Centers for Medicare & Medicaid Services for Medicare beneficiaries in the United States and is intended to assist clinicians and administrators who are implementing SET programs for patients with PAD.

Sitagliptin improves diastolic cardiac function but not cardiorespiratory fitness in adults with type 2 diabetes

BACKGROUND

People with type 2 diabetes mellitus (T2D) have preclinical cardiac and vascular dysfunction associated with low cardiorespiratory fitness (CRF). This is especially concerning because CRF is a powerful predictor of cardiovascular mortality, a primary issue in T2D management. Glucagon-like pepetide-1 (GLP-1) augments cardiovascular function and our previous data in rodents demonstrate that potentiating the GLP-1 signal with a dipeptidyl peptidase-4 (DPP4) inhibitor augments CRF. Lacking are pharmacological treatments which can target T2D-specific physiological barriers to exercise to potentially permit adaptations necessary to improve CRF and thereby health outcomes in people with T2D. We therefore hypothesized that administration of a DPP4-inhibitor (sitagliptin) would improve CRF in adults with T2D.

METHODS AND RESULTS

Thirty-eight participants (64 ± 1 years; mean ± SE) with T2D were randomized in a double-blinded study to receive 100 mg/day sitagliptin, 2 mg/day glimepiride, or placebo for 3 months after baseline measurements. Fasting glucose decreased with both glimepiride and sitagliptin compared with placebo (P = 0.002). CRF did not change in any group (Placebo: Pre: 15.4 ± 0.9 vs. Post: 16.1 ± 1.1 ml/kg/min vs. Glimepiride: 18.5 ± 1.0 vs. 17.7 ± 1.2 ml/kg/min vs. Sitagliptin: 19.1 ± 1.2 vs. 18.3 ± 1.1 ml/kg/min; P = 0.3). Sitagliptin improved measures of cardiac diastolic function, however, measures of vascular function did not change with any treatment.

CONCLUSIONS

Three months of sitagliptin improved diastolic cardiac function, however, CRF did not change. These data suggest that targeting the physiological contributors to CRF with sitagliptin alone is not an adequate strategy to improve CRF in people with T2D.

CLINICAL TRIALS REGISTRATION

www.clinicaltrials.gov NCT01951339.

Home-Based Cardiac Rehabilitation: A Scientific Statement From the American Association of Cardiovascular and Pulmonary Rehabilitation, the American Heart Association, and the American College of Cardiology

Cardiac rehabilitation (CR) is an evidence-based intervention that uses patient education, health behavior modification, and exercise training to improve secondary prevention outcomes in patients with cardiovascular disease. CR programs reduce morbidity and mortality rates in adults with ischemic heart disease, heart failure, or cardiac surgery but are significantly underused, with only a minority of eligible patients participating in CR in the United States. New delivery strategies are urgently needed to improve participation. One potential strategy is home-based CR (HBCR). In contrast to center-based CR services, which are provided in a medically supervised facility, HBCR relies on remote coaching with indirect exercise supervision and is provided mostly or entirely outside of the traditional center-based setting. Although HBCR has been successfully deployed in the United Kingdom, Canada, and other countries, most US healthcare organizations have little to no experience with such programs. The purpose of this scientific statement is to identify the core components, efficacy, strengths, limitations, evidence gaps, and research necessary to guide the future delivery of HBCR in the United States. Previous randomized trials have generated low- to moderate-strength evidence that HBCR and center-based CR can achieve similar improvements in 3- to 12-month clinical outcomes. Although HBCR appears to hold promise in expanding the use of CR to eligible patients, additional research and demonstration projects are needed to clarify, strengthen, and extend the HBCR evidence base for key subgroups, including older adults, women, underrepresented minority groups, and other higher-risk and understudied groups. In the interim, we conclude that HBCR may be a reasonable option for selected clinically stable low- to moderate-risk patients who are eligible for CR but cannot attend a traditional center-based CR program.

Home-Based Cardiac Rehabilitation: A Scientific Statement From the American Association of Cardiovascular and Pulmonary Rehabilitation, the American Heart Association, and the American College of Cardiology

Cardiac rehabilitation (CR) is an evidence-based intervention that uses patient education, health behavior modification, and exercise training to improve secondary prevention outcomes in patients with cardiovascular disease. CR programs reduce morbidity and mortality rates in adults with ischemic heart disease, heart failure, or cardiac surgery but are significantly underused, with only a minority of eligible patients participating in CR in the United States. New delivery strategies are urgently needed to improve participation. One potential strategy is home-based CR (HBCR). In contrast to center-based CR services, which are provided in a medically supervised facility, HBCR relies on remote coaching with indirect exercise supervision and is provided mostly or entirely outside of the traditional center-based setting. Although HBCR has been successfully deployed in the United Kingdom, Canada, and other countries, most US healthcare organizations have little to no experience with such programs. The purpose of this scientific statement is to identify the core components, efficacy, strengths, limitations, evidence gaps, and research necessary to guide the future delivery of HBCR in the United States. Previous randomized trials have generated low- to moderate-strength evidence that HBCR and center-based CR can achieve similar improvements in 3- to 12-month clinical outcomes. Although HBCR appears to hold promise in expanding the use of CR to eligible patients, additional research and demonstration projects are needed to clarify, strengthen, and extend the HBCR evidence base for key subgroups, including older adults, women, underrepresented minority groups, and other higher-risk and understudied groups. In the interim, we conclude that HBCR may be a reasonable option for selected clinically stable low- to moderate-risk patients who are eligible for CR but cannot attend a traditional center-based CR program.

Impact of diabetes and sex in heart failure with reduced ejection fraction patients from the ASIAN-HF registry

AIMS

To examine sex differences in clinical characteristics, echocardiographic features, quality of life and 1-year death or heart failure (HF) hospitalization outcomes in patients with/without diabetes mellitus (DM).

METHODS AND RESULTS

Utilizing the Asian Sudden Cardiac Death in HF (ASIAN-HF) registry, 5255 patients (mean age 59.6 ± 13.1, 78% men) with symptomatic HF with reduced ejection fraction (HFrEF) were stratified by DM status to address the research aims. Despite similar prevalence of DM between Asian men (43%) and women (42%), the odds of DM increased at lower body mass index in women vs. men (≥ 23 vs. ≥ 27.5 kg/m² , P_interaction  = 0.014). DM was more strongly related to chronic kidney disease in women vs. men [adjusted odds ratio (OR) 1.85, 95% confidence interval (CI) 1.33-2.57 vs. OR 1.32, 95% CI 1.11-1.56, P_interaction  = 0.009]. Sex also modified the relationship between DM and left ventricular geometry (P_interaction  = 0.003), whereby DM was associated with a more concentric left ventricular geometry in women than men. Women had lower quality of life than men (P < 0.001), in both DM and non-DM groups. DM was associated with worse composite outcomes at 1 year in women vs. men [hazard ratio (HR) 1.79, 95% CI 1.24-2.60 vs. HR 1.32, 95% CI 1.12-1.56; P_interaction  = 0.005).

CONCLUSIONS

Asian women with HFrEF were more likely to have DM despite a lean body mass index, a greater burden of chronic kidney disease and more concentric left ventricular geometry, compared to men. Furthermore, DM confers worse quality of life, irrespective of sex, and a greater risk of adverse outcomes in women than men. These data underscore the need for sex-specific approaches to diabetes in patients with HF.

Supplemental Oxygen Improves In Vivo Mitochondrial Oxidative Phosphorylation Flux in Sedentary Obese Adults With Type 2 Diabetes

Type 2 diabetes is associated with impaired exercise capacity. Alterations in both muscle perfusion and mitochondrial function can contribute to exercise impairment. We hypothesized that impaired muscle mitochondrial function in type 2 diabetes is mediated, in part, by decreased tissue oxygen delivery and would improve with oxygen supplementation. Ex vivo muscle mitochondrial content and respiration assessed from biopsy samples demonstrated expected differences in obese individuals with (n = 18) and without (n = 17) diabetes. Similarly, in vivo mitochondrial oxidative phosphorylation capacity measured in the gastrocnemius muscle via ³¹P-MRS indicated an impairment in the rate of ADP depletion with rest (27 ± 6 s [diabetes], 21 ± 7 s [control subjects]; P = 0.008) and oxidative phosphorylation (P = 0.046) in type 2 diabetes after isometric calf exercise compared with control subjects. Importantly, the in vivo impairment in oxidative capacity resolved with oxygen supplementation in adults with diabetes (ADP depletion rate 5.0 s faster, P = 0.012; oxidative phosphorylation 0.046 ± 0.079 mmol/L/s faster, P = 0.027). Multiple in vivo mitochondrial measures related to HbA_1c These data suggest that oxygen availability is rate limiting for in vivo mitochondrial oxidative exercise recovery measured with ³¹P-MRS in individuals with uncomplicated diabetes. Targeting muscle oxygenation could improve exercise function in type 2 diabetes.

Achieving ADA/ISPAD clinical guideline goals is associated with higher insulin sensitivity and cardiopulmonary fitness in adolescents with type 1 diabetes: Results from RESistance to InSulin in Type 1 ANd Type 2 diabetes (RESISTANT) and Effects of MEtformin on CardiovasculaR Function in AdoLescents with Type 1 Diabetes (EMERALD) Studies

OBJECTIVE

Most youth with type 1 diabetes do not meet the American Diabetes Association (ADA) and International Society for Pediatric and Adolescent Diabetes (ISPAD) targets for hemoglobin A1c (HbA1c), blood pressure (BP), lipids, and body mass index (BMI). We hypothesized that ISPAD/ADA goal achievement would be associated with better insulin sensitivity (IS) and cardiopulmonary fitness.

METHODS

IS was quantified as glucose infusion rate (GIR) from a hyperinsulinemic-euglycemic clamp in youth with type 1 diabetes from the RESistance to InSulin in Type 1 ANd Type 2 diabetes (RESISTANT) (n = 86) and Effects of MEtformin on CardiovasculaR Function in AdoLescents with Type 1 Diabetes (EMERALD) (n = 41) cohorts (n = 127; age 15.7 ± 2.2 years, 52% girls). Cardiopulmonary fitness was measured as peak oxygen consumption (VO₂ peak/kg) during upright (RESISTANT) or supine (EMERALD) cycle ergometry and were stratified by cycle type. Goal achievement was defined as HbA1c < 7.5%, BP < 90th percentile, LDL-cholesterol < 100 mg/dL, HDL-cholesterol > 35 mg/dL, triglycerides < 150 mg/dL and BMI < 85th percentile. Participants were stratified into 3 groups: achieving 0-3 goals (n = 52), 4 goals (n = 48), and 5-6 goals (n = 27). Differences between groups were examined with generalized linear models.

RESULTS

IS was lower in youth who met 0-3 goals (5.2 ± 3.4 mg/kg/min) vs those who met 4 goals (7.4 ± 4.1 mg/kg/min, P = .04) and those who met 5-6 goals (8.5 ± 4.3 mg/kg/min, P = .003), and remained significant after adjustments for sex and diabetes duration. Upright VO₂ peak was lower in youth who met 0-3 goals (25.8 ± 4.6 mL/kg/min) vs those who met 4 goals (33.0 ± 7.8 mL/kg/min, P = .01) and those who met 5-6 goals (33.2 ± 4.4 mL/kg/min, P = .004). Similar and significant relationships were observed in EMERALD participants for supine VO₂ peak.

CONCLUSIONS

ADA/ISPAD goal achievement was associated with greater IS and cardiopulmonary fitness.

Mechanisms of Aerobic Exercise Impairment in Diabetes: A Narrative Review

The prevalence of diabetes in the United States and globally has been rapidly increasing over the last several decades. There are now estimated to be 30.3 million people in the United States and 422 million people worldwide with diabetes. Diabetes is associated with a greatly increased risk of cardiovascular mortality, which is the leading cause of death in adults with diabetes. While exercise training is a cornerstone of diabetes treatment, people with diabetes have well-described aerobic exercise impairments that may create an additional diabetes-specific barrier to adding regular exercise to their lifestyle. Physiologic mechanisms linked to exercise impairment in diabetes include insulin resistance, cardiac abnormalities, mitochondrial function, and the ability of the body to supply oxygen. In this paper, we highlight the abnormalities of exercise in type 2 diabetes as well as potential therapeutic approaches.

Identifying the Critical Gaps in Research on Sex Differences in Metabolism Across the Life Span

The National Institutes of Health (NIH) Office of Research in Women's Health now functions under a mandate calling for the systematic inclusion of both female and male cells, animals, and human subjects in all types of research, so that sex as a biological variable is understood in health and disease. Sex-specific data can improve disease prevention, diagnosis, and treatment as well as reduce inequities. Inclusion of women in research studies has modestly improved over the last 20 years, yet preclinical research is still primarily done using male animal models and male-derived cells, with the result that many conclusions are made based on incomplete and sex-biased data. There are important, yet poorly studied, sex differences in cardiometabolic disease. To begin to address these sex differences, the Center for Women's Health Research at the University of Colorado held its inaugural National Conference, "Sex Differences Across the Lifespan: A Focus on Metabolism," in September 2016 (cwhr@ucdenver.edu). Research to address the important goal of understanding key sex differences in cardiometabolic disease across the life span is lacking. The goal of this article is to discuss the current state of research addressing sex differences in cardiometabolic health across the life span, to outline critical research gaps that must be addressed in response to NIH mandates, and, importantly, to develop strategies to address sex as a biological variable to understand disease mechanisms as well as develop diagnostic and therapeutic modalities.

Acute vitamin C improves cardiac function, not exercise capacity, in adults with type 2 diabetes

BACKGROUND

People with type 2 diabetes (T2D) have impaired exercise capacity, even in the absence of complications, which is predictive of their increased cardiovascular mortality. Cardiovascular dysfunction is one potential cause of this exercise defect. Acute infusion of vitamin C has been separately shown to improve diastolic and endothelial function in prior studies. We hypothesized that acute vitamin C infusion would improve exercise capacity and that these improvements would be associated with improved cardiovascular function.

METHODS

Adults with T2D (n = 31, 7 female, 24 male, body mass index (BMI): 31.5 ± 0.8 kg/m²) and BMI-similar healthy adults (n = 21, 11 female, 10 male, BMI: 30.4 ± 0.7 kg/m²) completed two randomly ordered visits: IV infusion of vitamin C (7.5 g) and a volume-matched saline infusion. During each visit peak oxygen uptake (VO₂peak), brachial artery flow mediated dilation (FMD), reactive hyperemia (RH; plethysmography), and cardiac echocardiography were measured. General linear mixed models were utilized to assess the differences in all study variables.

RESULTS

Acute vitamin C infusion improved diastolic function, assessed by lateral and septal E:E' (P < 0.01), but did not change RH (P = 0.92), or VO₂peak (P = 0.33) in any participants.

CONCLUSION

Acute vitamin C infusion improved diastolic function but did not change FMD, forearm reactive hyperemia, or peak exercise capacity. Future studies should further clarify the role of endothelial function as well as other possible physiological causes of exercise impairment in order to provide potential therapeutic targets.Trial registration NCT00786019. Prospectively registered May 2008.