The role of insulin resistance in the association between body fat and autonomic function

The characteristics of elevated blood pressure in abdominal obesity correspond to primary hypertension: a cross-sectional study

BACKGROUND

Obesity-related hypertension and the associated metabolic abnormalities are considered as a distinct hypertensive phenotype. Here we examined how abdominal fat content, as judged by waist:height ratio, influenced blood pressure and hemodynamic profile in normotensive subjects and never-treated hypertensive patients.

METHODS

The 541 participants (20-72 years) underwent physical examination and laboratory analyses and were divided into age and sex-adjusted quartiles of waist:height ratio. Supine hemodynamics were recorded using whole-body impedance cardiography, combined with analyses of radial tonometric pulse wave form and heart rate variability.

RESULTS

Mean waist:height ratios in the quartiles were 0.46, 0.51, 0.55 and 0.62. Radial and aortic blood pressure, systemic vascular resistance, pulse wave velocity, markers of glucose and lipid metabolism, leptin levels and C-reactive protein were higher in quartile 4 when compared with quartiles 1 and 2 (p < 0.05 for all). Cardiac index was lower in quartile 4 versus quartile 1, while no differences were seen in heart rate variability, augmentation index, plasma renin activity, and aldosterone concentration between the quartiles. Linear regression analyses showed independent associations of abdominal obesity with higher aortic systolic and diastolic blood pressure, systemic vascular resistance, and pulse wave velocity (p < 0.05 for waist:height ratio in all regression models).

CONCLUSION

Higher waist:height ratio was associated with elevated blood pressure, systemic vascular resistance, and arterial stiffness, but not with alterations in cardiac sympathovagal modulation or activation of the circulating renin-angiotensin-aldosterone system. Although obesity-related elevation of blood pressure has distinct phenotypic features, these results suggest that its main characteristics correspond those of primary hypertension.

TRIAL REGISTRATION

ClinicalTrails.gov NCT01742702 (date of registration 5th December 2012).

Dietary Supplement Intake is Associated with Healthier Lifestyle Behaviors in College Students Attending a Regional University in the Southeast: A Cross-Sectional Study

The relationship between intake of dietary supplements and biomarkers such as insulin and insulin-like growth factor has not been well explored. The primary aim of this cross-sectional study was to investigate the associations between supplement intake and biological and lifestyle factors. We hypothesized that dietary supplement intake was associated with healthier lifestyle behaviors. College students attending a Southeast university were recruited between January 2018 and April 2019. Blood samples were collected to measure insulin, insulin-like growth factor 1 (IGF-1) and alanine aminotransferase (ALT). Statistical tests employed were linear regression and analysis of variance. Ninety-eight participants completed the study and 91% reported taking at least one supplement, while 5.1% reported taking 9+ supplements once per week. There were no differences in levels of insulin, IGF-1 and ALT by levels of dietary supplement intake. Although there were no differences in HEI-2015 score among the groups, those who consumed five or more supplements met a higher percentage of the recommended intake for fruits, performed aerobic exercise for longer duration, and had lower body fat percentage compared to participants who consumed two or less supplements at least once per week. These findings are consistent with previous studies and suggest that dietary supplement intake is highly prevalent in college students, and it may be related to healthy lifestyle behaviors. Future studies should employ mixed methodology to examine reasons by which college students consume dietary supplements and to assess perceived and direct health benefits associated with consumption.

Elevated heart rate as sympathetic biomarker in human obesity

BACKGROUND AND AIM

The present study was aimed at determining whether and to what extent a specific heart rate (HR) cutoff value allows to identify in obeses a more pronounced level of adrenergic overdrive.

METHODS AND RESULTS

In 86 obese subjects aged 44.7 ± 0.9 (mean ± SEM) years and in 45 heathy lean controls of similar age we evaluated muscle sympathetic nerve traffic (MSNA, microneurography) and venous plasma norepinephrine (NE, HPLC assay), subdividing the subjects in 3 different groups according to their resting clinic and 24-h HR values (<70, 70-79 and 80-89 beats/minute). MSNA and plasma NE values detected in the three obese groups were almost superimposable each other, no significant difference between groups being observed. A similar behavior was observed when HR values were assessed during the 24-h Holter monitoring. In the group as a whole no significant relationship was detected between MSNA, plasma NE and clinic HR, this being the case also when 24-h HR replaced clinic HR in the correlation analysis. In contrast lean controls displayed a progressive significant increase in MSNA values form the group with clinic (and 24 Holter) values below 70 beats/minute to the ones with HR values between 70 and 79 and above 80 beats/minute.

CONCLUSIONS

In the obese state measurement of resting HR may allow to provide some general information on the functional status of the adrenergic cardiovascular drive. When the information required, however, are more subtle the sensitivity of the approach appears to be reduced and HR cannot be regarded as a faithful sympathetic biomarker.

Development and Validation of an Insulin Resistance Predicting Model Using a Machine-Learning Approach in a Population-Based Cohort in Korea

Background: Insulin resistance is a common etiology of metabolic syndrome, but receiver operating characteristic (ROC) curve analysis shows a weak association in Koreans. Using a machine learning (ML) approach, we aimed to generate the best model for predicting insulin resistance in Korean adults aged > 40 of the Ansan/Ansung cohort using a machine learning (ML) approach. Methods: The demographic, anthropometric, biochemical, genetic, nutrient, and lifestyle variables of 8842 participants were included. The polygenetic risk scores (PRS) generated by a genome-wide association study were added to represent the genetic impact of insulin resistance. They were divided randomly into the training (n = 7037) and test (n = 1769) sets. Potentially important features were selected in the highest area under the curve (AUC) of the ROC curve from 99 features using seven different ML algorithms. The AUC target was ≥0.85 for the best prediction of insulin resistance with the lowest number of features. Results: The cutoff of insulin resistance defined with HOMA-IR was 2.31 using logistic regression before conducting ML. XGBoost and logistic regression algorithms generated the highest AUC (0.86) of the prediction models using 99 features, while the random forest algorithm generated a model with 0.82 AUC. These models showed high accuracy and k-fold values (>0.85). The prediction model containing 15 features had the highest AUC of the ROC curve in XGBoost and random forest algorithms. PRS was one of 15 features. The final prediction models for insulin resistance were generated with the same nine features in the XGBoost (AUC = 0.86), random forest (AUC = 0.84), and artificial neural network (AUC = 0.86) algorithms. The model included the fasting serum glucose, ALT, total bilirubin, HDL concentrations, waist circumference, body fat, pulse, season to enroll in the study, and gender. Conclusion: The liver function, regular pulse checking, and seasonal variation in addition to metabolic syndrome components should be considered to predict insulin resistance in Koreans aged over 40 years.

Heart Rate and Heart Rate Variability Changes Are Not Related to Future Cardiovascular Disease and Death in People With and Without Dysglycemia: A Downfall of Risk Markers? The Whitehall II Cohort Study

OBJECTIVE

Higher resting heart rate (rHR) and lower heart rate variability (HRV) are associated with increased risk of cardiovascular disease (CVD) and all-cause mortality in people with and without diabetes. It is unknown whether temporal changes in rHR and HRV may contribute to this risk. We investigated associations between 5-year changes in rHR and HRV and risk of future CVD and death, taking into account participants' baseline glycemic state.

RESEARCH DESIGN AND METHODS

In this prospective, population-based cohort study we investigated 4,611 CVD-free civil servants (mean [SD] age, 60 [5.9] years; 70% men). We measured rHR and/or six indices of HRV. Associations of 5-year change in 5-min rHR and HRV with fatal and nonfatal CVD and all-cause mortality or the composite of the two were assessed, with adjustments made for relevant confounders. Effect modification by glycemic state was tested.

RESULTS

At baseline, 63% of participants were normoglycemic, 29% had prediabetes, and 8% had diabetes. During a median (interquartile range) follow-up of 11.9 (11.4; 12.3) years, 298 participants (6.5%) experienced a CVD event and 279 (6.1%) died of non-CVD-related causes. We found no association between 5-year changes in rHR and HRV and future events. Only baseline rHR was associated with all-cause mortality. A 10 bpm-higher baseline HR level was associated with an 11.4% higher rate of all-cause mortality (95% CI 1.0-22.9%; P = 0.032). Glycemic state did not modify associations.

CONCLUSIONS

Changes in rHR and HRV and possibly also baseline values of these measures are not associated with future CVD or death in people with or without dysglycemia.

Ideal cardiovascular health and resting heart rate in the Multi-Ethnic Study of Atherosclerosis

Elevated resting heart rate (RHR) is associated with an increased cardiovascular disease (CVD) risk, but little is known about its association with cardiovascular health (CVH), assessed by the Life's Simple 7 (LS7) metrics. We explored whether ideal CVH was associated with RHR in a cohort free from clinical CVD. We conducted a cross-sectional analysis of baseline data (2000-2002) of 6457 Multi-Ethnic Study of Atherosclerosis participants in 2018. Each LS7 metric (smoking, physical activity, diet, body mass index, blood pressure, cholesterol and glucose) was scored 0-2. Total score ranged from 0 to 14. Scores of 0-8 indicate inadequate, 9-10 average, and 11-14 optimal CVH. RHR was categorized as <60, 60-69, 70-79 and ≥80 bpm. We used multinomial logistic regression to determine associations between CVH score and RHR, adjusting for age, sex, race/ethnicity, education, income, health insurance, and atrioventricular nodal blockers. Mean age of participants (standard deviation) was 62 (10) years; 53% were women; 47% had inadequate CVH, 33% average, and 20% optimal. Favorable CVH was associated with lower odds of having higher RHR. Compared to RHR <60 bpm, participants with optimal CVH had adjusted odds ratio (95% CI) of 0.55 (0.46-0.64) for RHR of 60-69 bpm, 0.34 (0.28-0.43) for 70-79 bpm, and 0.14 (0.09-0.22) for ≥80 bpm. A similar pattern was observed in the stratified analysis by sex, race/ethnicity and age. Favorable CVH was less likely to be associated with elevated RHR irrespective of sex, race/ethnicity and age. More research is needed to explore the usefulness of promoting ideal CVH to reduce elevated RHR, a known risk factor for CVD.

Relationship of the Aggregation of Cardiovascular Risk Factors in the Parasympathetic Modulation of Young People with Type 1 Diabetes

Background and objectives: In healthy individuals, autonomic alterations are associated with the aggregation of cardiovascular risk factors. However, in individuals with type 1 diabetes, who are known to present autonomic alterations, mainly characterized by a reduction in parasympathetic modulation, these associations have not yet been investigated. We assess whether the aggregation of cardiovascular risk factors influences parasympathetic indices of heart rate variability in young people with type 1 diabetes. Materials and methods: This cross-sectional study included 39 individuals with type 1 diabetes (22.54 ± 4.31), evaluated in relation to the risk factors: blood pressure, fat percentage, and resting heart rate. For heart rate variability analysis, heart rate was recorded beat-to-beat using a cardio frequency meter (PolarS810i) for 30 min with the volunteers in dorsal decubitus. The parasympathetic heart rate variability indices were calculated: rMSSD, pNN50, high frequency (HF) n.u (normalized units), SD1, 2LV, and 2ULV. Data collection was carried out in 2014 and analyzed in 2017. Results: Individuals with two aggregate risk factors present a reduction in the values of the indices that reflect parasympathetic autonomic modulation compared to individuals without the risk factors analyzed, regardless of sex and age. Conclusion: In young people with type 1 diabetes, the aggregation of cardiovascular risk factors is associated with parasympathetic autonomic impairment.

Heart Rate, Autonomic Function, and Future Changes in Glucose Metabolism in Individuals Without Diabetes: The Whitehall II Cohort Study

OBJECTIVE

Autonomic nervous system dysfunction is associated with impaired glucose metabolism, but the temporality of this association remains unclear in individuals without diabetes. We investigated the association of autonomic function with 5-year changes in glucose metabolism in individuals without diabetes.

RESEARCH DESIGN AND METHODS

Analyses were based on 9,000 person-examinations for 3,631 participants without diabetes in the Whitehall II cohort. Measures of autonomic function included 5-min resting heart rate and six heart rate variability (HRV) indices. Associations between baseline autonomic function measures and 5-year changes in fasting and 2-h plasma glucose, serum insulin concentrations, insulin sensitivity (insulin sensitivity index [ISI0-120] and HOMA of insulin sensitivity), and β-cell function (HOMA of β-cell function) were estimated in models adjusting for age, sex, ethnicity, metabolic factors, and medication.

RESULTS

A 10-bpm higher resting heart rate was associated with 5-year changes in fasting and 2-h insulin and ISI0-120 of 3.3% change (95% CI 1.8; 4.8), P < 0.001; 3.3% change (1.3; 5.3), P = 0.001; and -1.4% change (-2.4; -0.3), P = 0.009, respectively. In models adjusted for age, sex, and ethnicity, higher baseline values of several HRV indices were associated with a 5-year decrease in fasting and 2-h insulin and ISI0-120. However, significance was lost by full adjustment. A majority of HRV indices exhibited a trend toward higher values being associated with lower insulin levels and higher insulin sensitivity.

CONCLUSIONS

Higher resting heart rate in individuals without diabetes is associated with future unfavorable changes in insulin levels and insulin sensitivity. Associations may be mediated via autonomic function; however, results are inconclusive. Resting heart rate may be a risk marker for future pathophysiological changes in glucose metabolism.

Is the Brain a Key Player in Glucose Regulation and Development of Type 2 Diabetes?

Ever since Claude Bernards discovery in the mid 19th-century that a lesion in the floor of the third ventricle in dogs led to altered systemic glucose levels, a role of the CNS in whole-body glucose regulation has been acknowledged. However, this finding was later overshadowed by the isolation of pancreatic hormones in the 20th century. Since then, the understanding of glucose homeostasis and pathology has primarily evolved around peripheral mechanism. Due to scientific advances over these last few decades, however, increasing attention has been given to the possibility of the brain as a key player in glucose regulation and the pathogenesis of metabolic disorders such as type 2 diabetes. Studies of animals have enabled detailed neuroanatomical mapping of CNS structures involved in glucose regulation and key neuronal circuits and intracellular pathways have been identified. Furthermore, the development of neuroimaging techniques has provided methods to measure changes of activity in specific CNS regions upon diverse metabolic challenges in humans. In this narrative review, we discuss the available evidence on the topic. We conclude that there is much evidence in favor of active CNS involvement in glucose homeostasis but the relative importance of central vs. peripheral mechanisms remains to be elucidated. An increased understanding of this field may lead to new CNS-focusing pharmacologic strategies in the treatment of type 2 diabetes.

Metabolic syndrome is associated with decreased heart rate variability in a sex-dependent manner: a comparison between 252 men and 249 women

Impaired heart rate variability (HRV) is associated with increased risk of cardiovascular disease, but evidence regarding alterations of HRV in metabolic syndrome (MetS) remains elusive. In order to examine HRV in MetS, we subjected 501 volunteers without atherosclerosis, diabetes or antihypertensive medication, mean age 48 years, to passive head-up tilt. The subjects were divided to control men (n = 131), men with MetS (n = 121), control women (n = 191) and women with MetS (n = 58) according to the criteria by Alberti et al. (Circulation, 2009, 120, 1640). In unadjusted analyses (i) men and women with MetS had lower total power and high-frequency (HF) power of HRV than controls whether supine or upright (P<0·05 for all). (ii) Supine low-frequency (LF) power of HRV was lower in men (P = 0·012) but not in women (P = 0·064) with MetS than in controls, while men and women with MetS had lower upright LF power of HRV than controls (P <0·01 for both). (iii) The LF:HF ratio did not differ between subjects with and without MetS. After adjustment for age, smoking habits, alcohol intake, height, heart rate and breathing frequency, only the differences in upright total power and HF power of HRV between women with MetS and control women remained significant (P<0·05). In conclusion, reduced total and HF power of HRV in the upright position may partially explain why the relative increase in cardiovascular risk associated with MetS is greater in women than in men. Additionally, the present results emphasize that the confounding factors must be carefully taken into consideration when evaluating HRV.

Effects of aerobic or resistance exercise training on cardiovascular autonomic function of subjects with type 2 diabetes: A pilot study

BACKGROUND AND AIMS

Both aerobic (AER) and resistance (RES) training improve metabolic control in patients with type 2 diabetes (T2DM). However, information on the effects of these training modalities on cardiovascular autonomic control is limited. Our aim was to compare the effects of AER and RES training on cardiovascular autonomic function in these subjects.

METHODS AND RESULTS

Cardiovascular autonomic control was assessed by Power Spectral Analysis (PSA) of Heart Rate Variability (HRV) and baroreceptors function indexes in 30 subjects with T2DM, randomly assigned to aerobic or resistance training for 4 months. In particular, PSA of HRV measured the Low Frequency (LF) and High Frequency (HF) bands of RR variations, expression of prevalent sympathetic and parasympathetic drive, respectively. Furthermore, we measured the correlation occurring between systolic blood pressure and heart rate during a standardized Valsalva maneuver using two indexes, b2 and b4, considered an expression of baroreceptor sensitivity and peripheral vasoactive adaptations during predominant sympathetic and parasympathetic drive, respectively. After training, the LF/HF ratio, which summarizes the sympatho-vagal balance in HRV control, was similarly decreased in the AER and RES groups. After AER, b2 and b4 significantly improved. After RES, changes of b2 were of borderline significance, whereas changes of b4 did not reach statistical significance. However, comparison of changes in baroreceptor sensitivity indexes between groups did not show statistically significant differences.

CONCLUSION

Both aerobic and resistance training improve several indices of the autonomic control of the cardiovascular system in patients with T2DM. Although these improvements seem to occur to a similar extent in both training modalities, some differences cannot be ruled out.

CLINICAL TRIAL REGISTRATION NUMBER

NCT01182948, clinicaltrials.gov.

The relationship between erythrocyte membrane fatty acid levels and cardiac autonomic function in obese children

OBJECTIVE

Childhood obesity is a worldwide health concern. Studies have shown autonomic dysfunction in obese children. The exact mechanism of this dysfunction is still unknown. The aim of this study was to assess the relationship between erythrocyte membrane fatty acid (EMFA) levels and cardiac autonomic function in obese children using heart rate variability (HRV).

METHODS

A total of 48 obese and 32 healthy children were included in this case-control study. Anthropometric and biochemical data, HRV indices, and EMFA levels in both groups were compared statistically.

RESULTS

HRV parameters including standard deviation of normal-to-normal R-R intervals (NN), root mean square of successive differences, the number of pairs of successive NNs that differ by >50 ms (NN50), the proportion of NN50 divided by the total number of NNs, high-frequency power, and low-frequency power were lower in obese children compared to controls, implying parasympathetic impairment. Eicosapentaenoic acid and docosahexaenoic acid levels were lower in the obese group (p<0.001 and p=0.012, respectively). In correlation analysis, in the obese group, body mass index standard deviation and linoleic acid, arachidonic acid, triglycerides, and high-density lipoprotein levels showed a linear correlation with one or more HRV parameter, and age, eicosapentaenoic acid, and systolic and diastolic blood pressure correlated with mean heart rate. In linear regression analysis, age, dihomo-gamma-linolenic acid, linoleic acid, arachidonic acid, body mass index standard deviation, systolic blood pressure, triglycerides, low-density lipoprotein and high-density lipoprotein were related to HRV parameters, implying an effect on cardiac autonomic function.

CONCLUSION

There is impairment of cardiac autonomic function in obese children. It appears that levels of EMFAs such as linoleic acid, arachidonic acid and dihomo-gamma-linolenic acid play a role in the regulation of cardiac autonomic function in obese children.