Jacqueline Hay

Physical activity intensity and cardiometabolic risk in youth.

OBJECTIVE To determine the association between physical activity (PA) intensities and cardiometabolic risk factors in youth. DESIGN Cross-sectional study using data from the 2008 Healthy Hearts Prospective Cohort Study of Physical Activity and Cardiometabolic Health in Youth. SETTING Rural and urban communities in Alberta, Canada. PARTICIPANTS A convenience sample of 605 youth aged 9 to 17 years. Youth were on average aged 12.1 years, 248 were boys (41%), and 157 were overweight or obese (26%). MAIN EXPOSURE Actical accelerometer-measured PA intensity. MAIN OUTCOMES MEASURES The primary outcome was body mass index (calculated as weight in kilograms divided by height in meters squared) z score. Secondary outcome measures included waist circumference, systolic blood pressure, and cardiorespiratory fitness (maximal oxygen consumption [[Vdot]O2max]). RESULTS Body mass index z score, waist circumference, and systolic blood pressure decreased and [Vdot]O2max increased in a dose-response manner across tertiles of vigorous PA (adjusted P < .001). No significant differences in cardiometabolic risk factors were seen across tertiles of moderate or light PA in multivariable analyses. Achieving more than 7 minutes of vigorous PA daily was associated with a reduced adjusted odds ratio of overweight status (0.56; 95% CI, 0.33-0.95) and elevated systolic blood pressure (0.36; 95% CI, 0.16-0.79). The odds of overweight status and elevated blood pressure decreased with increasing time and intensity of PA. CONCLUSIONS Only vigorous PA was consistently associated with lower levels of waist circumference, body mass index z score, systolic blood pressure, and increased cardiorespiratory fitness in youth. These findings underscore the importance of vigorous PA in guidelines for children and adolescents.

Dietary determinants of hepatic steatosis and visceral adiposity in overweight and obese youth at risk of type 2 diabetes

BACKGROUND Dietary determinants of hepatic steatosis, an important precursor for nonalcoholic fatty liver disease, are undefined. OBJECTIVE We explored the roles of sugar and fat intake as determinants of hepatic steatosis and visceral obesity in overweight adolescents at risk of type 2 diabetes. DESIGN This was a cross-sectional study of dietary patterns and adipose tissue distribution in 74 overweight adolescents (aged: 15.4 ± 1.8 y; body mass index z score: 2.2 ± 0.4). Main outcome measures were hepatic steatosis (≥5.5% fat:water) measured by magnetic resonance spectroscopy and visceral obesity (visceral-to-subcutaneous adipose tissue ratio ≥0.25) measured by magnetic resonance imaging. Main exposure variables were dietary intake and habits assessed by the Harvard Youth Adolescent Food Frequency Questionnaire. RESULTS Hepatic steatosis and visceral obesity were evident in 43% and 44% of the sample, respectively. Fried food consumption was more common in adolescents with hepatic steatosis than in adolescents without hepatic steatosis (41% compared with 18%; P = 0.04). Total fat intake (β = 0.51, P = 0.03) and the consumption of >35% of daily energy intake from fat (OR: 11.8; 95% CI: 1.6, 86.6; P = 0.02) were both positively associated with hepatic steatosis. Available carbohydrate (β = 0.54, P = 0.02) and the frequent consumption of soda were positively associated with visceral obesity (OR: 6.4; 95% CI: 1.2, 34.0; P = 0.03). Daily fiber intake was associated with reduced odds of visceral obesity (OR: 0.82; 95% CI: 0.68, 0.98; P = 0.02) but not hepatic steatosis. CONCLUSION Hepatic steatosis is associated with a greater intake of fat and fried foods, whereas visceral obesity is associated with increased consumption of sugar and reduced consumption of fiber in overweight and obese adolescents at risk of type 2 diabetes.

A systematic review and meta-analysis of exercise interventions in adults with type 1 diabetes

AIMS Conflicting evidence exists regarding the benefits of physical activity for long-term blood glucose control in adults with type 1 diabetes (T1D). The object of this systematic review was to determine the effects of physical activity on long-term blood glucose control in T1D adults. METHODS PubMed/Medline, Embase, CENTRAL, SPORTdiscus, Global Health and ICTRP were searched up to October 2013 for randomized trials of aerobic or resistance exercise training in T1D adults. Exercises had to be performed at least twice weekly for a minimum of two months. The primary outcome was glycated hemoglobin (HbA1c). Secondary outcomes included cardiorespiratory fitness and insulin dose. RESULTS Six randomized trials were identified (323 adults); sample sizes ranged from n=6 to n=148 participants receiving the intervention. Five trials had an unknown risk of bias; one trial was deemed to be at high risk of bias. Exercise frequency varied from twice weekly to daily, with intensities (50-90% VO2peak), and session durations (20-120 min) varying widely. Four trials reported HbA1c, which decreased with exercise training (mean difference [MD] -0.78% (-9 mmol/mol), 95% CI -1.14 (-13 mmol/mol) to -0.41 (-5 mmol/mol); p<0.0001; I(2) 0%) compared with controls. Exercise training improved cardiorespiratory fitness by 3.45 ml/kg/min (95% CI 0.59 to 6.31, p=0.02, I(2) 0%) compared with controls. One trial reported an effect on insulin dose (MD -0.4U/kg, 95% CI -0.53 to -0.27, p<0.00001) compared to controls. CONCLUSION There are currently insufficient well-designed studies to ascertain the true effect of exercise training on HbA1c in individuals with T1D, but current results are promising.

Cardiorespiratory fitness and adiposity in metabolically healthy overweight and obese youth.

OBJECTIVE: Controversy exists surrounding the contribution of fitness and adiposity as determinants of the Metabolically Healthy Overweight (MHO) phenotype in youth. This study investigated the independent contribution of cardiorespiratory fitness and adiposity to the MHO phenotype among overweight and obese youth. METHODS: This cross-sectional study included 108 overweight and obese youth classified as MHO (no cardiometabolic risk factors) or non-MHO (≥1 cardiometabolic risk factor), based on age- and gender-specific cut-points for fasting glucose, triglycerides, high-density lipoprotein cholesterol, systolic and diastolic blood pressure, and hepatic steatosis. RESULTS: Twenty-five percent of overweight and obese youth were classified as MHO. This phenotype was associated with lower BMI z-score (BMI z-score: 1.8 ± 0.3 vs 2.1 ± 0.4, P = .02) and waist circumference (99.7 ± 13.2 vs 106.1 ± 13.7 cm, P = .04) compared with non-MHO youth. When matched for fitness level and stratified by BMI z-score (1.6 ± 0.3 vs 2.4 ± 0.2), the prevalence of MHO was fourfold higher in the low BMI z-score group (27% vs 7%; P = .03). Multiple logistic regression analyses revealed that the best predictor of MHO was the absence of hepatic steatosis even after adjusting for waist circumference (odds ratio 0.57, 95% confidence interval 0.40–0.80) or BMI z-score (odds ratio 0.59, 95% confidence interval 0.43–0.80). CONCLUSIONS: The MHO phenotype was present in 25% of overweight and obese youth and is strongly associated with lower levels of adiposity, and the absence of hepatic steatosis, but not with cardiorespiratory fitness.

Fitness is a determinant of the metabolic response to endurance training in adolescents at risk of type 2 diabetes mellitus

The purpose of this prospective cohort study was to determine whether changes in cardiorespiratory fitness are associated with the metabolic response to endurance training in adolescents at risk of type 2 diabetes mellitus (T2DM).

Physical activity intensity and type 2 diabetes risk in overweight youth: a randomized trial

Background:The chronic effects of high-intensity endurance training on metabolic health outcomes in overweight adolescents remains poorly understood.Objective:To test the hypothesis that high-intensity endurance training (ET) is superior to moderate-intensity ET for improving risk factors for type 2 diabetes in overweight adolescents.Design and methods:In this randomized trial, 106 overweight and obese adolescents (15.2 years; 76% female; 62% Caucasian) were randomly assigned to high-intensity ET (70–85% of heart rate reserve, n=38), moderate-intensity ET (40–55% heart rate reserve; n=32) or control for 6 months (n=36). The primary and secondary outcome measures were insulin sensitivity assessed using a frequently sampled intravenous glucose tolerance test and hepatic triglyceride content with magnetic resonance spectroscopy. Exploratory outcomes were cardiorespiratory fitness, physical activity and MRI and dual x-ray absorptiometry-derived measures of adiposity.Results:The study had 96% retention and attendance was 61±21% and 55±24% in the high- and moderate-intensity ET arms. Intention-to-treat analyses revealed that, at follow-up, insulin sensitivity was not different between high-intensity (−1.0 mU kg−1 min−1; 95% confidence interval (CI): −1.6, +1.4 mU kg−1 min−1) and moderate-intensity (+0.26 mU kg−1 min−1; 95% CI: −1.3, +1.8 mU kg−1 min−1) ET arms compared with controls (interaction, P=0.97). Similarly, hepatic triglyceride at follow-up was not different in high-intensity (−1.7% fat/water (F/W); 95% CI: −7.0, +3.6% F/W) and moderate-intensity (−0.40% FW; 95% CI: −6.0, +5.3% F/W) ET compared with controls. Both high intensity (+4.4 ml per kg-FFM (fat-free mass) per minute; 95% CI: 1.7, 7.1 ml kg-FFM−1 min−1) and moderate intensity (+4.4 ml kg-FFM−1 min−1; 95% CI: 1.6, 7.3 ml kg-FFM−1 min−1) increased cardiorespiratory fitness, relative to controls (interaction P<0.001).Conclusions:ET improves cardiorespiratory fitness among obese adolescents; however, owing to lack of compliance, the influence of exercise intensity on insulin sensitivity and hepatic triglycerides remains unclear.

The Blood Pressure Response to Exercise in Youth with Impaired Glucose Tolerance and Type 2 Diabetes

Type 2 diabetes is associated with hypertension and an increased risk of cardiovascular disease. In adults, blood pressure (BP) responses to exercise are predictive of these complications. To determine if the hemodynamic response to exercise is exaggerated in youth with dysglycemia (DG) compared with normoglycemic overweight/ obese (OB) and healthy weight (HW) controls a cross-sectional comparison of BP and heart rate (HR) responses to graded exercise to exhaustion in participants was performed. DG and OB youth were matched for age, BMI z-score, height and sex. Systolic (SBP) and diastolic BP (DBP) were measured every 2 min, and HR was measured every 1 min. SBP was higher in OB and DG compared with HW youth at rest (p < .001). Despite working at lower relative workloads compared with HW, the BP response was elevated during exercise in OB and DG. For similar HR and oxygen consumption rates, BP responses to exercise were slightly higher in OB and DG compared with HW. OB and DG youth both display elevated resting and exercise BP relative to HW peers. Obesity may play a greater role than dysglycemia in the exaggerated BP response to exercise in youth.

Vigorous Intervals and Hypoglycemia in Type 1 Diabetes: A Randomized Cross Over Trial

Adding vigorous-intensity intervals (VII) to moderate-intensity exercise prevents immediate declines in blood glucose in type 1 diabetes (T1D) however the intensity required to minimize post-exercise hypoglycemia is unknown. To examine this question, ten sedentary T1D individuals completed four treadmill exercise sessions: a control session of 45 minutes of walking at 45–55% of heart rate reserve (HRR) and three sessions consisting of 60 seconds (VII) at 70%, 80%, or 90% of HRR every 4 minutes during exercise at 45–55% of HRR. We used continuous glucose monitoring (CGM) to measure time ≤3.9 mmol/L, glucose variability, hypoglycemia frequency and area under the curve (AUC) for hypoglycemia and hyperglycemia for 12 hours post-exercise. We also examined growth hormone and cortisol responses during and following exercise. In the 12 hours post-exercise, the percentage of time ≤3.9 mmol/L, glucose variability, and AUC for hypoglycemia and hyperglycemia were similar across conditions. The frequency of hypoglycemic events was highest after the 90% intervals compared to the control arm (12 vs 3 events, p = 0.03). There was a trend towards elevated growth hormone with increasing exercise intensity but cortisol levels were similar across conditions. Adding VII to moderate intensity exercise may increase hypoglycemia risk at higher intensities.

The association between bouts of moderate to vigorous physical activity and patterns of sedentary behavior with frailty

Objectives To determine if bouts of moderate‐vigorous physical activity (MVPA) and patterns of sedentary behavior are associated with frailty. Method Accelerometry from community‐dwelling adults ≥50 years old (n = 2317) enrolled in the 2003–04 and 2005–06 National Health and Nutrition Examination Survey were used. Bouted (≥10 min) and sporadic (<10 min) durations of MVPA were analyzed based on meeting 0%, 1–49%, 50–99%, and ≥100% of physical activity guidelines (150 min/week of MVPA). Prolonged sedentary behavior were bouts lasting ≥30 min. Breaks from sedentary behavior were defined as any ≥1 min interruption in sedentary behavior. Average intensity (counts/min) and duration (minutes) during breaks were also analyzed. Frailty was measured with a 46‐item frailty index. Results Multivariable linear regression models adjusting for age, sex, education, ethnicity, income, marital status, smoking, alcohol consumption, body mass index, total sedentary time and accelerometer wear time indicated that meeting any percentage of the activity guidelines with bouted and sporadic MVPA was associated with reduced frailty. This relationship peaked at meeting 50–99% of guidelines and was associated with a 1.5 and 2.0 point reduction in the frailty index for bouted and sporadic MVPA, respectively. Two additional prolonged sedentary behavior bouts/day were associated with an additional frailty index deficit while every additional 100 cpm in average break intensity and every 2 min in average break duration were associated with one less deficit. Total sedentary breaks were not associated with frailty. Conclusion These population‐level data give justification for determining if interventions which target short bouts of MVPA and interrupting prolonged, uninterrupted time spent in sedentary behaviors can treat or prevent frailty worsening. HighlightsSporadic and bouts of MVPA were similarly associated with reductions in frailty.Small doses of sporadic or bouted MVPA resulted in significant frailty reductions.Breaking up long bouts of sedentary time was protective of frailty.The intensity and duration during breaks was more important than break frequency.

A systematic review of the association between sedentary behaviors with frailty

Objective: Lifestyle factors such as physical activity are known to reduce the risk of frailty. However, less is known about the frailty‐sedentary behavior relationship. A systematic review was conducted to synthesize the available evidence concerning associations between sedentary behaviors and frailty levels in adults. Method: MEDLINE, Embase, Web of Science, CINAHL, SPORTDiscus, Scopus, and the World Health Organization Clinical Trials Registry were searched up to August 2017 for observational studies in adults >18 years for cohort studies. Included studies identified frailty as a specified outcome using a multi‐component tool. Sedentary behavior was measured by self‐report or objectively. Studies with statistical models adjusting for at least one covariate were included. Meta‐analysis could not be performed due to the heterogeneity in frailty and sedentary behavior measures. Results: Six longitudinal and ten cross‐sectional studies were identified (n = 14, 693 unique participants); sample sizes ranged from 26 to 5871. Studies were generally at a low to moderate risk of bias. Most studies (n = 9) used the Fried criteria to measure frailty. Five studies measured sedentary behavior by questionnaire, with three studies specifically measuring television viewing time. Seven studies measured sedentary time by accelerometry. Thirteen of sixteen studies observed a detrimental association between high amounts of sedentary behaviors and an increased prevalence of frailty or higher frailty levels. Six of seven studies adjusting for physical activity behaviors demonstrated an independent association between sedentary behaviors and frailty. All six longitudinal studies found a negative association between sedentary behaviors and frailty. Conclusions: Sedentary behaviors were associated with a higher prevalence of frailty or higher frailty levels. Longitudinal studies are needed that adjust for physical activity when determining the association between sedentary behaviors and frailty. The efficacy of sedentary behavior reduction outside of physical activity interventions to treat and reverse frailty should also be tested.