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Cardiovascular disease risk in children : 'pre-clinical' markers and the impact of body composition, physical activity and cardiorespiratory fitness

Henaghan, J (2008) Cardiovascular disease risk in children : 'pre-clinical' markers and the impact of body composition, physical activity and cardiorespiratory fitness. Doctoral thesis, Liverpool John Moores University.

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Cardiovascular disease is one of the largest killers in the UK representing 30% of all global deaths. The underlying processes of the disease are thought to begin in childhood. Whilst traditional risk factors of CV disease (e.g. hypertension, hyperlipidemia, obesity, smoking, stress and sedentary lifestyles) are becoming increasingly prevalent within the younger generation there remains the need for the establishment of earlier or "pre-clinical" markers of future CV disease risk or current atherosclerotic load such as left ventricular (LV) mass, diastolic function and carotid intima-media thickness( cIMT). Further, assessing the association of these markers to other risk factors and then determining the impact of physical activity (PA) interventions is warranted. Initially we assessed the impact of body composition, PA and cardiorespiratory (CR) fitness upon left ventricular LV mass, carotid-intima media thickness (cIMT) and LV diastolic function in 218 9-11 year old primary schoolchildren. Pubertal status was assessed through a maturity offset calculation. LV mass, cIMT, and LV diastolic function were assessed via ultrasound. Body mass index was assessed via anthropometry whilst fat mass [FM] and lean mass [LM] were determined via dual X-ray absorptiometry. Average 3-day PA was recorded via a uni-axial accelerometer and CR (VO?peak) was determined from a graded treadmill test. Relationships were analysed using bivariate correlations and forced entry multiple regression. All children were classified as being below their peak height velocity. Together LM, FM, sex and moderate to vigorous (MV)PA accounted for 59% of the variance in LV mass with LM being the most important predictor (P<0.005). Sex, LM, FM and VO?peak explained only 19% variance in cIMT and just 9% of the variance in LV diastolic function was accounted for by LM, FM blood pressure and sex. Data for MVPA had no significant relationship to any cardiovascular (CV) variables although was negatively correlated with FM. The strong association between LV mass and body composition likely represents normal growth. The limited shared variance between predictor variables and cIMT and LV diastolic function suggests that those pre-peak height velocity children in the current cohort who were overweight, inactive and unfit were not yet at an increased CV disease risk. Thus there is a window of opportunity for intervention programmes to be implemented that reduce CV disease risk before adolescence and adulthood. Following this, an exploratory trial was conducted to introduce the use of PA interventions in pre-pubertal children. Sixty-one 10-11 year old Liverpool primary school children volunteered and were randomly assigned by school to a STEX programme (2 x 60 min sessions per week at a heart rate of ~145 beats min??), a PASS programme (weekly physical activity tasks and pedometer challenges) and a control (CON; no intervention). Pre-clinical CV measures and body composition were measured before and after the 9-week intervention period. The primary outcome variable was cIMT, with LV mass, LV diastolic function, and body composition defined as secondary outcomes. Delta (?) scores were analysed by ANCOVA, with baseline scores as the covariate. For the primary outcome, the probability that the population effect of the intervention is at least as great as the pre-specified minimum clinically importance difference (MCID) was estimated, to evaluate clinical relevance. All participants met 75% compliance criteria for STEX and PASS. The effect of the STEX intervention (compared with CON) was a mean benefit of -0.018mm for average maximum cIMT (90% CI, -0.039 to 0.002mm), and -0.016mm for average mean cIMT (90 % CI, -0.040 to 0.008mm). The probability (% chances) that the true population effect of the STEX intervention would be clinically beneficial was 79% for average maximum and 71% for average mean cIMT. The PASS intervention did not result in clinically important effects, and no other substantial changes were observed for the secondary outcome variables. The relatively high probability of clinically beneficial effects of the STEX intervention suggests that a larger, "definitive" randomised trial with longer follow-up is warranted to define the effectiveness of the intervention more precisely. As a consequence the longer PA intervention study observed 152 children aged 9 to 10 years over 12 months. All of the echocardiographic, body composition, CR fitness and PA variables mentioned were assessed as previously discussed. Children were randomly assigned by school to an intervention group. Control (no intervention), PASS (as before except delivered during school hours to enhance compliance), high intensity physical activity (the same as STEX but renamed due to the addition of another structured exercise group) or fundamental movement skill ([FMS] 2x 60 min sessions per week of skill based activities). These interventions took place over a year period with participants being assessed at baseline, approximately mid-way through and post-test (52 weeks). Initial factorial ANOVA analysis comparing all 3 intervention groups and a control group before, during and after the 12 month intervention period, found limited statistically significant evidence for a positive impact of PA interventions compared to controls in pre-pubertal children. However, after adjusting for confounding variables in an ANCOVA analysis some sporadic benefits of PA interventions on CV variables were uncovered. An increase in LV mass over 12 months, after adjustment, was lower in the HIPA group compared to CON group (11.5 g; 90% CI, 2.0 to 21.0 g). This change was also lower in the FMS group compared to CON group (13.8 g; 90% CI, 4.6 to 23.1 g). The ANCOVA adjusted change scores for both mean and max cIMT were less in the intervention groups compared to CON group but only in the PASS group were these differences significant (P<0.05). PASS increased its mean cIMT (-0.014mm less than control (90% CI, -0.002 to -0.030)). Somewhat surprisingly the intervention programmes had no positive effect on CR fitness (indeed this decreased), PA measures and/or body composition over and above changes observed due to growth. This thesis has provided a unique insight into the 'pre-clinical' CV disease risk factors in pre-pubertal children and the impact of differing PA activity interventions with this group. Interestingly the research has shown that within this population overweight/obese, inactive low CR fit individuals are generally not at a higher CV disease risk than their aged matched 'healthier' counterparts. When PA interventions are introduced in the short term positive changes in cIMT were seen, however, this is not reciprocated in longer PA interventions possibly due to a larger maturation effect over 12 months. Interestingly year long interventions provide some attenuation of growth-related changes in CV disease risk factors but these changes are generally small and sporadic. It is suggested that further research over a longer period of time with more 'at risk' populations is needed. The PA interventions adopted achieved high attendance and compliance records and thus may be transferable out of the research process. It is interesting to also speculate that future research may not need to administer high impact activity, as previously thought, as some positive data was obtained in more general lifestyle interventions involving more knowledge transfer.

Item Type: Thesis (Doctoral)
Subjects: R Medicine > RC Internal medicine > RC1200 Sports Medicine
R Medicine > RJ Pediatrics > RJ101 Child Health. Child health services
Divisions: Sport & Exercise Sciences
Date Deposited: 13 Mar 2017 11:54
Last Modified: 13 Mar 2017 11:54
URI: http://researchonline.ljmu.ac.uk/id/eprint/5901

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