Abstract.
The aim of the study was to determine differences in cardiovascular disease (CDV) risk factors in four cross-tabulated sets of body fatness and cardio respiratory fitness in adolescents. The participants included 755 females and 860 males aged 9-15 years from schools in Australia. Subjects were cross tabulated using maximum oxygen consumption and percentage body fat to split the groups to four .In males, differences across the group included blood pressure, triglycerides, high and low density lipid cholesterol but in females the variations were observed in high density lipid cholesterol and blood pressure .In females, variations were seen between high-fat/high-fitness group and high-fat/low-fitness categories, for all measures of blood pressure. According to Eisenmann (2007), an overall trend of low blood pressure values in the low fat group for both genders was noted compared to the high fat counterparts .A similar trend was observed in males blood lipids analysis results .A linear relationship in CVD risk score across the subgroups was noted in both genders. The above results provide grounds for consideration of fitness and fatness when CVD risk factors are being interpreted in high-fat youth.
Introduction.
Over the recent past, it has been noted that cardiovascular disease morbidity and mortality is associated with overweight in adults however, this relationship between cardiovascular disease and overweight has been modified by cardio respiratory fitness. Consistent studies by Blair and colleagues indicate that health effects of high body fat levels in adults can be reduced by cardio respiratory fitness. Due to the current concerns in over weight youths on pediatric obesity epidemic and for cardio vascular disease, a fat -but-fit hypothesis was examined in adolescence youths. Results from both studies show that within both high and low body mass index brackets, a greater level of cardio respiratory fitness was linked to cardio vascular disease risks. According to Eisenmann (2007), this study also aided to explore further the hypothesis by use of health related indicators in a large sample of youths from the Australian fitness health survey. It’s hypothesized that high cardio respiratory fitness level would influence positively the cardio vascular disease within the fatness group set. The main aim of this study was to investigate variations in cardio vascular disease risk factors across four groups of body fat and cardio respiratory fitness.
Methodology.
According to Coonan guidelines (1983), this study was performed using a specific protocol. Information obtained included a secondary analysis of Australian fitness and health survey data (AHFS). This data by AHFS was obtained from a cross sectional study of a population of around 8500 school children aged 7-15 years that were sampled from 109 schools which had health – related and fitness behaviors reported.
The design of this survey was a two -staged probability setup, with the first stage involving careful selection of schools and stage two consisting of random sampling of males and females from each year of age in the total schools enrolled. School wasn’t taken into account as a clustering factor reason being, the sampling procedure (both five males and females from each school) and the large number of schools (clustering units) relative to size of the sample reduced the impact of clustering.
According to Andersen (1993), the participating pupils were categorized into four groups using maximum estimate of oxygen consumption (VO2max) and body fat percentage to divide the groups. Cardiovascular disease risks factors considered were; triglyceride, both high and low density lipoprotein cholesterol, fasting total cholesterol and blood pressure. Body fatness was measured by standard procedures using Holtain calipers at five different spots on the body’s right side. Calculation of percentage body fat was done using slaughter equations from sub capsular sites and triceps .According to Cureton (1994), a 1.6 Km run was used to determine Cardio respiratory fitness and thus used to calculate estimated oxygen consumption using the Cureton et al equation. For CDV risk factors, blood pressure (both the diastole and systole blood pressure) was measured in a seated position for a period of 5 minutes of rest using a mercury sphygmomanometer .Total cholesterol, triglycerides and high density lipoprotein cholesterol were determined using automated techniques at Flinders clinical center .The cardiovascular risk score was determined by first standardizing the individual risk variables for age. This was done by regressing them to take into consideration any non-linearity difference related to age and then adding the age standardized residuals for MAP, WC, TG and HDL-C. -1 was multiplied to the standardized HDL-C since its relationship with metabolic risks is inverse. These variables were picked because they represent same variables used in clinical criteria for adults for metabolic syndrome. A high score showed a lower favorable metabolic profile.
The study was passed by the committee of local ethics. A written parental consent and a child assent were required before participation in the study. The rest of the protocol was in accordance to the Helsinki outline. The analysis was confined in the age brackets since insufficient funds prevented performing costly procedures. Particular ages were chosen to represent pre, peri, and post pubertal stages.
Statistical data analysis.
Both estimated percentage fat and VO2max were used to categorize the subjects into four tabulated groups on the basis cut point of the fitness gram for VO2max (35mL.Kg-1min-1 for males and 42 35mL.Kg-1min-1 for males) and percentage fat (32% for females and 25% for males).According to Eisenmann (2007), this mode of classification resulted in high portion of subject being categorized into high fit /low fat group. Because of inadequate size of sample per stratum, adjustment of the cut points was done to correspond to 75 and 25 percentiles for percentage fat and VO2max respectively.
Variations across the set for CDV risk factors variables were determined by ANCOVA (analysis of covariance) while CDV risk score was assessed by ANAOVA. According to Bonferroni (1979), post hoc data was analyzed using Bonferroni multiple comparison test. SPSS package was used to execute all the analyses.
Results.
In males, differences across the group included blood pressure, triglycerides, high and low density lipid cholesterol but in females, the variations were observed in high density lipid cholesterol and blood pressure .In females’, variations were seen between high-fat/high-fitness group and high-fat/low-fitness categories for all measures of blood pressure. There was significance trend in the groups for both genders (F=60.6, P<0.001 in males and F=57.3, P<0.001 in females) .An overall trend of low blood pressure values in the low fat group for both genders was noted, compared to the high fat counterparts .A similar trend was observed in males in blood lipids results .A linear relationship in CVD risk score across the subgroups was noted in both genders. In both genders the high-fat/low-fit group had the leading composite risks scores (2.22 and 2.23) respectively which indicated a poorer CVD risk profile with the lowest score being in low-fat/high-fitness group, which represented the best metabolic profile .The below graphs show CVD risk score results.
Discussion.
Even thou the primary strategy of using FITNESSGRAM cut points gave insufficient sample sizes per strata, the calculated cut points are realistic on the basis of normal gender and age associated to variations in VO2max and percentage fat. They clearly indicate that adolescents and children with a higher body fat percentage and cardio respiratory fitness have their CDV risk factor being better than their high fat /low fit friends. According to Mark (2012), this shielding effect of fitness in increased fatness has been manifested well in adults (35), but now it has been shown to manifest in three children and adolescent samples from different countries using various methodologies for cardio respiratory fitness and fatness .This study has crucial implications in explaining the implications of pediatric obesity and even understanding type 2 diabetes, metabolic syndrome and Cardio vascular disease. Because overweight is linked with elevated risks in metabolic syndrome, our discovery that attenuation of CVD risk score is by fitness in high body fat group has brought important significance in treatment of obesity and prevention of metabolic syndrome in adolescents.
In his study, Coonnan (1983), noted that composite metabolic syndrome score derivation, gives a way of expressing the grouping adult metabolic syndrome components which is more sensitive to statistics and less prone to errors. The obtained results indicate variations in CDV risks in relation to gender, like in lipid classes. The gender specific variation reasons are quite unclear however, it can be speculated that interaction of fitness and fatness influences this factors differently in both females and males.
Problems.
Conclusion.
The above results give evidence for putting into consideration fitness and body fatness when analyzing CDV risk factors especially in high body fat youths.
References.
C E Barlow, H. W. (2005). Physical fitness, mortality and obesity. International Journal of Obesity , 121.
Eissenmann, J. ,. (2007). Fatness, Fitness & CVD Risk Factors in Children & Adolescents. . Medicine and Science in Sports & Exercise , 1251-1256.
L B Andersen, J. H. (2013). Tracking of cardiovascular disease risk factors including physical activity and maximum oxygen uptake from late teenage to adulthood. An 8-year old follow-up study. Journal of Internal Medicine , 130.
