Association between body fat composition and blood pressure level among secondary school adolescents in Dar es Salaam

Abstract

Background: Excess body fat and high blood pressure are important risk factors for increased cardiovascular morbidity and mortality, and both may have their roots of occurrence in childhood and during adolescence. However, less is known about the association between body fat composition and blood pressure levels among Tanzanian adolescents. Aim: To study the association between body fat composition and blood pressure levels among secondary school adolescents in Dar es Salaam. Methods: A total of 582 (52.1% males and 47.9% females) adolescents from 5 secondary schools within Dar es Salaam region were selected using systematic random sampling method. A structured questionnaire was used to collect information on demographic characteristics as well as other cardiovascular risk factors. Blood pressure, height, weight, waist circumference and hip circumference were measured following standard methods. Body fat composition was assessed using skinfold thickness method and individuals were categorized as under fat, healthy, over fat or obese according to World Health Organization cut off points for adolescents. Systolic and diastolic hypertension was defined as ≥90th percentile for age, height and gender of the adolescent. Data management and analysis was performed using SPSS software, version 20. A p-value of <0.05 was considered to indicate a significant statistical difference. Results: The mean ±SD age of the total population was 16.5±1.8 years, with boys being slightly but significantly older than girls (16.9± 1.7 versus 16.2 ± 1.9 years, p<0.001). The proportion of adolescents with overweight or obesity by body mass index (BMI) categorization was found to be 17.4% while over fat or obesity by fat percentage categorization was present in 22.2% of the total population studied. Girls had significantly higher proportion of overweight both categories when compared to boys being 10.5% versus 6.9% for BMI and 15.6% and 6.5% for fat percentage respectively, all p< 0.001. The mean ±SD systolic and diastolic blood pressure of the total population was 120±11 and 69± 8 mmHg respectively. The proportions of adolescents with systolic, diastolic and combined hypertension in the total population were 17.5%, 5.5%, and 4.0% respectively. In the total population both mean systolic and diastolic blood pressure positively and significantly correlated with BMI (r = 0.24 for SBP and 0.24 for DBP) and with waist circumference (r = 0.18 for SBP and 0.22 for DBP), all p<0.05. Furthermore, in the total population the mean diastolic blood pressure also had a positive and significant correlation with mean body fat percentage (r = 0.25, p<0.001), while this was not the case for mean systolic blood pressure (r = -0.02, p = 0.56). Analyses done separately for boys and girls showed that boys had same findings as those obtained in the total population, while girls had in addition a significant positive correlation between mean systolic blood pressure and mean body fat percentage (r = 0.18, p < 0.05). Conclusion and recommendations: A high proportion of adolescents with elevated BP was seen among those with elevated BMI values (overweight and obesity) compared to those with normal BMI, girls being significantly more hypertensive and obese than boys. BMI predicted blood pressure level better in this population compared to body fat percentage method. We recommend further studies to assess efficacy of skinfold thickness method in other populations in predicting blood pressure level. Also educational programs on modifiable risk factors particularly promoting weight loss may help prevent high blood pressure in adolescents. and obesity by