The risk of metabolic syndrome as a result of lifestyle among Ellisras rural young adults : Ellisras longitudinal study

Thesis (M. Sc. (Physiology)) --University of Limpopo, 2019

Introduction: There is an increased trend in the prevalence of hypertension in children and adolescents in African countries. There are complications in diagnosing hypertension in children and adolescents due to the variation of blood pressure (BP) values with age, gender and height. The progression of the health transition with non-communicable diseases (NCDs) adds significantly to the disease burden, despite infectious diseases and undernutrition remaining persistent in both low and middle-income countries. Metabolic syndrome (MetS) is a global problem associated with the clustering of several cardiovascular risk factors. South African evidence suggests an upsurge of NCDs amidst the existence of communicable diseases (CDs) such as HIV/AIDS and tuberculosis. Moreover, NCDs and CDs in the country are influenced by socio-demographic factors; and thus tend to be more prominent in certain segments of the population. Aim and Objectives: The aim of this study was to perform blood pressure to height ratio and to determine lifestyle risk factors associated with metabolic syndrome among the Ellisras rural population aged 6-30 years, who are part of the ELS. Methods and materials: The current study is based on secondary data analysis of the Ellisras Longitudinal Study (ELS) and was conducted in two phases. Phase 1 included data analysis of all the participants in the ELS. This sample included a total number of 9002 children and adolescents (4678 boys and 4324 girls), aged 6-17 years. Parents or guardians provided written informed consent. Phase 2 consisted of biochemical analysis from a subsample of participants in the ELS. The subsample included 624 participants (306 males and 318 females) aged 18-30 years at the time the study was conducted. All participants underwent a series of anthropometric measurements (waist circumference and height) according to the standard of the International Society for the Advancement of Kinanthropometry (ISAK). The waist circumference (WC) measurements were taken to the nearest 0.1 cm, using a soft measuring tape. Metabolic syndrome was defined according to the International Diabetes Federation (IDF) criteria. Metabolic syndrome risk factors included total cholesterol (TCHOL), triglycerides (TG), high-density lipoprotein cholesterol (HDLC), elevated fasting blood glucose (FBG), elevated blood pressure (BP) and high waist circumference (WC). A dietary intake questionnaire was also administered to each participant and self‑administered questionnaire was used to collect data on lifestyle factors, including smoking and alcohol intake. Dietary intake variables used in the linear regression method were log transformed prior to analysis because of their skewed distribution. Receiver-operating characteristic (ROC) curve was used to assess the accuracy of BPHR to screen children with prehypertension and hypertension. The optimal systolic BPHR (SBPHR) and diastolic BPHR (DBPHR) cut-off points for hypertension were determined. Sensitivity/specificity, positive predictive values and negative predictive values were calculated. Results: The optimal thresholds for defining prehypertension was 0.77 in children aged 6-10 years and 0.73 in adolescents aged between 11 and 17 years for systolic BPHR and 0.55 in children and 0.53 in adolescents for diastolic BPHR, respectively. The corresponding values for hypertension stage 1 were 0.76 and 0.73 for SBPHR and 0.50 and 0.58 for DBPHR, respectively. The BPHR is an accurate tool for screening elevated BP in Ellisras children aged 6-17 years. This can help to prevent the misclassification of children and adolescent hypertension. Furthermore, this tool can be used to screen children before the development of prehypertension and hypertension. Moreover, it can be used to manage hypertension in Ellisras children, ultimately reducing the risks of developing hypertension and associated cardiovascular disease in adulthood. Overall, the prevalence of metS was 23.1% (8.6% males and 36.8% females). Females appeared to have higher mean values for WC, FBG, TCHOL and LDL-C than males (82.14, 5.62, 4.62 and 2.97, respectively). The only significant gender difference observed was on WC (p<0.001). Males on the other hand had higher mean values for HDL-C, TG, SBP and DBP than females (1.20, 1.06, 125.91 and 71.44, respectively). The only significant difference observed in this case was on SBP (p<0.001). No significant age group differences were observed in all the metabolic risk factors with the exception of DBP where the older (25-30 years) participants presented with high SBP than the younger age group (18-24 years) (70.96 mmHg vs 68.78 mmHg, p<0.05). While, majority of females had significantly high WC, elevated total cholesterol and LDL-C, and reduced HDL-C; majority of males had elevated BP, SBP and DBP. No significant age and gender differences were observed on dietary intake. However, according to the linear regression analysis, no association between log total energy, log added sugar, log SFA and log MUFA with metabolic risk factors. There was a low and negative significant association between log fibre with SBP and DBP (β:-0.004, p=0.003 and β:-0.004, p=0.046), respectively, crude. After adjusting for the potential confounding factors, log fibre was also associated with FBG (β:-0.028, p=0.046). Log PUFAs was inversely associated with FBG, HDL-C and SBP crude. Log trans fatty acids was inversely associated with WC, HDL-C and SBP crude. Both log PUFAs and log trans fatty acids were not associated with any metabolic risk factors after adjusting for potential cofounding factors. Log protein was inversely associated with SBP both crude and adjusted for potential cofounding factors. On predicting the actual risk using the logistic regression analysis, participants who had high dietary energy intake were significantly less likely to present with larger WC, low HDL-C and high LDL-C (OR: 0.250 95%CI [0.161;0.389], OR: 0.306 95%CI [0.220;0.425] and OR: 0.583 95%CI [0.418;0.812], respectively), but more likely to presents with elevated FBG, high TCHOL, high TG and hypertension (OR: 1.01 95%CI [0.735;1.386], OR: 1.039 95%CI [0.575;1.337], OR: 1.186 95%CI [0.695;2.023], OR: 5.205 95%CI [3.156;8.585], respectively) crude. After adjusting for age, gender, smoking and alcohol status, high energy intake was more likely to increase two times high the large WC and elevated FBG among study participants (OR: 2.766 95%CI [0.863;3.477] and OR: 2.227 95%CI [1.051;3.328], respectively). Furthermore, low dietary fibre intake was nearly four times more likely to increase the low HDL-C, crude (OR: 3.864 95%CI [1.067;13.988]) crude. Those participants who consumed high trans fats were more likely to present with high FBG (OR:1.424 95%CI [0.985;2.060]), but less likely to present with LDL-C (OR: 0.540 95%CI [0.321;0.906]) crude. However, after adding potential cofounding factors, participants with high fatty acid were less likely to present with high FBG (OR: 0.672 95%CI [0.441;1.023]). Conclusions: MetS is prevalent in young adults in Ellisras and is differentiated by age and gender with more females at an increased rate by virtue of their body size status, reduced HDL-C, elevated FBG and high LDL-C and the diet they consume that is in most cases high energy, more carbohydrates, high added sugar and SFA. Therefore, identifying groups that are at an increased risk and those that are in their early stages of MetS will help improve and prevent the increase of the metS in the future. These results have high policy implications. KEY CONCEPTS Metabolic syndrome; risk factors; blood pressure; blood pressure to height ratio; cardiovascular disease; dietary intake; rural South African.