Relationships between physical activity status, intima-media thickness and cardio-metabolic risk factors in a cohort of teachers: the SABPA-study

PhD (Human Movement Science), North-West University, Potchefstroom CampusPhysical inactivity is a significant health concern, contributing to the development of non-communicable diseases (NCDs) in the 21st century. Among NCDs, cardiovascular diseases (CVDs) are major contributors to the high mortality rate, therefore early detection of CVDs is needed. Carotid intima-media thickness (CIMT) is a non-invasive measure used to evaluate the progression of atherosclerosis, an underlying cause of CVD. However, limited research is available regarding the relationship between physical activity (PA), cardio-metabolic risk factors and CIMT in teachers. The main aim of this thesis was to determine the relationships between objectively measured PA status, cardio-metabolic risk factors and CIMT. A cross-sectional study design using secondary data from the Sympathetic Activity and Ambulatory Blood Pressure in Africans (SABPA) prospective cohort study on a total of 216 teachers drawn from Dr Kenneth Kaunda District, North West Province, South Africa was employed. Only participants with 7-day ActiHeart PA data were included in the study. Cardio-metabolic risk factors were objectively measured; whereas, alcohol usage and smoking were subjectively assessed. Height (cm), mass/weight (kg) and biochemical values were determined following standard procedures. Also, sphygmomanometer and 24-hour ambulatory blood pressure recordings were used to measure resting blood pressure. SonoSite Micromaxx ultrasound was used to measure CIMT. Participants were classified as presenting with or without cardio-metabolic syndrome according to the Joint Interim Statement. Data were analysed using the Statistical Package for Social Sciences (SPSS) version 26. Descriptive statistics (mean±standard deviations) as well as frequencies were calculated. Partial correlations were determined to identify the relationship between the variables. The level of significance was set at p ≤ 0.05. The results of this study indicated that 67% of the participants were sedentary and 33% participated in light-intensity PA. Male teachers had significantly higher mean CIMT values than their female counterparts (p < 0.05). An inconclusive weak borderline negative association between CIMT and mean 7-day awake metabolic equivalent of task (METs) (r = -0.19; p = 0.08) was found, and CIMT was moderate inversely associated with total energy expenditure (r = -0.31; p = 0.05) in sedentary male teachers. In the measures of body composition, waist circumference (WC) was positively and significantly (β = 0.151, p = 0.027) related to CIMT. A significant positive relationship was observed between WC and CIMT. The observed correlation was explained by 2.3% (R2; 0.023) WC in the model, and it was an inconclusive borderline statistically significant (F(2; 211) = 2.489; p = 0.085) result. The addition of PA into the regression models did not change the magnitude of the regression coefficients for any of the body composition variables and CIMT. Twenty-nine percent of the teachers were classified with cardio-metabolic syndrome. A weak significant positive relationship between WC and triglycerides in the entire group of teachers (r = 0.16; p = 0.02) was present. A weak significant negative relationship was found between mean 7-day awake METs and triglycerides (r = -0.29; p = 0.02), with an inconclusive borderline negative association between gamma-glutamyl transferase (GGT) and mean 7-day awake METs (r = -0.25; p = 0.06); activity energy expenditure (r = - 0.24; p = 0.06); and physical activity level (r = -0.23; p = 0.07). After adjustments for age group, self-reported smoking and alcohol use, a weak significant negative relationship between mean 7-day awake METs and triglycerides (r = -0.28; p < 0.01) remained with small changes. The conclusion drawn from this study though not conclusive highlighted that participation in light PA was associated with lower CIMT, especially in female teachers. In addition, CIMT was positively associated with WC. The high cardiovascular risk profile (increased C-reactive protein, high overweight/obesity prevalence) diminished the protective role of PA in the relationship between obesity and CIMT. Physical activity is negatively associated with GGT and triglycerides in teachers with cardio-metabolic syndrome. Physical activity intervention studies are recommended to determine effective interventions to provide information on how to limit the development of atherosclerosis.Doctora