A thesis submitted for the degree of Doctor of Philosophy
Research Centre for Society and Health
Buckinghamshire New University
Background: The prevalence of overweight, obesity and obesity-related disease, mainly cardiovascular disease (CVD), is increasing in both developed and developing countries. Ethnic differences have been reported in the prevalence of overweight, obesity and CVD. However, measures used to define overweight and obesity, and identify increased risk of CVD were developed and validated in predominately Caucasian populations in developed countries. Consequently, these measures may not accurately define disease risk in all population groups. Therefore the specific aims of this programme of study were:
To establish the relationship between adiposity and cardiovascular risk factors in different ethnic groups.
To identify field measures of adiposity, relating to cardiovascular risk in different ethnic groups.
To compare the relationship of adiposity and cardiovascular risk factors in a single ethnic group, that of a rural and an urban population in Zimbabwe.
To identify risk factors for CVD related to adiposity in a population of African origin.
Three empirical studies were undertaken. In study one, 312 adult subjects from three ethnic groups (Afro-Caribbean (n=106), Caucasian (n=165) and South Asian (n=41)) were recruited from a University. Twenty-six (26) of each group were individually matched for age (±3 years) gender and BMI (±2 kg/m2) to allow for comparability. Measures of body composition included height, weight, waist and hip circumferences, skinfold thickness measures, body density and percentagebody fat.
In study two, 81 subjects from two ethnic groups (Afro-Caribbean (n=39) and Caucasian (n=42)) were recruited and tested. They were matched for age, gender and BMI using the same criteria as study one. In addition to the body composition measures taken in study one, random non-fasting blood glucose, total cholesterol, triglycerides and blood pressure were taken.
In study three, 55 men and 108 women from rural Zimbabwe, 8 men and 17 women from an urban low-density suburb in Harare Zimbabwe, and 28 male and 16 female students from the University of Zimbabwe were recruited and tested. In addition to all measures of body composition in studies one and metabolic analysis in study two, participants’ dietary intake was assessed by food frequency questionnaire and 24hour recall and physical activity was assessed by a physical activity questionnaire.
The relationship between BMI and %BF was not the same in all ethnic groups. (aim 1)
There were ethnic differences in the cardiovascular risk predictors between Afro-Caribbean and Caucasian men and women. (aim 1)
It is not recommended that BIA is used as a substitute for TBW estimation in multi-compartment models. (aim 2)
In three groups of Zimbabweans from urban, rural and university locations, a pattern emerged. Amongst women, urban women were at greatest risk, reporting highest values for all variables, followed by rural then university women. Amongst men, urban men were at highest risk, however there were few differences between rural and university men. (aim 3).
Finally, increased WC and dyslipidemia are associated with increasing BMI in populations of African origin. (aim 4)
The relationships between overweight, obesity and risk of obesity-related disease differ between different ethnic groups. Moreover, in the groups from Zimbabwe, differences in obesity-related risk were associated with being female and living in urban areas. Therefore, application of universal measures for defining obesity and related diseases may not be applicable to all ethnic groups.
I am eternally indebted to my supervisors Professor David Brodie and Dr Joan Gandy for their tireless efforts, patience, knowledge and guidance throughout these years.
I am grateful for the advice and guidance I received from the late Professor Lucie Malaba and colleagues at the University of Zimbabwe.
To Dr Paul Amuna and Dr Francis Zotor at the University of Greenwich who assisted with software for dietary analysis.
Many thanks to Fortune Maduma, Lydia Muzangwa, Mthulisi Dube, and Cynthia Matare who assisted me with data collection in Zimbabwe.
I am grateful to Paul Sharp from Point of Care Services for his ingenious idea for a battery charger which was invaluable in my fieldwork in rural Zimbabwe.
To Dumisani Nyoni, Mrs Sithembiso Nyoni and staff members of ORAP Zimbabwe who assisted with accommodation and transportation during the fieldwork in rural Nkayi, Zimbabwe.
To all those who participated in the studies in the UK and Zimbabwe.
To my friends who’ve provided useful diversion at times of high stress
To Dr David Shaw for his moral support throughout the years
To my family, especially my uncle Kidwell and Aunt Ann and my cousins who have been very supportive.
To my sister, Sibonile for her support
Finally and most importantly, I am especially grateful to my mother, Reginah Mathe, for her unconditional support, encouragement and love, without which none of this would have been possible.
I dedicate this thesis to my father Fortune Mathe, who is missed dearly.
I take responsibility for all the material contained within this thesis and confirm this is my own work.
This thesis has been supplied on condition that anyone who consults it is understood to recognise that its copyright rests with the author under terms of the United Kingdom Copyright Acts. No quotation from this thesis and no information from it may be published without proper acknowledgement.