The metabolic syndrome : does it exist in Africans in transition in the Northwest Province
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Background: The term 'metabolic syndrome' is used to describe the clustering in a person of risk factors 'which is associated with the chronic diseases of lifestyle. Considerable evidence exists that insulin resistance is the underlying common factor in the development of the metabolic syndrome. At present, urbanisation occurs very rapidly in the South African population. According to the literature urbanisation is accompanied by the adoption of Western lifestyles and dietary habits. Therefore, overnutrition, the prevalence of risk factors, morbidity and mortality from chronic diseases of lifestyle arc expected to increase among urbanising communities. Objectives: 1. The questions addressed were whether the metabolic syndrome exists in the African population of the Northwest province and if it does, what are the characteristics of this syndrome in this population? 2 The hypothesis tested in this study was that despite the concept of "healthy obesity" in black women (Walker et al.. 1991) the metabolic syndrome will also develop in black South Africans when they adopt Western lifestyles, Study design: This study was part of the larger THUSA-study. THUSA was a cross-sectional study of 1854 "apparently healthy" African men and women volunteers, recruited from 37 randomly selected sites in the Northwest province and stratified for age, gender and level of urbanisation. A sub-sample of all the fasted Subjects, 193 men and 233 women, between the ages of 15 and 65 years was selected to investigate the characteristics of the metabolic syndrome. Research methods: A variety of research techniques were used by a multidisciplinary team to collect the data. The results were statistically analysed by using the SPSS 9.0 programme, performing non-parametric statistical tests. Spearman's correlations were used to identify relationships between risk factors of chronic diseases of lifestyle and insulin sensitivity. The GLM Multivariate procedure was used to investigate interactions between risk markers for the chronic diseases of lifestyle and the insulin sensitivity index. Cross-tab statistics were used to calculate odds ratios. Logistic regression analyses were used to investigate the influence of lifestyle factors in the development of the metabolic syndrome. These relationships were used to investigate conditional probabilities in the predictive value of variables for early detection in the development of the metabolic syndrome. Results: The influence of urbanisation on this population was reflected in a deterioration in lipid profiles, an increased body mass index: (BMI) and percentage body fat (calculated from girths), increased iron status and an increase in insulin resistance. Although age was inversely associated with insulin sensitivity in the women, no linear association between insulin resistance and age was found. An increase in serum urea levels in women was associated with insulin resistance which should be further investigated as it may hold a key between kidney function and hypertension in African women. A progressive increase in the risk factors for type 2 diabetes (NIDDM), coronary heart disease (CHD) and obesity was detected in these subjects from a condition of high insulin sensitivity towards high insulin resistance. However, these risk factors were still within the boundaries of normal ranges (Chapter 6). Clusters of two and more (up to five in men and six in women) traditional risk factors for the metabolic syndrome were also found in these "apparently healthy" subjects. Clustering of two and more risk factors occurred in 25% of the men and in 32% of the women. These clusters of risk factors were found despite the absence of insulin resistance, although clusters of more than two risk factors occurred more frequently in the insulin resistant subjects. Serum total cholesterol seemed to be a predictor for the clustering of risk factors at levels higher than 4.4 mmol/L in men and 4.8 mmol/L in women. However, large confidence intervals were observed and results should be interpreted with care. Physical activity seemed to be protective against the clustering of risk factors in the women. Raised plasma fibrinogen levels seemed to be involved in the developing of insulin resistance in the women and in the clustering of risk factors in the men. High consumption of food energy seemed to be indicative of the development of insulin resistance in the women while in the men it seemed to be protective against the clustering of risk factors. This contradiction might be an indication of the importance of food composition rather than quantity in the development of the metabolic syndrome, or it could be related to the fact that "overnutrition" as indicated by a mean BMI of 26.9 kg/m2 was present in the women while "undernutrition" (mean BMI of 20.5 kg/m2) was more prevalent in the men. An increase in energy intake would represent further overnutrition in women while in men it would result in more adequate or optimal nutrition. Conclusions * Insulin resistance and the clustering of risk factors occurred in the study population. * Insulin resistance was not the underlying common factor in all the clusters of risk factors for the metabolic syndrome in these subjects. Therefore, the term "multiple metabolic syndrome” suggested by Liese et al (1998). will probably be more appropriate to use for this study population. * Obesity and an inactive lifestyle seem to be risk factors for the development of insulin resistance and a "multiple metabolic syndrome" in these women of the study population.
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