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Biological risk factors for non-communicable diseases in Vietnam

Tran, NTT 2020 , 'Biological risk factors for non-communicable diseases in Vietnam', PhD thesis, University of Tasmania.

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Background and aims
The contribution of non-communicable disease (NCD) to total morbidity and mortality has risen over recent decades in Vietnam to reach around 63% of all deaths in 2016. This increase may be due in part to improved reporting but ageing of the population and increased exposure to NCD risk factors in a country undergoing rapid urbanisation/industrialisation is likely to be a contributing factor. Recent studies have demonstrated that NCDs are largely attributable to modifiable risk factors including physical inactivity, tobacco use, harmful drinking, and unhealthy diets. These risk factors can lead to elevations in overweight and obesity, blood pressure (BP), total cholesterol (TC) and blood glucose (BG). The World Health Organization (WHO) has recommended that priority be given to monitoring population levels of and changes in those four pathophysiological indicators as part of a comprehensive strategy to reduce NCD morbidity and mortality. To date, studies of NCD risk factors in Vietnam have largely been limited to the urban and affluent cities of Ha Noi, Ho Chi Minh and Can Tho. Our analyses of a nationally-representative population-based survey focus on the relationships of overweight and obesity, raised BP, elevated BG and raised TC with each other and with relevant socio-demographical and lifestyle factors. A particular focus was to investigate sex-differences in the mean levels or prevalence of NCD risk factors and their relationships with predisposing factors.
The survey participants aged 25−64 years (n=14,706, response proportion 64.1%) were selected by multi-stage stratified cluster sampling from eight provinces each representative of one of the eight geographical regions of Viet Nam. Sampling was undertaken, and measurements were made, in accordance with the STEPS survey methodology of the WHO. National estimates of overweight and obesity, raised blood pressure, elevated blood glucose and raised total cholesterol and their inter-relationships and associations with predisposing factors are presented in four studies.
Study 1 evaluates the separate and relative importance of waist circumference (WC) and body mass index (BMI) in cross-sectional relationships with BP, BG and TC. The measurements of WC and BMI were highly correlated (men r=0.80, women r=0.77) with lesser but statistically significant correlations also with BP, BG and TC. For men, the strongest and predominant associations with BP, glucose, and TC were for WC or an index based on WC. For women, this was true for BG, but BMI was more important for BP and TC. WC or an index based on WC provided better discrimination than BMI of hypertension and elevated BG, and of raised TC for men. Information on four new anthropometric indices – Body Adiposity Index (BAI), Abdominal Volume Index (AVI), Conicity Index (CI), and A Body Shape Index (ABSI) – did not improve model fit or subject discrimination.
Study 2 examines the potential misclassification of BP when only a single measurement is used. For systolic BP, 62.7% of participants had a higher first reading whilst 30.0% had a lower first reading, and 27.3% had a reduction of at least 5mmHg whilst 9.6% had an increase of at least 5mmHg. Irrespective of direction of change, increased variability in BP was associated with greater age, urban living, greater body size and fatness, reduced physical activity levels, elevated BG, and raised TC. As a consequence of reading-to-reading variability in BP measurements, almost 20% of subjects would receive a different diagnosis of hypertension based on the mean of two readings than they would when the diagnosis is based on a single reading. The results of this study do not generalise to the international protocols which recommend taking at least two BP measurements on two visits, but they do shed light on the consequences of taking a single reading with an automatic BP monitor and indirectly on the practice of taking a single reading with a sphygmomanometer.
Study 3 examined the relationship of systolic BP and BG with measures of obesity and central fat distribution and other factors whilst taking account of the inter-dependence between systolic BP and BG. Structural modelling identified direct effects for BG (men P=0.000, women P=0.029), age (men P=0.000, women P=0.000) and BMI (men P=0.000, women P=0.000) in the estimation of systolic BP, and for systolic BP (men P=0.036, women P=0.000) and WC (men P=0.032, women P=0.009) in the estimation of BG. There were indirect effects of age, cholesterol, physical activity and tobacco smoking via their influence on WC and BMI. The errors in estimation of systolic BP and BG were correlated (men P=0.000, women P=0.004), the stability indices (men 0.466, women 0.495) showed the non-recursive models were stable, and the proportion of variance explained was mid-range (men 0.553, women 0.579).
Study 4 investigates whether there is evidence of higher female-than-male mean levels of TC in Vietnam and, if so, whether it can be explained by ageing, by overweight and obesity, or by socio-demographic characteristics and behavioural factors. Men and women had similar mean levels of BMI, and men had modestly higher mean levels of WC, in each 5-year age category.
Whilst the mean TC of men increased with age until age 56 years, the mean TC of women increased more of less continuously across the age range but with a step-up at age 50 years to reach higher concentrations in a reversal of the male-female difference at lesser ages. The estimated step-up was not eliminated by adjustment for anthropometric indices including BMI or WC, or by adjustment for socio-demographic characteristics or behavioural factors. The estimated step-up was least for women with greatest weight.
The results of this research have important implications for the prevention and management of chronic disease in Vietnam and for the health system of the country. This project has produced novel population-based findings that suggest a causal role for overweight and obesity in BP variability, and demonstrated the appropriateness and benefits of adopting international protocols in the measurement of BP. The findings verify the need to measure both WC and BMI when monitoring prevalence of, and trends in, overweight and obesity. They are consistent with overweight and obesity playing a primary aetiological role in elevations of BP, BG and TC that are precursors to chronic disease. Additionally, by providing statistical evidence of a feedback loop between raised BP and elevated BG, there is new understanding of the contribution that overweight and obesity makes to igniting a cascading spiral of mutually-reinforcing pathological outcomes. This reinforces the importance of intervention targeting body size and fatness. The results identify physical activity and tobacco smoking – and suggest saturated fat intake – as targets of intervention designed to restrict the growth in overweight and obesity leading to raised BP and elevated BG, and pinpoint harmful or hazardous alcohol intake as an additional target of intervention for BP reduction. For TC, the findings provide evidence of a sudden elevation in TC for Vietnamese women at around 50 years of age, and which is of potential consequence because – in Western Countries – similar elevations are a portent of the marked increase in female rates of cardiovascular disease that occurs in the sixth or seventh decade of life. The results show that this sudden elevation in TC for women, which occurs at about the same time in life as the menopausal transition, cannot be accounted for coincident sudden increases in overweight and obesity or by demographic characteristics or lifestyle factors. The findings are valuable for planning cost-effective preventive strategies and developing interventions, and for strengthening the implementation of the National Strategy on Prevention and Control of Certain Non-communicable Diseases for the Period 2015-2025 in Vietnam.

Item Type: Thesis - PhD
Authors/Creators:Tran, NTT
Keywords: body mass index, waist circumference, obesity, blood pressure, blood glucose, total cholesterol
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