Thailand has been transforming from a developing to a newly industrialized country as a result of rapid economic growth over the past two decades. This transition involves changes in many factors, from downstream to upstream, which have health-risk impacts. The Thai Cohort Study (TCS) was initially established in 2005 to assess this transition in health-risk factors in Thailand and the cohort has been followed up every four years to evaluate the change in risk factors and chronic disease outcomes. Hypertension is an important risk factor for both cardiovascular and cerebro-vascular disease, so the focus of this study is to evaluate the change in health-risk factors and the effects on hypertension over a four-year period. All data in the TCS were acquired from questionnaires. An additional aim of this thesis was to validate the reporting of ‘hypertension diagnosed by a doctor’ to determine the accuracy of such self-reported hypertension since it was an important dependent variable for the rest of the study.
The baseline TCS study of the effects of health-risk factors on hypertension gathered data from 87,143 students of STOU in 2005. The alteration of health-risk factors and their effects on hypertension after a four-year period used data obtained from 60,569 participants who also participated in the 2009 TCS 4-year follow-up survey. Two hundred and forty (240) participants from the 2009 survey who reported ever being diagnosed by a Doctor with "hypertension" or reporting "no hypertension" were randomly selected and matched for age, sex and other characteristics. The participants were interviewed via telephone using a structured questionnaire administered by a Thai physician to determine the accuracy of the self-reported hypertension. Data were separately analyzed by sex and separated into 2 age groups, younger (≤ 40 years) and older (>40 years). Crude and adjusted odds ratios of association between each risk factor and hypertension status were analyzed across the 2 age groups by sex. Crude and adjusted relative risks were separately calculated by sex for the association of each risk factor and incidence of hypertension after 4-year follow-up. Agreement, sensitivity, specificity, positive and negative predictive values (PPV&NPV) were calculated by comparing the results of self-report and physician interview report of hypertension.
The agreement between self-reported and physician interview reporting of hypertension was moderate (К=0.5) and sensitivity and specificity were 82.4% and 70.65% respectively. Overall, the accuracy of self-reported hypertension in the TCS was 75.2% which was acceptable for the study of trends and risks in large population-based samples such as TCS.
In the TCS, the prevalence of hypertension between 2005 and 2009 increased with the rates for adults in 2005 and 2009 being 4.6% and 6.1% respectively. The rate was higher in males than in females in both surveys (6.9% vs 2.6% in 2005 TCS; 9.4% vs 3.4% in 2009 TCS). In 2005, hypertension was associated with ageing, a lower education attainment, a higher BMI and having underlying diseases namely diabetes mellitus, high blood lipids and kidney disease in both sexes. Lower education was associated with a higher risk of hypertension in the younger males and females (≤40 years) while kidney disease was associated with an increased risk of hypertension in younger females. In both sexes, the prevalence of obesity, diabetes mellitus and high blood lipids was higher in 2009 than in 2005 while the rate of kidney disease was lower. Changes in these risk factors over the 4 years may be associated with the increased rates of hypertension observed in 2009. In this cohort, the incidence of hypertension after 4-year follow up in Thai adults was 3.5% and the rate in males was substantially higher than the corresponding rate in females (5.2% vs. 2.1%). Hypertension incidence was associated with ageing, being obese and having underlying diseases including diabetes mellitus, high blood lipids and kidney disease in both sexes. In males, it was also related to consuming instant foods, physical inactivity, smoking and drinking alcohol. In females, having a partner was correlated with a higher risk of hypertension.
Economic development is associated with an increase in the prevalence of hypertension. The risk of hypertension is associated with ageing, obesity, diabetes mellitus, high blood lipids and kidney disease. Socio-economy has no influence on risk of hypertension incidence so the Thai health-risk transition is likely to be in the middle stage of the pattern between developing and developed countries.
Self-reported hypertension validity was shown to be acceptable for a national survey. These data suggest that it may be essential to implement policies for screening and preventing diseases facilitating hypertension such as obesity, diabetes mellitus, kidney disease and high blood lipids. Limitation of salt in ready to eat or industrial foods will reduce daily salt consumption in Thai population. Thais should be encouraged to pursue higher education, consume healthy food, maintain normal BMI, drink less alcohol and stop smoking.