Defining risk thresholds: Appropriate body mass index cut-off for hypertension in Thai Cohort Study

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Nipa Sakolchai
Prasutr Thawornchaisit
Ferdinandus de Looze
Christopher M Reid
Sam-ang Seubsman
Adrian Sleigh


Body mass index (BMI) is used to predict the risk of hypertension in some Western countries. But to date the appropriate BMI cut-off for hypertension among Thais remains unresolved. This study aims to determine the proper BMI cut-off for risk of hypertension in Thailand. Health-risk factors and their effects on incidence of hypertension were evaluated prospectively in the national Thai Cohort Study from 2005 to 2013. All derived from 40548 initially normotensive Sukhothai Thammathirat Open University students returning mail-based questionnaire surveys in both 2005 and 2013. Adjusted relative risks of association between baseline BMI and 8-year incidence of hypertension were calculated after controlling for a wide array of confounding factors. A smooth model with a linear fit of associations between BMI and hypertension risk was compared to a non-linear model using cubic splines. In Thailand, the 8-year incidence of hypertension was 5.1% (men 7.1%, women 3.6%). Hypertension was strongly associated with ageing and high BMI. Non-linear modelling showed the best fit with a significant upwards inflection pointing to the risk threshold occurred in the third BMI category of 20.75 (aRR = 1.89, 95% CI 1.54-2.32) compared to a reference BMI of 20.00 kg/m2. The health risk transition Thailand has led to a rising prevalence of hypertension which is an important risk factor for many chronic diseases. A BMI cut-off point of 21 kg/m2, two points lower than the current 23 kg/m2, would be appropriate for defining the threshold of hypertension risk in Thai adults. Lowering BMI cut-off for risk of hypertension will encourage people to have more awareness of their health. Our results support population level interventions design to increase exercise and decrease overweight and obesity in Thailand.

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Sakolchai, N., Thawornchaisit, P., de Looze, F., M Reid, C., Seubsman, S.- ang, & Sleigh, A. (2019). Defining risk thresholds: Appropriate body mass index cut-off for hypertension in Thai Cohort Study. Interdisciplinary Research Review, 14(4), 25–33. Retrieved from
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