Navigating optimal blood pressure (BP) management in young- and middle-aged Thai adults diagnosed with hypertension (HTN) presents a substantial challenge, particularly in contrast to the older population. The early adoption of lifestyle modifications emerges as a pivotal factor in achieving effective BP control, especially for those recently diagnosed with HTN. Although young- and middle-aged adults in Thailand may be physically fit and capable to embrace lifestyle changes following the diagnosis of a chronic illness, their compliance to recommended lifestyle modification is suboptimal as compared to older adults with HTN. Aggravatedly, there exists a notable scarcity of evidence regarding the influence of psychosocial factors, guided by Social Cognitive Theory (SCT)—commonly utilized to illuminate the impact of such factors on human behavior—on recommended lifestyle behaviors for BP management in this targeted population. Specifically, a knowledge gap persists in understanding how psychosocial factors may affect adherence to dietary guidelines, such as low-sodium or low-fat diets (DA), and regular engagement in physical activity (PA) among Thai young- and middle-aged adults diagnosed with HTN within the first five years. Therefore, this dissertation meticulously examines the intricate relationship between SCT psychosocial factors—perceived stress, self-efficacy, outcome expectancy, functional support, and workplace support—and the adoption of recommended lifestyle behaviors, specifically DA and PA, as well as their systolic and diastolic blood pressure (BP) status among young- and middle-aged Thai adults diagnosed with HTN. The study unfolds through three key aims:Firstly, it conducts a comprehensive review of 24 studies to delve into the multifaceted associations between psychosocial factors and DA and PA. The influence of self-efficacy on both PA and DA, contingent upon different domains and countries of origin. Although social support exhibited limited associations, outcome expectancy had modest links with PA. It's noteworthy that many of these studies primarily focused on older adults with HTN. Secondly, the dissertation rigorously evaluates psychometric measures, ensuring their reliability and validity when adapted to the Thai context. This phase not only reaffirms the robustness and consistency of measures related to the DA domain but also uncovers the strength of the associations between self-efficacy, outcome expectancy, social support, workplace support, and DA. Similarly, within the realm of PA-related measures, the correlations among self-efficacy, moderate- and vigorous-intensity PA, social support, and workplace support were thoroughly explored. These psychometric evaluations had confirmed the validities and reliabilities of translated psychosocial measures (from English to Thai) within the context of DA and PA engagement in Thailand. Finally, a comprehensive study involving 400 young- and middle-aged adults with HTN is conducted to shed lights on determinants of HTN-related lifestyle behaviors. Self-efficacy in PA emerges as a pivotal predictor of PA, with functional support significantly contributing to the reduction of systolic BP. Similarly, self-efficacy in DA plays a crucial role in shaping DA and its subsequent impact on systolic BP reduction. Notably, moderate-to-vigorous PA (MVPA) acts as a significant mediator between self-efficacy in PA or functional support in PA and systolic BP. There are also notable associations between self-efficacy in PA and MVPA, especially among those with shorter HTN duration (≤1 year). Moreover, both decreased systolic and diastolic BPs are observed among adults who have engaged in an increased MVPA and low-intensity PA, as well as for those who have more complied to a low-sodium and low-fat diet.
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