<p>Online health communities (OHCs) have emerged as a potentially effective tool for alleviating chronic diseases and improving mental well-being. This study examines the impact of OHCs on the psychological well-being of individuals seeking support for diabetes, as well as the underlying mechanisms from the perspective of social support theory. This study finds that obtaining robust social support through OHCs can significantly enhance various bodily functions, including those of the cardiovascular, immune, metabolic, nervous, and endocrine systems, and decrease depression, anxiety, and stress, while also improving cognitive abilities. It reveals that informational, emotional, and network support in OHCs can improve support seekers’ mental health, enhance therapeutic self-efficacy, sense of control, self-confidence, self-esteem, and self-worth, alleviate undesirable emotions, such as anxiety, depression, and distress, and provide a sense of belonging. This study can significantly benefit researchers and practitioners working in the field of OHCs by enhancing their effectiveness in supporting individuals with chronic illnesses, such as diabetes, ultimately leading to improved health outcomes and overall well-being for community members.</p>