A significant health concern globally is the widespread lack of vitamin D, especially among individuals struggling with obesity. However, the reasons for this deficiency in obese individuals and the effects of weight loss, particularly through bariatric surgery, are not fully understood. Therefore, our study aims to clarify these matters. We aim to understand the broader impacts of Roux-en-Y gastric bypass (RYGB) surgery, beyond weight loss alone, especially concerning vitamin D levels in obese individuals. This understanding is crucial for healthcare professionals, especially those involved in bariatric care, as it informs clinical decisions, such as what kind of bariatric surgery, and patient education about the long-term consequences of such procedures, including the necessity for certain vitamin D supplements. Moreover, our research has implications for public health policies and services. By identifying the causes of vitamin D deficiency in obese individuals, we may develop more effective strategies for managing and preventing such deficiency in this population. Although weight loss is beneficial for overall health in obese individuals, addressing vitamin D deficiency may require additional interventions, such as increased vitamin D supplementation, less covering up when going outside or other medical treatments. Additionally, our study aims to raise awareness about the complex relationship between obesity, bariatric surgery, and vitamin D levels. This knowledge can empower individuals to make informed lifestyle choices, promote healthier behaviors, and potentially reduce the prevalence of obesity-related health issues.