BACKGROUND: Vitamin D is beneficial for musculoskeletal health. Although low levels of vitamin D are linked to increased pain in knee osteoarthritis (OA), their association with functionality remains understudied. OBJECTIVE: This study aimed to investigate the association between vitamin D deficiency and functional status in elderly individuals with OA and explore the potential correlation between vitamin D deficiency and plasma levels of tumor necrosis factor alpha (TNF-α) and interleukin-6 (IL-6). METHODS: The study included older adults (≥60 years) from an ageing study, encompassing 105 OA patients and 152 controls. OA diagnosis was confirmed radiographically, and the WOMAC questionnaire assessed functional impairment in these patients. Blood samples were collected to measure 25(OH) vitamin D levels by chemiluminescence and TNF-α and IL-6 levels by ELISA. RESULTS: Patients with vitamin D insufficiency/deficiency exhibited more severe cases of OA compared to those with normal vitamin D levels ( CONCLUSIONS: Reduced levels of vitamin D are associated with more severe cases of hip and knee osteoarthritis, increased pain, greater functional impairment, and elevated serum levels of TNF-α and IL-6. Further research is required to elucidate the mechanisms underlying the influence of vitamin D on osteoarthritis and to evaluate the potential benefits of vitamin D supplementation for mitigating disease symptoms and progression.