Lay summary
Vitamin D is known for its immunomodulating properties, playing a critical role in regulating immune system responses. Previous research has shown that low Vitamin D levels may contribute to the development of uveitis, an inflammatory eye condition. HLAB27-associated uveitis is the most frequent type, accounting for 20% of cases, and is linked with ankylosing spondylitis in one-third of patients. Our research has identified a strong seasonal variation in the incidence of HLAB27-associated uveitis, with higher rates observed during winter. This seasonal pattern is even more pronounced in non-Caucasian individuals. We postulate that low Vitamin D levels during winter months may play a significant role in this variation. This study aims to explore the role of Vitamin D levels in HLAB27-associated uveitis and will lay the groundwork for a potential randomised controlled trial to determine if treating Vitamin D deficiency can reduce the frequency and severity of disease recurrences.