Dear Editor, Vitamin D is of increasing interest in multiple specialities including rheumatology due to its role in bone and calcium homeostasis as well as emerging immune-modulating effects [1]. We therefore read with interest the recent article by Haroon et al. concerning the prevalence of vitamin D deficiency amongst newly referred rheumatology outpatients in Cork, Ireland between January and June 2007 [2]. Seasonal variation is an important aspect of vitamin D biology in northern latitudes, such as in the UK. In the light of the findings of Haroon et al., we aimed to explore this variable in more depth over a full year, whilst seeking any relationship between vitamin D levels and progression to particular diagnostic outcomes. Vitamin D levels are routinely measured on all patients attending an early arthritis clinic at The Freeman Hospital, Newcastle upon Tyne, UK, and we audited the data from this more recent inception cohort recruited over a full 12-month period. Consecutive patients presenting to the Newcastle early arthritis clinic between January–December 2009 were recruited, and their vitamin D levels were checked using the DaiSorin Liaison automated immunoassay. Final diagnoses were defined after a minimum of 1-year follow-up by the consulting rheumatologist to minimise classification error. We chose the same parameters as Haroon et al. [2] to define vitamin D deficiency, i.e. 25–53 nmol/L, deficiency and <25 nmol/L, severe deficiency. The final cohort included 210 patients [median age 48 (range, 16–97), 37% male, 63% female], and diagnostic outcomes were determined for 206 of these patients (four patients were lost to follow-up). In our cohort, 41 (20%) had rheumatoid arthritis (RA), 29 (14%) had osteoarthritis, 75 (36%) had other inflammatory joint diseases and connective tissue disorders (excluding RA), i.e. psoriatic arthritis, ankylosing spondylitis, etc., 56 (27%) had noninflammatory arthralgia or fibromyalgia and five (2%) had a crystal arthropathy. Overall, 135 (64%) had vitamin D levels <53 nmol/L, i.e. were deficient and 41 patients (20%) had vitamin D levels <25 nmol/L, i.e. severely deficient. This correlates with the findings of Haroon et al. where 71% were vitamin D deficient and 26% were severely deficient. We next compared the final diagnosis and vitamin D levels on a diagnostic (Fig. 1a) and quarterly basis (January–March, April–June, July-September and October– November) (Fig. 1b) to ascertain if either seasonal fluctuation of vitamin D or absolute levels had any effect on the diagnostic outcome. As expected, there is an increased incidence of vitamin D deficiency in the winter months; however, we demonstrate that this deficiency may partially extend F. A. H. Cooles (*) :A. G. Pratt : J. D. Isaacs :W.-F. Ng Musculoskeletal Research Group, Institute of Cellular Medicine, Newcastle University, 4th floor Catherine Cookson building, Framlington Place, Newcastle upon Tyne NE2 4HH, UK e-mail: faye.cooles@ncl.ac.uk