LETTER TO THE EDITOR Seasonal variations in serum levels of 25-hydroxyvitamin D in patients with systemic sclerosis Bruno Seriolo & Luigi Molfetta & Maurizio Cutolo Received: 27 December 2010 / Accepted: 4 January 2011 / Published online: 15 January 2011 # Clinical Rheumatology 2011 Sir, We read with interest the work by Caramaschi et al. [1], who concluded that very low levels of 25-hydroxyvitamin D (25OHD) are common in patients with systemic sclerosis (SSc). Low 25OHD levels have already been reported in patients with SSc [2], but no data are available on seasonal variations in serum levels of 25OHD in populations affected by SSc. We studied the prevalence of vitamin D deficiency and insufficiency in a total of 53 female patients with SSc (age 58.5±7.3 years) and 35 sex-, age-, and season-matched controls (age 59.9±0.9 years) from northwestern Italy (Liguria) during the four seasons (2009–2010). Serum levels between 10 and 30 ng/ml were classified as “vitamin D insufficiency”, while concentrations <10 ng/ml were defined as “vitamin D deficiency”. During winter, vitamin D insufficiency was observed in 32 (60%) SSc patients compared with 19 (38%) age- matched controls (p <0.001), while vitamin D deficiency was observed in 5 (9%) SSc patients vs. 4 (8%) controls. However, average serum 25OHD levels were 19.3± 12.3 ng/ml (range 7.1–56.6) among SSc patients compared with 32.1±14.1 ng/ml (range 8.2–58.6) among controls (p <0.001). During summer, 34 (64%) SSc patients and 18 (36%) controls had vitamin D insufficiency (p <0.001) and 13 (24%) SSc patients vs. 1 (2%) control had vitamin D deficiency (p <0.0001). Average serum 25OHD levels were 21.7±13.4 ng/ml (range 7.4–64.6) among SSc patients compared with 39.4±15.4 ng/ml among controls (p < 0.001). Seasonal variations of serum 25OHD showing higher values in summer (21.7±13.4 ng/ml and 39.4± 15.4 ng/ml) were observed in both SSc patients and controls as compared to: autumn values (21.4±10.6 ng/ml and 36.6±9.8 ng/ml, both p <0.01), winter values (19.3± 12.3 ng/ml and 32.1±14.1 ng/ml, both p <0.001), and spring values ( 20.5±11.8 ng/ml and 35.5±10.1 ng/ml, both p <0.01). Interestingly, both SSc patients and controls showed seasonal variations in serum 25OHD levels likely due to different exposure to ultraviolet B rays according to the study period. However, average serum 25OHD levels were found significantly lower in the SSc patients compared with controls throughout the year. Our data confirm previous reports reporting low serum 25OHD levels in SSc patients [3]. The prevalence of vitamin D deficiency or insufficiency we observed in our patients is in agreement with what was observed by Camaschi et al. [1]. The significant seasonal changes we found in both SSc patients and controls, with peak values of serum 25OHD in late summer and decreased values in late winter were found in agreement with the number of hours spent outdoors. On the other hand, low serum 25OHD levels in SSc may be linked to multiple risk factors, such as insufficient sun exposure due to disability or vascular complications, or insufficient intake and malabsorption or vitamin D receptor resistance. Vitamin D plays an essential role in calcium homeostasis and it regulates intestinal absorption of dietary calcium, renal excretion of calcium, and calcium ion flux in the bones. More recently, in addition to these important metabolic activities, vitamin D is recognized to contribute to the regulation of the immune system. [4] B. Seriolo : M. Cutolo Research Laboratory and Academic Unit of Clinical Rheumatology, Department of Internal Medicine, University of Genova, Genova, Italy L. Molfetta (*) Orthopedic Unit, DINOG Department, University of Genova, Genova, Italy e-mail: seriolob@unige.it Clin Rheumatol (2011) 30:445–446 DOI 10.1007/s10067-011-1684-7