Does seasonal level of serum 25-OH vitamin D correlate with the activity of Crohn's disease?
BACKGROUND AND AIM
Vitamin D has immune modulating effects and normal to high levels might be correlated with less severe Crohn's disease (CD). We aimed to review seasonal vitamin D levels in CD patients in correlation with disease activity.


METHODS
CD patients were identified from an inflammatory bowel disease (IBD) database and given two questionnaires enquiring about vitamin D supplementation, sun exposure, sunblock application and symptoms to complete the CDAI. Participants were examined and serum 25-OH vitamin D [25(OH)D] levels and haematocrit were determined in winter (06/2011-09/2011) and summer (12/2011-03/2012). Patients taking vitamin D supplements or with extensive small bowel resection were excluded.


RESULTS
32 patients (19 women, mean age 39 plus or minus 16 years, range 18-73 years), from Dunedin, New Zealand (45 degrees 52' S, 170 degrees 30' E) consented to participate in the study. Of these, three took vitamin D supplements and were excluded. In winter 76% of the participants had serum 25(OH)D levels classified as deficient (<50 nmol/L) and all of them had insufficient 25(OH)D levels (<75 nmol/L). In summer, serum 25(OH)D levels were deficient only in 10% but insufficient in 55% of the participants. Mean serum 25(OH)D level was 35.9 nmol/L (norm 50-150nmol/L) in winter (range 5-67, SD 17.5) and 69.6 nmol/L in summer (range 13-119, SD 19.0) (p<0.0005). There was no significant difference in the seasonal levels of serum 25(OH)D between male and female participants (p=0.601). Mean CDAI score was 103.9 in winter (range -10-262, SD 76.9) and 90.2 in summer (range -13-331, SD 84.0) (p=0.365). A mixed-effects regression analysis showed no statistically significant correlation between seasonal levels of serum 25(OH)D and CDAI (p=0.612) among our study participants.


CONCLUSION
Suboptimal levels of serum 25(OH)D were found in the majority of our study participants particularly in winter and they would benefit from supplementation. Our study showed no statistically significant correlation between seasonal serum 25(OH)D levels and CD activity. Given the limitations of the study, the role of 25(OH)D as a predictor of disease activity could not be clearly concluded.