Seasonal variation of serum 25-hydroxyvitamin D levels in adult patients with inflammatory bowel disease

SUMMARY: Patients with inflammatory bowel disease (IBD) are at risk of osteoporosis. Vitamin D (vitD) deficiency is known as a risk factor of osteoporosis. We observed low vitD blood levels in adult IBD patients both at the end of summer and winter. Furthermore, effects of oral vitD supplementation in (generally low) daily dosages were poor. INTRODUCTION: Patients with IBD are at risk of osteoporosis. This study evaluates seasonal vitD status, determinants of vitD deficiency and effects of vitD supplementation in adult IBD patients. METHODS: Patients were screened for vitD deficiency at the end of summer and winter using serum 25OHD(3) (cut-off point, <50 nmol/L) combined with routine laboratory tests. A standardized questionnaire was used for demographic/lifestyle data i.e. IBD activity, health behaviour and vitD intake through diet and ultraviolet light. RESULTS: Late-summer, 39% of the included 316 patients were vitD deficient. Late-winter, 57% of the follow-up patients (n = 281) were deficient. Independent protective determinants of vitD deficiency were oral vitD supplementation (summer/winter: odds ratio [OR], 0.52 [95% confidence interval [CI], 0.29–0.94]/OR, 0.44 [95% CI, 0.26–0.75]), recent sun holiday (summer: OR, 0.42 [95% CI, 0.24–0.74]) and regular solarium visits (summer/winter: OR, 0.28 [95% CI, 0.13–0.63]/OR, 0.17 [0.06–0.50]). IBD activity (p = 0.031), red blood cell distribution width (RDW; p = 0.04) and erythrocyte sedimentation rate (p = 0.03) were associated with low vitD levels using univariate analyses of the extreme 25OHD quartiles. In a subgroup with vitD supplementation, still 30% (late-summer) and 44% (late-winter) were vitD deficient. CONCLUSION: VitD deficiency is common in IBD patients, but prevalence might be comparable with the general population. Ultraviolet light is essential for adequate vitD levels. Effects of oral vitD supplementation in (generally low) daily dosages are poor. Determinants for low vitD levels were IBD activity and elevated inflammatory markers, suggesting that increased risk of osteoporosis in IBD might be more related to the inflammation than to vitD deficiency.