Vitamin D concentrations in New Zealanders with and without inflammatory bowel disease: do they differ?

Patients with inflammatory bowel disease (IBD), Crohn's disease (CD) or ulcerative colitis (UC) are at risk of low vitamin D owing to reduced absorption, medication-associated sunlight exposure restrictions and/or increased requirements due to inflammation. This study aimed to determine if the serum vitamin D concentration of New Zealand IBD patients relates to disease activity and differs from controls.

Data concerning demographics, sunlight exposure, vitamin D supplementation and disease activity were collected using a retrospective questionnaire. Serum vitamin D concentrations were measured in dried blood spots and validated against blood samples in a participant sub-group.

Vitamin D concentration was significantly increased by supplementation (82.8 v 66.4nmol/L, p<0.001) and sunlight exposure while on holiday (75.2 v 63.7nmol/L, p<0.001). Patients with CD who reported active disease in the last year had significantly lower vitamin D concentrations (68.6 v 84.6nmol/L, p=0.008) than those who reported remaining in remission.

In this cohort of New Zealand residents, mean vitamin D of patients with IBD was not different from controls. In patients with CD, recent disease activity was significantly associated with lower vitamin D. The use of vitamin D supplementation may have implications for reducing disease activity occurrence in patients with CD.