Background: Vitamin D is considered as a potential immunomodulator in inflammatory bowel disease development; however, emerging evidence remains inconsistent. We aimed to investigate prospective association between serum vitamin D level and long-term risk of elderly-onset inflammatory bowel disease in a large-scale cohort.

Methods: Participants without inflammatory bowel disease at enrollment from the UK Biobank were included. Baseline blood samples were collected and serum 25-hydroxyvitamin D (25(OH)D) levels were measured. Participants were classified as vitamin D deficiency (<50 nmol/L), insufficiency (50-75 nmol/L) or sufficiency (≥75 nmol/L) based on predefined cutoffs. Primary outcome was incident elderly-onset inflammatory bowel disease, including ulcerative colitis and Crohn's disease. Hazard ratio (HR) and 95% confidence intervals (CIs) of related associations were determined using multivariable Cox regression.

Results: Among 357,656 participants (mean age, 57.9±6.9 years), 196,499 (54.9%) and 121,035 (33.8%) had vitamin D deficiency and insufficiency, respectively. During median 13.3 years' follow-up, 1,622 elderly-onset inflammatory bowel disease cases were identified. Compared with vitamin D sufficiency, no associations with vitamin D deficiency (HR=0.91, 95%CI: 0.78-1.07) or insufficiency (HR=0.86, 95%CI: 0.73-1.01) were observed for elderly-onset inflammatory bowel disease. Similarly, no associations with per 10 nmol/L increase of serum 25(OH)D were detected for elderly-onset inflammatory bowel disease (HR=1.00, 95%CI: 0.98-1.03), ulcerative colitis (HR=1.00, 95%CI: 0.97-1.03) or Crohn's disease (HR=1.01, 95%CI: 0.97-1.05). Compared with the lowest quartile, no associations with higher quartiles of serum 25(OH)D were observed for inflammatory bowel disease (HRQ4VSQ1=1.03, 95%CI: 0.89-1.19), ulcerative colitis (HRQ4VSQ1=1.06, 95%CI: 0.90-1.26) or Crohn's disease (HRQ4VSQ1=0.93, 95%CI: 0.73-1.20). Further sensitivity and subgroup analyses demonstrated similar results.

Conclusions: Serum vitamin D level or deficiency status is not associated the development of elderly-onset inflammatory bowel disease, ulcerative colitis or Crohn's disease.