Crohn's disease (CD) and ulcerative colitis (UC) are two major types of inflammatory bowel disease (IBD) that are identified by different clinical, endoscopic, pathological, and radiologic diagnostic methods.

In the past few years, the incidence of inflammatory bowel disease has been increasing worldwide, with the incidence of UC being higher than that of CD.

Vitamin D is a fat-soluble vitamin that is produced in the skin by a UV-dependent reactionand then hydroxylated by the kidneys and liver, and is converted to its active form, 1,25-dihydroxyvitamin D.

Vitamin D deficiency is common throughout the world and its deficiency rates ranging from 30 to 50% have been reported.

Several studies have shown the role of vitamin D as a regulator of the immune system and its inhibitory function incellular immunity and production of pro-inflammatory cytokines that play a major role in autoimmune diseases.

In some human studies, the link between vitamin D levels and the disease severity of IBD has been shown, but it is not clear whether lack of vitamin D is the cause or consequence.

In this study, we aimed to investigate the relationship between inflammatory bowel disease and itsflare-up with serum levels of vitamin D

Inclusion Criteria:

• Adults aged ≥18 years
• Diagnosed with crohn's and ulcerative colitis
• Regular follow-up in IBD clinic
• Recent vitamin D and disease activity assessment (within 1 month)

Exclusion Criteria:

• Current vitamin D supplementation(>1000IU/day)

  • History of malabsorption syndromes (e.g.,celiac disease)
  • Chronic kidney or liver disease
  • Pregnancy

• Adults aged ≥18 years
• Diagnosed with crohn's and ulcerative colitis
• Regular follow-up as an outpatient in the IBD clinic at Al-RAGHI hospital Assuit university
• Recent vitamin D and disease activity assessment (within 1 month)
• Sample Size Calculation:

Assuming an expected prevalence of vitamin D deficiency in IBD patients around 50%, a sample size of n = 100-150 will give adequate power (80%) to detect significant correlations (p < 0.05) between vitamin D levels and disease activity indices.