TABLE 3.

Summary on the roles of vitamin D (VD) in CP from clinical studies.

Country	Research type	Number of patients	Aim of the study	RR/HR/OR (95%CI, p)	Conclusion	References
Spain	Meta	548	To determine the prevalence of fat-soluble vitamin deficiency in CP patients	1.17 (0.77–1.78, p = 0.46) I2 = 0%	Fat-soluble vitamins deficiency is frequent in CP patients, but no significant increased risk of VD deficiency	Martínez-Moneo et al. (2016)
Netherlands	Meta	465	To determine the prevalence of VD insufficiency and deficiency in CP patients	1.14 (0.70–1.85, p > 0.05) I2 = 0%	High prevalence of VD insufficiency and deficiency in CP patients, but no significant difference between patients and healthy controls	Hoogenboom et al. (2016)
Germany	Meta	220	To analyze the results from RCTs of dietary interventions for CP patients and make further dietary recommendations	Not available	VD can improve VD deficiency in CP, while other nutritional support therapies have no evidence of effectiveness	Wiese et al. (2021)
Denmark	RCT	30	To assess intestinal absorption of cholecalciferol in patients with CP and fat malabsorption	p < 0.001	Daily VD supplementation increased 25(OH)D3 in CP patients compared to placebo, but this was not the case with weekly tanning bed sessions	Bang et al. (2011)
Denmark	RCT	30	To investigate the effect of changes in 25(OH)D3 and 1,25(OH)2D3 on Tregs in patients with CP with fat malabsorption	p < 0.05	Changes in VD significantly correlate with maturation of CD4+ and CD8+ Tregs	Bang et al. (2012)
India	RCT	40	To assess the relative efficacy of two different doses of VD in patients with CP with VD deficiency	p < 0.001	The 600,000 IU dose was more effective in achieving VD sufficiency over 6 months compared to 300,000 IU, but no longer after 9 months	Reddy et al. (2013)

CP, chronic pancreatitis; RCT, randomized controlled trial; VD, vitamin D; Tregs, regulatory T cells; RR, relative risk; HR, hazard ratio; OR, odds ratio; CI, confidence interval.