DBP and vitamin D deficiency: Patients with digestive disease are particularly prone to vitamin D deficiency due to fat malabsorption; bile salt deficiency; loss of absorptive surface; increased intestinal permeability; loss of liver function causing impaired hepatic hydroxylation of vitamin D, reduced hepatic production of vitamin D binding protein (DBP); or an impaired cutaneous production due to reduced sun exposure or jaundice [18]; [20].