Given that vitamin D is absorbed in the proximal small intestine, it is believed that vitamin D deficiency in people with a fat malabsorption syndrome may be due to decreased absorption of vitamin D. All diseases of the small bowel can cause fat malabsorption. These fat malabsorption syndromes include Crohn's disease, ulcerative colitis, or cystic fibrosis among others (1,2) and affect the amount of nutrients and fat absorbed by the gastrointestinal tract.