The amount of vitamin D produced from winter sunlight (in Boston, MA) and dietary sources will negligibly raise blood vitamin D levels in these patients, and oral vitamin D supplementation may have limited efficacy due to malabsorption. A variety of UV light sources have been developed and sold as in-home tanning devices and to produce vitamin D in reptiles. The efficacy of correcting vitamin D deficiency by the skin exposure to an artificial source of UVB radiation in patients with fat malabsorption syndromes (Crohn's disease, ulcerative colitis, or cystic fibrosis) or after gastric bypass surgery has not been studied. The investigators have conducted a pilot study in healthy adults that demonstrated that exposure to the lamp raised the blood level of 25-hydroxyvitamin D with no side effects. The main purpose of this study is to evaluate the effect of the FDA approved artificial source of ultraviolet (UVB) radiation (Sperti® lamp) in improving vitamin D status in patients with fat malabsorption syndromes and patients who have undergone roux-en-Y gastric bypass surgery.