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.
Gastric bypass surgery is indicated for the surgical treatment of morbid obesity by making the stomach smaller and allowing food to bypass proximal part of the small intestine, where many minerals and vitamins are most absorbed. Food (and calorie) intake is dramatically reduced because of the new small stomach. Many patients who have bypass surgery develop nutritional deficiencies because they do not adhere to their post-operative guidelines concerning the need for nutritional supplements. Malabsorptive operations like gastric bypass surgery pose a particular risk for multiple nutritional deficiencies, including vitamin D malabsorption. (3) Vitamin D is ingested in the diet, from supplements, as well as synthesized naturally in the skin following UVB irradiation from the sun. As sunlight enters the atmosphere, all radiation below 290 nm is absorbed by the stratospheric ozone layer. Radiation between 290 and 315 nm is responsible for converting 7-dihydrocholesterol (provitamin D3) in the epidermis and dermis to previtamin D3. Once formed, previtamin D3 undergoes a thermally induced isomerization to vitamin D3. Vitamin D3 enters the circulation and is metabolized in the liver to 25-hydroxyvitamin D3 \[25(OH)D\] and then in the kidney to 1,25-dihydroxyvitamin D3 \[1,25(OH)2D\] by the 25-hydroxyvitamin D3-1á-hydroxylase \[1á-OHase\]. 25(OH)D is the major circulating form of vitamin D and is routinely measured in the blood to determine the vitamin D status of a patient.
The amount of vitamin D produced from winter sunlight and dietary sources will negligibly raise blood 25-hydroxy vitamin D levels. People living in areas that receive less sunlight have lower circulating 25-hydroxyD (the major circulating form used to measure vitamin D status) levels. Vitamin D deficiency (defined as a serum 25(OH)D level \< 20 ng/ml) in the general population is treated with oral supplementation of vitamin D at a dose of 50,000 IU given once weekly for eight weeks. (1) However from clinical experiences, oral supplementation has limited efficacy in vitamin D deficiency patients with malabsorption syndromes likely due to the inability to efficiently absorb vitamin D. \*(1-3) A variety of UV light sources have been developed and sold as in-home tanning devices and to produce vitamin D in reptiles. In a pilot study, the investigators have observed that 5 out of 8 subjects had significant increased circulating 25(OH)D after exposure to a Sperti® lamp for 24 weeks. However, the possibility of correcting vitamin D deficiency by the skin exposure to artificial source of UVB radiation in patients with fat malabsorption has not been studied.
The first aim of this study will be to evaluate the efficacy of an FDA approved artificial source of UVB radiation (Sperti® lamp) in raising serum 25(OH)D levels in patients with fat malabsorption due to Crohn's disease, ulcerative colitis, or cystic fibrosis or gastric bypass surgery and other causes. The second aim of the study is to compare the rise in serum 25(OH)D over the repeated measures in this study in patients with the 4 different skin types (types II-V).
The device that the investigators used in this study was originally designed for tanning. From our pilot study H23521 the investigators observed that much longer times were needed to increase the production of vitamin D. As can be seen in Figure 1, our healthy adults exposed to up to 10 minutes to the Sperti lamp showed significant increases in serum 25 (OH)D levels in the subjects studied. The investigators found that 5 of the 8 subjects showed significant increases in 25(OH)D. Those with skin type IV and V demonstrated minimal responses due to the sunscreening effect of their skin pigment (Fig 2). This demonstrates that skin types IV and V may require longer exposure times to achieve the 0.75 MED dose and raise the serum 25(OH)D level. However, during this pilot study, the investigators did not observe any untoward side effects (such as skin redness) associated with exposure to UVB light with longer exposure times.
