Vitamin D is essential to human health. Its important role in calcium absorption which subsequently affects bone health has been found for a long time. In recent years, a large number of scientific researches indicated a great association of vitamin D with a wide range of chronic disease, including common cancer, cardiovascular disease, autoimmune diseases, and infectious disease. More importantly, increasing evidence demonstrated that vitamin D has a positive impact in improving, as well as decreasing the incidence of the conditions mentioned above. Therefore there is a great need for vitamin D supplementation across the lifespan.

Vitamin D as a treatment or prevention of different conditions

Vitamin D deficiency has been found in a serial of diseases. The long-known examples include osteoporosis and osteomalacia, in which cases vitamin D deficiency results in Ca malabsorption. More recently, vitamin D deficiency is associated with a wider range of conditions such as cancer, hypertension, and diabetes to name a few. Although whether vitamin D deficiency is the direct cause of these conditions needs further investigation, yet vitamin D supplementation provides as a good prevention or treatment of these diseases. Table 3 summarizes the usage of vitamin D in major conditions. More conditions can be found in the scale bar in figure.5

Particular target groups - People who can not take vitamin D orally

As it can be seen from Figure.1, vitamin D can either be taken from diet in Gastrointestinal Tract (GI Tract) or formed by interaction with sunlight in skin. However, people with abnormalities in their GI tract can not absorb vitamin D through GI as it is illustrates in figure.6. Thus a UV lamp, which can help the formation of vitamin D through skin, is their major source of vitamin D.

These conditions include:

• Gastric bypass surgery

• Inflammatory bowel disease

• Bowel resection

• Cystic Fibrosis

Gastric bypass surgery

Gastric bypass surgery (GBP) is used to treat severe obesity. As the rate of obesity continues to rise in recent years, the demand for this surgery continues to increase. In GBP, the sites of duodenum and proximal jejunum, which are the preferential sites for the absorption of calcium, are bypassed. The remaining small intestine can only absorb calcium through a less efficient mechanism. A number of studies showed that people who underwent GBP suffered from calcium and vitamin D deficiency which resulted in decreased bone mass [92] and more seriously, osteomalacia [93-95]. It is reported that gastric bypass patients who don't take regular vitamin D supplementation consume only about 50% of the recommended daily requirements of vitamin D [96]. Recent study, however, showed that this deficiency can not be corrected by standard multivitamin supplementation. This can be explained as oral supplementation can not be absorbed efficiently as GI tract can not function properly. Therefore UV lamp provides an alternative in keeping normal level of vitamin D

Inflammatory bowel disease

Inflammatory bowel disease (IBD) is a group of inflammatory conditions of the large intestine and small intestine. Crohn's disease (CD) and ulcerative colitis (UC) are the two major types of IBD. Vitamin D deficiency and decreased bone mineral density are highly prevalent in IBD, especially CD [97]. One study showed that the risk of hip fracture was increased by 86% in patients with CD and by 40% in patients with UC [98]. An updated investigation reported that malabsorption of vitamin K and D is probably the cause of decreased bone mineral density, which increases the risks of fracture [97]. Even dietary intake of these vitamins was above the adequate intakes in IBD patients, the deficiency still exists. This suggests that supplement could not be a good option of correcting vitamin deficiency in IBD. In this case, a UV lamp holds a promising implication by boosting vitamin D content relying on skin instead of bowel.

Bowel resection

A bowel resection is a surgical procedure in which a part of the large or small intestine is removed. Research revealed that vitamin D deficiency is common (38.1%) in patients with small intestinal resection and was accompanied by increased marker of bone resorption and decreased bone mineral density. UV lamp has been used in treating vitamin D deficiency in patients after undergoing bowel resection. It proved that UVB radiation is more efficient in improving vitamin D in treating a patient with only 2 feet of small intestine remaining after 2 bowel resections [99].

Cystic Fibrosis

Cystic fibrosis (CF) is the UK 's most common life-threatening inherited disease. CF affects the internal organs, especially the lungs and digestive system, by clogging them with thick sticky mucus. Osteoporosis and fracture are common in children and adults with CF. Despite oral supplements (400 to 800 IU daily), vitamin D deficiency is also common and is associated with sever demineralization at the lumbar spine and hip. Thus oral supplementation may not be an effective way of maintaining normal vitamin D stores in CF [100]. As it is in bowel resection, UV lamp has also been used for boosting vitamin D and demonstrated as an excellent alternative.

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