**15.3 Vitamin D and sunlight exposure**

Vitamin D deficiency is common amongst IBD patients. Recent studies have shown suboptimal levels of Vitamin D in 57 to 78% of recently diagnosed patients with IBD (Leslie et al., 2008, Bours et al., 2010). The protective role of Vitamin D has been investigated in a number of malignancies including prostate, colon, lung, pancreatic, endometrial, breast and even skin cancer (Schwartz and Skinner, 2007). The paracrine and autocrine effects of extrarenal 25-hydroxy-Vitamin-D3 via the nuclear Vitamin D Receptor (VDR) include regulation of cell cycle proliferation, induction of apoptosis and increased cell differentiation signalling.

Recent epidemiologic studies demonstrate a reduction in NHL risk with increased sunlight exposure (Armstrong and Kricker, 2007). As sunlight is a major vitamin D source, it has been suggested that vitamin D status may mediate this observed association. A recent review of the literature could not conclude or dismiss a link between vitamin D insufficiency and lymphoma due to confounding findings in a number of studies and the limitations on the accuracy of dietary history taking which was the most frequent methodology in these studies (Kelly et al., 2009).

The role of Vitamin D in lymphomagenesis in the IBD population has not been investigated and warrants further study.
