*3.2.1 Mechanism*

Underlying mechanisms for an effect of vitamin D on CRC have been predominantly studied in vitro and experimental models. Hence, limited data is available in humans [8]. However, these studies suggest a role of circulating vitamin D through its active form, 1 α, 12-dihydroxyvitamin D3 [1,12(OH)2D3], in controlling cell growth, by reducing proliferation and by inducing differentiation and apoptosis [4, 40]. Other alleged mechanisms related to a higher vitamin D status are related to improved innate and adaptive immune function, inhibition of angiogenesis, reduced inflammation, and regulation of microRNA expression [4, 40–42], as well as inhibition of invasion and metastasis and suppression of angiogenesis [4].
