Given that individuals living in the areas with low sunlight would have a reduced level of vitamin D synthesized in their body (S2 Fig in S1 File), the carrier of the vitamin D metabolism-related gene CYP24A1 mutation may be associated with a further reduced level or loss of the physiological function of vitamin D, which may then increase the susceptibility to CRC or trigger the CRC carcinogenesis (Table 4). This evidence concerns the gene CYP24A1 and colorectal carcinoma.