jn.nutrition.org/content/132/8/2382S.full
The roles of nutrients in DNA methylation, especially in genome-wide methylation, have also been described. Zinc deficiency can reduce the utilization of methyl groups from S-adenosylmethionine (SAM) in rat liver and results in genomic DNA hypomethylation as well as histone hypomethylation (20,21). Dietary deficiency in selenium decreased genomic DNA methylation in Caco-2 cells and in the rat liver and colon (22,23). Vitamin C deficiency has been associated with DNA hypermethylation in lung cancer cells (24,25). Interestingly, niacin, precursor of NAD+, is required to maintain the unmethylated state of CpG dinucleotides by inhibiting the enzymatic DNA methylation (26,27), because it is necessary for the synthesis of poly-ADP–ribose polymerase-1, which converts histone H1 to poly-ADP–ribosylated forms. The poly-ADP–ribosylated forms of histone H1 are responsible for the enzymatic inhibition of DNA methylation (26,27).