Descriptive information of age-modified CpG sites. (A) Schema showing the time points analysed, number of samples (n) and the number of differentially methylated CpGs based on age and individual. (B) Filtering steps on the 853 age-modified CpGs. (C) Chromosomal distribution of age-modified CpGs in relation to the expected proportions according to the location of all probes in the 450 K assay. (D) Distribution of age-modified CpG sites within RNA coding regions or intergenic regions in relation to the expected proportions of all probes in the 450 K assay. (E) Number of age-modified CpG sites that were found homogeneously methylated in seven populations of sorted blood leukocytes, granulocytes and peripheral blood mononuclear cells (PBMCs) from healthy adults as described in . The list of age-modified CpG sites with homogeneous methylation in sorted leukocytes is presented in Additional file 1.