This book chapter advances SDG #3 and #10 by reviewing the observed epidemiological links between normal and abnormal diurnal and seasonal rhythmicity, cognitive impairment, and ADRD. Then reviewing normal diurnal and seasonal rhythms of brain epigenetic modification and gene expression in model organisms. Finally, reviewing evidence for diurnal and seasonal rhythms of epigenetic modification and gene expression the human brain in aging, Alzheimer's disease, and other brain disorders.