We will then discuss potential vulnerability and protective characteristics that may moderate the association between OSA and cognitive decline, namely, age, sex, menopause, obesity, diabetes mellitus, hypertension, cardiovascular diseases, smoking, excessive alcohol consumption, depression, air pollution, Apolipoprotein E ε4 (ApoE4) allele, physical activity, and cognitive reserve. Here, APOE is linked to obstructive sleep apnea syndrome.