“…Two of the 19 studies are longitudinal studies [ 40 , 42 ], 11 are case–control studies [ 20 , 35 , 37 , 39 , 43 , 44 , 46 – 48 , 50 , 51 ], while the remaining are cohort studies which only involve the hypertension group [ 34 , 36 , 38 , 41 , 45 , 49 ]. 15 studies involved participants with a mean age ranging from 40 to 65 years [ 20 , 34 – 37 , 39 – 44 , 46 , 48 – 50 ], while three studies recruited older individuals aged above 65 years [ 45 , 47 , 51 ]. Of all included studies, 12 included both normotensive control and essential hypertensive subjects [ 43 ], with both mixed genders involved [ 20 , 35 , 37 , 39 , 40 , 44 , 46 – 48 , 50 , 51 ], whereas one study investigated the association between autonomic control and vascular condition in men with essential hypertension only [ 38 ].…”