Seasonal variations on endothelium‐dependent flow‐mediated vasodilation in adults with type 2 diabetes and nondiabetic adults with hypertension and/or dyslipidaemia who perform regular exercise

Introduction Endothelium‐dependent flow‐mediated dilation (FMD) of the brachial artery often changes seasonally. We aimed to examine the association between the seasonal variation on FMD and regular exercise in adults with type 2 diabetes (T2D) and nondiabetic adults with hypertension and/or dyslipidaemia (non‐T2D). Methods This retrospective study included 14 T2D and 17 non‐T2D adults, who started to perform moderate‐intensity aerobic exercise for 30‐40 min/d at a hospital gym in 2006‐2010 and maintained exercise performance at least 2 d/wk until the end of the observation period. We observed and analysed the data for 5 years (from March 2011 to February 2016). FMD, cardio‐ankle vascular index (CAVI) and metabolic outcomes were compared among seasons in the T2D and non‐T2D groups. Results The FMD values were lower in winter than in other seasons in both groups (all P < .01). The annual range of FMD was larger by 31% in the T2D group than in the non‐T2D group ( P < .05). The systolic blood pressure (BP) values were higher in winter than in other seasons in both groups (all P < .01), and the diastolic BP values were higher in winter than in summer in both groups (T2D: P < .05; non‐T2D: P < .01). CAVI and other outcomes did not change seasonally. Conclusions Flow‐mediated vasodilation showed seasonal variation in T2D adults, even if they performed exercise regularly for a long period of time. Additionally, we found that the annual range of FMD might increase with the presence of T2D.