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.