Seasonal variations in glycemic control of type 2 diabetes in Korean women

Seasonal variations in lifestyle, such as food intake and physical activity, have been reported. Glycemic control in type 2 diabetes mellitus (T2DM) may be affected by such changes. We investigated seasonal variations in glycemic control, food intake, and physical activity in type 2 diabetic patients. This prospective observational study included 37 Korean female patients who had < 8.0 % hemoglobin A1c (HbA1c) and managed diabetes by oral anti-diabetic drugs or lifestyle modification only. Participants underwent four or five assessments, including total physical activity (household, leisure-time, and occupational activity) (metabolic equivalent of test-h/day), food intake (kcal/day), HbA1c, and anthropometry every 3 months (August, November, February, May, and August in the Northern Hemisphere) over 1 year. When anti-diabetic drugs were changed, we analyzed the data just before the changes. The mean HbA1c levels (%) of August and November in 2008, and February, May, and August in 2009 were 7.0 +/- A 0.1, 6.9 +/- A 0.1, 7.2 +/- A 0.2, 7.4 +/- A 0.2, and 7.2 +/- A 0.2, respectively (P = 0.018). The change of HbA1c was nearly 0.5 % for the 1-year period. From August to May of the following year, there were also seasonal variations in food intake (1,872 +/- A 143, 1,739 +/- A 97, 1,673 +/- A 86, 1,561 +/- A 132, respectively; P = 0.013), and total physical activity [7.7 (3.7-14.6), 6.3 (2.8-10.4), 5.1 (2.7-12.6), and 11.2 (4.7-20.5), respectively; P = 0.048]. However, the seasonal variations of HbA1c and total physical activity became non-significant when farmers were excluded. These data suggested that glycemic control, total physical activity, and food intake varied seasonally in Korean T2DM patients. These seasonal variations should be considered in education for glycemic control.