Objective: In the U.K. Prospective Diabetes Study, A1C increased from 1.2 to 1.7% and fasting plasma glucose from 1.0 to 2.8 mmol/l over 10 years in type 2 diabetic patients. It is not known whether the blood glucose increase observed in long-term studies of type 2 diabetes results from small, steady increases throughout the year or from increases during discrete periods.
Research design and methods: To estimate the variation of actual glycemic control and its relation to holiday times, we measured A1C and fructosamine in 110 patients with type 2 diabetes. These measurements were performed four times at intervals of 4-6 weeks; therefore, glycemic change was determined for three periods: preholiday period (from between November 13 and December 20 to between December 20 and January 20), holiday period (from between December 20 and January 20 to between January 28 and February 28), and postholiday period (from between January 28 and February 28 to between March 1 and April 10). A final measurement of A1C was obtained from 90 subjects in the following December or January.
Results: The mean A1C increased, but not significantly, during the preholiday (increase 0.135 +/- 0.723%, P = 0.055) and holiday (increase 0.094 +/- 0.828%, P = 0.239) periods. The mean A1C decreased, but not significantly, during the postholiday period (decrease 0.022 +/- 0.588%, P = 0.695). Altogether, the A1C change during these three periods increased significantly (increase 0.207 +/- 0.943%, P = 0.024). The mean fructosamine increased significantly during the preholiday period (increase 0.151 +/- 0.460 mmol/l, P = 0.001), but there was no significant change during the holiday period (increase 0.057 +/- 0.593 mmol/l, P = 0.321). However, fructosamine decreased significantly during the postholiday period (decrease 0.178 +/- 0.448 mmol/l, P < 0.001). Altogether, the fructosamine changes during the study periods showed no significant difference (increase 0.030 +/- 0.566 mmol/l, P = 0.579). Between March or early April and the following December or January, there was no additional change in A1C (decrease 0.009 +/- 1.039%, P = 0.935) for the 90 participants who returned for follow-up treatment.
Conclusions: The present study demonstrates an influence of winter holidays on the glycemic control of patients who have type 2 diabetes, and this poor glycemic control might not be reversed during the summer and autumn months. Therefore, the cumulative effects of the yearly A1C gain during the winter holidays are likely to contribute to the substantial increase in A1C that occurs every year among type 2 diabetic individuals.