Seasonal Variation of HbA1c in Intensive Treatment of Children with Type 1 Diabetes

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Abstract
Objective: The aim of this study was to measure whether there is a seasonal variation in glycosylated haemoglobin concentrations and insulin dose used in the intensive treatment of children with type 1 diabetes, and whether such variation is related to severe hypoglycaemia. Patients: A geographic population of 114 intensively treated type 1 diabetic patients < 19 years of age, mean 12.7 (SD 4.3) years, with diabetes onset before 1995, were studied in a cohort 1995-96. Methods: Hb(A1c) insulin doses and severe hypoglycaemia were registered at regular visits scheduled quarterly, but not standardised in time, Seasonal mean values were calculated for HbA(1c), and insulin dose. Results: Lower HbA(1c) was seen in spring and summer, and higher in autumn and winter (p=0.023). Patients reporting severe hypoglycaemia had a seasonal variation in HbA(1c) (p=0.019) and a tendency to seasonal variation in insulin dose, while patients not reporting severe hypoglycaemia did not vary in HbA(1c) or insulin dose. Conclusions: Self-control and adjustment of insulin doses to seasonal change need to be improved also in intensively treated children, with regard to the risk for worsened metabolic control after the summer and increased severe hypoglycaemia in spring and early summer. The findings have important implications for design of short-term studies of metabolic control.