Seasonal Trends in HbA1c Level in Adult Patients with Type 1 Diabetes Treated with Personal Insulin Pumps

Introduction/Aim: The DCCT and other studies showed that the variability in HbA1c added to mean HbA1c increases the risk of the development of complications of diabetes. There were some earlier reports showing a seasonal variability in the HbA1c level in a pediatric population.

Methods: We evaluated seasonal HbA1c changes over a period of 9 years (2009-2017) in 453 adults with type 1 diabetes (T1DM) treated with personal insulin pumps. HbA1c was measured at a tertiary care university hospital on the Bio-Rad D10 hemoglobin testing system. Differences between groups (12 groups for 12 months and 6 for every consecutive two months) were assessed using the Kruskal-Wallis and post-hoc tests.

Results: Patients median age was 24 years [range 18-80 years], median BMI 22.9 kg/m2 [15.6-43.7 kg/m²], median diabetes duration 12 years [1-40 years] and median duration on personal insulin pump 6 years [0-18 years]. A total of 1, 438 HbA1c measurements were analyzed. Median HbA(1c) level for the whole study period was 7.25% [55.7 mmol/mol] (range 4.8-12.8% [29-116.4 mmol/mol]). There were seasonal differences in HbA1c over 12 months (p=0.02): The lowest HbA1c was observed in summer (July, 6.8% [50.8 mmol/mol) and the highest in winter months (from 7.1% [54.1 mmol/mol] in January to 7.3% [56.3 mmol/mol] in February). HbA1c was lower in July than in February (p=0.03). After combining two consecutive months in one group seasonality of HbA1c values was still observed (p=0.008). Median HbA1c in July/August (6.9% [51.9 mmol/mol]) was lower than in January/February (7.2% [55.2 mmol/mol], p=0.01) and in November/December groups (7.3% [56.3 mmol/mol], p=0.02).

Conclusion: To our knowledge this is the first report concerning HbA1c seasonal fluctuations in well controlled cohort of adult T1DM patients treated with insulin pumps. Seasonal changes of HbA1c levels (peak in summer months, drop in winter months) in such a group of patients should be considered in patient education and diabetes management.