Seasonal Variation in Glycated Hemoglobin in Type 2 Diabetes Patients on Semi-Arid Climate Between the Years 2005-2015

Background: Diabetes mellitus type 2 is one of the most common chronic diseases around the world with increasing prevalence every year.

Many studies have shown that optimal balancing of the glycated hemoglobin (HbA1c) is one of major factors in preventing complications.

Seasonal variations in the level of HbA1c have already been described in several geographical areas around the world, but not in semi-arid climates, where there is a high diurnal and seasonal variation in temperatures.

Aim: The purpose of our study was to investigate the seasonal variations of HbA1c values in a very compliant community-based population over a period of 10 years in semi-arid climate.

Methods: The retrospective cohort study included 61,187 HbA1c values from 2860 patients. We calculated the seasonally and monthly average of HbA1c values of the overall population and for sub populations defined by age, gender, BMI, ethnic group, insulin use, smoking status and region of residence, matched to the mean temperature and diurnal range over the 30 days prior to the HbA1c blood test.

Results: We found a sinusoidal seasonal pattern with statistically significant HbA1c differences between the spring peak and the autumn nadir (F=18.4, P<0.001). HbA1c exhibited its highest values in March to May, and its lowest values in October-November, with a difference of 0.17%-0.31% depending on the subgroups. Linear and quartile models were conducted. There were significant seasonal and meteorological effects on the HbA1c results. Division into subgroups shows the different effects of mean temperature on HbA1c depending on gender, age, ethnicity and smoking habits.

Conclusion: The study identifies particular subgroups in which the seasonal influence is particularly marked, and suggests possible reasons for this, such as higher exposure to outdoor weather conditions.

Recognition of the influence of different seasons on HbA1c levels in this geographical region could help physicians with HbA1c balancing