Seasonal fluctuations of glycated hemoglobin levels in Japanese diabetic patients

Abstract 

Aims

We examined whether glycated hemoglobin (HbA_1C) levels of Japanese diabetic patients showed seasonal fluctuations.

Methods

Subjects included 2511 diabetic patients who regularly visited a single diabetic outpatient clinic for 10 years. A total of 253,477 HbA_1C measurements, as well as sex, age, BMI, type of diabetes, and mode of therapy were extracted from a hospital-based database. For the cross-sectional and longitudinal analyses, average monthly HbA_1C values of subjects and amplitudes of seasonal fluctuations were calculated. For the time-series analysis, seasonal adjustment factors of each subject were classified as complete, incomplete, or no fluctuation.

Results

Subjects showed a clear seasonal fluctuation of HbA_1C levels, with highest levels in March (7.69%) and lowest levels in August (7.46%; p<0.001). The amplitudes of the seasonal fluctuations were associated with the mean HbA_1C levels. The time-series analysis showed that 78.3% of patients had complete or incomplete seasonal fluctuations. HbA_1C levels were highest in winter–spring and lowest in summer–autumn in most patients; however, some patients showed a reverse pattern.

Conclusions

Seasonal fluctuations of HbA_1C levels were recognized in most of the Japanese diabetic patients. Physiological or metabolic factors related to temperature may be the main cause of seasonal fluctuations in HbA_1C levels.

Abbreviations: OHAs, oral hypoglycemic agents, SAF, seasonal adjustment factor

Keywords: HbA_1C, Seasonal fluctuation, Hospital-based database