Glycated hemoglobin (HbA1c) levels in diabetes patients may vary according to the season, suggest results from a Japanese study.
Previous research has reported a seasonal fluctuation in HbA1c levels, but most of these studies have been small and of short duration, say researchers.
In this study, Hiroshi Sakura (Tokyo Women’s Medical University, Shinjuku-ku) and colleagues collected data on 2511 diabetic patients who regularly attended a diabetes outpatient clinic in Tokyo over a 10-year period.
The team analyzed a total of 253,477 HbA1c measurements, allowing average monthly values and amplitudes of seasonal fluctuations to be calculated for the participants. Other factors such as gender, age, body mass index, type of diabetes, and mode of therapy were also recorded.
As reported in the journal Diabetes Research and Clinical Practice, the investigators found that there was a clear and significant fluctuation in seasonal HbA1c levels with the highest levels recorded in March at 7.69% and the lowest in August at 7.46%.
Further analysis showed that 78.3% of patients had at least some seasonal variation in HbA1c concentration. Women, young, or obese individuals, Type 1 diabetics, and those treated with insulin or oral antidiabetes drugs had the largest seasonal fluctuations.
Most patients had higher levels of HbA1c in winter-spring than in summer-autumn, but some individuals did demonstrate the reverse pattern.
Sakura et al say: “Although the precise mechanisms of these fluctuations are unclear, certain physiological or metabolic factors related to temperature, as well as seasonal variations in diet, exercise, or social customs may cause seasonal fluctuations in HbA1C levels.”
They conclude: “In many patients, particularly those with poor glycemic control, the amplitudes of fluctuation exceed 0.5% and may be responsible for the development of microvascular and macrovascular complications.
“Therefore, we should take seasonal fluctuations of glycemic control into consideration in the treatment of diabetes.”