A measure of blood glucose control all too familiar to people with diabetes apparently fluctuates of its own accord throughout the year, researchers report.
With too much glucose in the blood, a certain amount of hemoglobin becomes “glycosylated,” and the percentage of glycosylated hemoglobin, or HbA1c, therefore reflects how well or poorly glucose levels are being kept under control over time.
However, monthly HbA1c levels wax and wane depending on the time of year, according to a report in the American Journal of Epidemiology.
As Dr. Chin-Lin Tseng told Reuters Health, “Our results confirm other studies regarding the seasonality of variation in A1c levels and showed that hemoglobin A1c values are higher during winter, especially in colder climates.”
Tseng, at the East Orange VA Medical Center, New Jersey, and colleagues studied monthly HbA1c levels over a 2-year period for more than 285,000 United States military veterans.
HbA1c levels averaged over a year were about 7.86 units, but varied by season. They were approximately 0.22 units higher in January to April compared with July to October, the researchers report, with values increasing in late autumn and decreasing in the spring.
Seasonal HbA1c patterns were similar for men and women, users and non-users of insulin, and for all races and ages.
Seasonal variations in HbA1c were most pronounced in areas having the lowest temperature extremes during the winter, the researchers note. In fact, there were no significant seasonal variations in areas with the lowest temperatures above 50 degrees Fahrenheit.
“The study demonstrated that the elevations of A1c are probably not related to holiday dietary indiscretion, but rather to colder ambient temperatures during winter,” Tseng pointed out.