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One measure of blood glucose levels, hemoglobin A1C, seems to vary with the seasons, researchers say: Monthly levels are higher during the winter, especially in colder climates.


Researchers studied monthly A1C levels in more than 285,000 U.S. military veterans during a 2-year period. Average yearly levels of A1C were 7.86 units. Levels were about 0.22 units higher from January to April than from July to October. Values increased in late fall and decreased in the spring. The seasonal changes in A1C were similar regardless of gender, insulin use, age, or race.


Areas with the lowest temperatures during the winter had greater variation in A1C levels. Seasonal changes in levels didn't occur in areas where the lowest yearly temperatures stayed above 50[degrees] F. Researchers say the data indicate that increased levels of A1C during the winter probably aren't related to holiday eating sprees.




Seasonal patterns in monthly hemoglobin A1c values, American Journal of Epidemiology, C Tseng, et al., March 15, 2005.