Do your A1C levels rise every winter? You’re not alone.
A team of researchers working in Veterans Health Administration centers across the country has found a link between cold weather and higher A1C levels. (A1C tests provide a snapshot of blood glucose control over 3 months.) For 2 years, the group studied 272,722 veterans with diabetes. The A1C levels of those in the study group were averaged and analyzed by climate and season.
After considering other factors that could affect A1C levels, such as age, sex, race, and severity of diabetes, the researchers found an independent seasonal pattern linked to colder temperatures. In all climates, A1C levels peaked from February through April; they hit their lowest points in August through September. The average increase in A1C levels from summer to winter was 0.22 percentage points.
The people who experienced the most fluctuation in terms of their A1C levels were those who lived in what the researchers called “intermediate” climates- places where winter temperatures ranged from 32° F to 40° F.
Interestingly, people who lived in the coldest areas- places where winter temperatures ranged from 5° F to 32° F- experienced a little less fluctuation in terms of their A1C levels. The researchers don’t know why this is, but they speculate that perhaps people with diabetes who live in very cold regions don’t go outside as much in the winter. By staying inside, they would have less exposure to the effects of the cold.
The authors still aren’t sure how cold triggers a rise of A1C levels, but they suspect it may be the same unknown physical response to cold that also causes blood pressure and heart rate to rise. Previous studies have shown that cardiovascular events and strokes follow a similar seasonal pattern. These patterns could influence how diabetes control is maintained. More study is needed, the authors say. This study was published in the American Journal of Epidemiology in March 2005.