HbA(1c) levels in schoolchildren with type 1 diabetes are seasonally variable and dependent on weather conditions.

Abstract

Aims/hypothesisWe evaluated seasonal HbA1c changes in children with type 1 diabetes and its relation with measures of weather conditions.MethodsHbA1c changes over more than 3 years were evaluated in type 1 diabetic patients who were younger than 18 years and had diabetes duration of more than 12 months, and correlated with measures of weather conditions (ambient temperature, hours of sunshine and solar irradiance). After comparison of autocorrelation patterns, patterns of metabolic control and meteorological data were evaluated using Spearman rank correlation.ResultsA total of 3,935 HbA1c measurements in 589 school (≥7 years) and 88 preschool (<7 years) children were analysed. Mean (±SD) HbA1c level for the whole study period was 7.65 ± 1.12%. The lowest HbA1c levels were observed in late summer and the highest in winter months, with differences consistently exceeding 0.44%. Autocorrelation analysis of HbA1c levels in schoolchildren showed a sine-wave pattern with a cycle length of roughly 12 months, which mirrored changes in ambient temperature. Strong negative correlations of HbA1c with ambient temperature (R = −0.56; p = 0.0002), hours of sunshine (R = −0.52; p = 0.0007) and solar irradiance (R = −0.52; p = 0.0006) were present in schoolchildren, but not in preschoolers (p ≥ 0.29 for each correlation).Conclusions/interpretationSeasonal changes of HbA1c levels in schoolchildren with type 1 diabetes are a significant phenomenon and should be considered in patient education and diabetes management. They may potentially affect the results of clinical trials using HbA1c levels as their primary outcome, as well as HbA1c-based diagnosis of diabetes.Electronic supplementary materialThe online version of this article (doi:10.1007/s00125-010-2013-4) contains supplementary material, which is available to authorised users.