Seasonal variations of insulin sensitivity from a euglycemic insulin clamp in elderly men

Abstract

Introduction. Seasonal variations in hemoglobin-A1c have been reported in diabetic patients, but the underlying mechanisms have not been elucidated.

Aims. To study if insulin sensitivity, insulin secretion, and fasting plasma glucose showed seasonal variations in a Swedish population-based cohort of elderly men.

Methods. Altogether 1117 men were investigated with a euglycemic insulin clamp and measurements of fasting plasma glucose and insulin secretion after an oral glucose tolerance test. Values were analyzed in linear regression models with an indicator variable for winter/summer season and outdoor temperature as predictors.

Results. During winter, insulin sensitivity (M/I, unit = 100 × mg × min^-1 × kg^-1/(mU × L^-1)) was 11.0% lower (4.84 versus 5.44, P = 0.0003), incremental area under the insulin curve was 16.4% higher (1167 versus 1003 mU/L, P = 0.007). Fasting plasma glucose was, however, not statistically significantly different (5.80 versus 5.71 mmol/L, P = 0.28) compared to the summer season. There was an association between outdoor temperature and M/I (0.57 units increase (95% CI 0.29–0.82, P < 0.0001) per 10°C increase of outdoor temperature) independent of winter/summer season. Adjustment for life-style factors, type 2 diabetes, and medication did not alter these results.

Conclusions. Insulin sensitivity showed seasonal variations with lower values during the winter and higher during the summer season. Inverse compensatory variations of insulin secretion resulted in only minor variations of fasting plasma glucose. Insulin sensitivity was associated with outdoor temperature. These phenomena should be further investigated in diabetic patients.

Key words::

• Insulin secretion
• insulin sensitivity
• seasonal variation

Acknowledgements

We thank the Uppsala Clinical Research Center (UCR), Uppsala, Sweden, employer of L.B. The study was supported by grants from the Family Ernfors, the Thuring, the Thuréus, the Åke Wiberg, and the Selander Foundations. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Results and views of the present study represent the authors and not necessarily any official views of the Medical Products Agency where Björn Zethelius is employed.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.