Authors: Berglund, Lars¹; Berne, Christian²; Svärdsudd, Kurt³; Garmo, Hans⁴; Melhus, Håkan²; Zethelius, Björn¹

Source: Upsala Journal of Medical Sciences, Volume 117, Number 1, March 2012 , pp. 35-40(6)

Publisher: Informa Healthcare

Abstract:

<title>Abstract</title>

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.

Keywords: Insulin secretion; insulin sensitivity; seasonal variation

Document Type: Research article

DOI: http://dx.doi.org/10.3109/03009734.2011.628422

Affiliations: 1: 1 Department of Public Health/Geriatrics, Uppsala University, Uppsala, Sweden 2: 2 Department of Medical Sciences, Uppsala University, Uppsala, Sweden 3: 3 Department of Public Health/Family Medicine and Clinical Epidemiology Uppsala University, Uppsala, Sweden 4: 4 Uppsala Clinical Research Center, University Hospital, Uppsala, Sweden

Publication date: 2012-03-01

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