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.

Environmental effects of ambient temperature and relative humidity on insulin pharmacodynamics in adults with type 1 diabetes mellitus

“…Evidence from epidemiological research suggests seasonal differences in HbA1c and clinical onset of diabetes, with warmer temperatures (summer) favouring lower HbA1c and lower incidence of diabetes compared to cooler temperatures (winter). Conversely, there is a paucity of recent, well‐controlled experimental studies employing technological advancements, such as an environmental chamber, using the gold standard glucose clamp technique, to investigate the effects of ambient temperature on insulin action; such studies could provide evidence of a cause‐effect relationship. Nevertheless, there is increasing evidence of the local effects of temperature on insulin pharmacodynamics and pharmacokinetics.…”

Seasonality of Insulin Use in German Outpatients With Diabetes: A Retrospective Analysis

“…5 More recently, a Swedish analysis found a contradictory result, as insulin sensitivity was lower in winter than in summer. 6 Furthermore, the same study showed no significant association between fasting plasma glucose and seasonality. Interestingly, in line with the findings of Berglund and colleagues, 6 it has been suggested that 25-hydroxyvitamin D may decrease insulin resistance and may protect against the risk of developing T2DM.…”

“…6 Furthermore, the same study showed no significant association between fasting plasma glucose and seasonality. Interestingly, in line with the findings of Berglund and colleagues, 6 it has been suggested that 25-hydroxyvitamin D may decrease insulin resistance and may protect against the risk of developing T2DM. 7 However, even though these results are of great interest, little is known about the impact of seasons on the insulin needs of patients affected by diabetes.…”

“…More recently, in 2011, Berglund and colleagues, in a Swedish study including more than 1100 elderly patients, examined seasonal variations of insulin sensitivity, insulin secretion, and fasting plasma glucose. 6 Insulin sensitivity was found to be 11% lower-and the incremental area under the insulin curve 16% higher-in winter than in summer, even if fasting plasma glucose did not significantly differ between the two seasons. Moreover, it was estimated in the same population-based cohort of older people that outdoor temperature was positively associated with insulin sensitivity, with such relation being independent of the season.…”

“…Another important difference that could account for the discrepancy in the findings is that these two studies were performed in two different populations, as Berglund and colleagues included healthy elderly men who had not received insulin treatments, whereas the present analysis included only T1DM and T2DM patients followed in general practices in Germany. 6 The present study has several limitations, which should be mentioned. First, no valid information was provided on diabetes duration.…”