Annual change in insulin sensitivity

The incidence of both type 2 diabetes and cardiac events is reported to be higher during winter, indicating a putative annual periodic change in insulin sensitivity (IS). Annual differences in IS quantified as HOMA-%S and Matsuda-Sensitivity Index - were analyzed using a cosine wave-fitting algorithm in a cross-sectional study group including 2 385 participants. Additionally, semiannual differences in IS were compared. We found periodicity for HOMA-%S and Matsuda-Sensitivity Index (p = 0.02 or 0.006), which was strengthened after restriction to participants without diabetes ( p = 0.009 or 0.004). The rhythm amplitude of 0.08 indicated moderate changes in IS throughout the year. IS was significantly higher when participants were enrolled during the second vs. the first half of the year (HOMA-%S 112.0 +/- 3.0 % vs. 97.4 +/- 2.4 %, p < 0.001). The impact of the half-year on IS, which remained significant after adjustment for confounders, was again moderate and explained only 0.5% of the variation. IS showed a significant moderate annual periodicity, which may affect the interpretation of studies reporting small changes in IS