Authors: Frida Renström Robert W Koivula Tibor V Varga Göran Hallmans Hindrik Mulder Jose C Florez Frank B Hu Paul W Franks
Publish Date: 2015/02/24
Volume: 58, Issue: 5, Pages: 997-1005
Abstract
The association of single nucleotide polymorphisms SNPs proximal to CRY2 and MTNR1B with fasting glucose is well established CRY1/2 and MTNR1B encode proteins that regulate circadian rhythmicity and influence energy metabolism Here we tested whether season modified the relationship of these loci with blood glucose concentrationSNPs rs8192440 CRY1 rs11605924 CRY2 and rs10830963 MTNR1B were genotyped in a prospective cohort study from northern Sweden n = 16499 The number of hours of daylight exposure during the year ranged from 45 to 22 h daily Owing to the nonlinear distribution of daylight throughout the year season was dichotomised based on the vernal and autumnal equinoxes Effect modification was assessed using linear regression models fitted with a SNP × season interaction term marginal effect terms and putative confounding variables with fasting or 2 h glucose concentrations as outcomesThe rs8192440 CRY1 variant was only associated with fasting glucose among participants n = 2318 examined during the light season β = −004 mmol/l per A allele 95 CI −008 −001 p = 002 p interaction = 001 In addition to the established association with fasting glucose the rs11605924 CRY2 and rs10830963 MTNR1B loci were associated with 2 h glucose concentrations β = 007 mmol/l per A allele 95 CI 003 012 p = 00008 n = 9605 and β = −011 mmol/l per G allele 95 CI −015 −006 p 00001 n = 9517 respectively but only in participants examined during the dark season p interaction = 0006 and 004 respectively Repeated measures analyses including data collected 10 years after baseline n = 3500 confirmed the results for the CRY1 locus p interaction = 001
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