0196 One Less Pathway to Explain the Chronic Insufficient Sleep and Metabolism Relationship: Thyroid Regulation

Abstract Introduction Chronic insufficient sleep contributes to the development of obesity and type 2 diabetes (T2D). However, the physiologic underpinnings of these effects are incompletely understood. There is some evidence that sleep restriction (SR) adversely affects thyroid hormones and growth factors involved in energy metabolism, but findings are mixed. Furthermore, no study has evaluated changes in thyrotropic axis hormones in response to a model of chronic, mildly insufficient sleep resembling real-world short sleep. Therefore, we investigated whether 6wk of 1.5 h/night SR vs. maintenance of adequate sleep (AS) impacted free thyroxine (T4), thyroid stimulating hormone (TSH), and fibroblast growth factor-21 (FGF21) in healthy adults. Methods Men and women with actigraphy-assessed habitual total sleep time (TST) of 7-9h/night and no cardiometabolic diseases participated in a randomized, crossover study with two 6-week phases: AS and SR. Sleep was monitored daily with actigraphy, and compliance was assessed every 1-2wk. Blood was collected following a ≥12h fast at baseline, wk 3, wk 4, and endpoint of each phase. For this investigation, circulating levels of T4, TSH, and FGF21, within an all-female subsample (n=18), were quantified from plasma. Linear mixed models tested the effect of SR on the post-baseline values of the outcomes, with models adjusted for corresponding baseline outcome values, week, and phase. Results Data were available from 30 participants (20 women, 39.0±14.0y, BMI: 26.7±3.6; 10 men, 29.4±5.2y, BMI: 26.6±2.2). T4, TSH, and FGF21 concentrations at the baselines of each phase ranged from 0.27-2.55 ng/dL (M±SD: 0.87±0.47), 0.86-1.66 μIU/ml (M±SD: 1.24±0.19) and 17.5-383.3 pg/mL (M±SD: 140.2±97.6), respectively. In the full sample free T4 (β=-0.02, p=0.64) and TSH (β=0.02, p=0.67), and in the subsample, FGF21 (β=-1.57, p=0.83) were not significantly different between study arms. In analyses of T4 and TSH stratified by sex, there were no differences between study arm. Conclusion In a sample of healthy adults, prolonged mild sleep restriction did not cause alterations in thyroid hormones and FGF21. These findings suggest that adverse endocrine and metabolic consequences commonly observed with chronic short sleep are not owed to disruptions in the thyroid axis endocrine pathway. Support (if any) American Heart Association 16SFRN27950012 and NIH/NHLBI R01HL128226 and R35HL155670 and in part by UL1TR001873