TOTAL SLEEP-DEPRIVATION AND THE THYROID AXIS - EFFECTS OF SLEEP AND WAKING ACTIVITY

Background: Circadian and sleep components modulate anterior pituitary release of thyrotropin (TSH), the chemical substance regulating the t hyroid hormones, thyroxine (T-4), and triiodothyronine (T-3). The pres ent study examined TSH, T-4, and T-3 concentrations across the wake-sl eep boundary time (2300-0130 hours) before, during, and after a 64-h s leep deprivation paradigm. Additionally, adrenocorticotropic hormone ( ACTH) and cortisol were measured as an index of hypothalamic-pituitary -adrenal axis activation. Activity levels and ratings of effort requir ed to perform cognitive tasks were also incorporated to evaluate physi cal and cognitive load, respectively, across the study period. Assessi ng the combined effects of activity and sleep deprivation on thyroid h ormone economy is relevant to the relationship of high physical and/or cognitive performance demands during sleep deprivation inherent in ex tended military operations and space exploration. Method: There were 1 2 healthy subjects who were monitored during a 2-d baseline period, 3 d of total sleep deprivation, and 2 nights of recovery sleep. Serum sa mples were collected at 2300 hours and 0130 hours across the entire st udy period, and measured for TSH, T-4, T-3, and glucocorticoids. Resul ts: Change scores evaluated at the wake-sleep boundary time demonstrat ed significant inhibitory effects of sleep on thyroid hormone measures . As expected, sleep deprivation was associated with elevated TSH. How ever, sleep deprivation also significantly increased circulating level s of T-3 at 2300 hours and T-4 concentration change scores (2300-0130 hours). Glucocorticoid levels did not track thyroid hormone changes. P hysical activity remained constant while subjective ratings of effort to perform cognitive tasks increased significantly during sleep depriv ation. Conclusion: Compared to sleep deprivation studies under constan t conditions reporting no change in peripheral T-4 and T-3 levels, the present study suggests activity level, including cognitive effort to perform, during total sleep deprivation may produce substantive change s in the thyroid axis.