What factors influence TSH release?
TSH secretion is primarily related to circadian rhythm, Process-C, though there is SWH, Process-S, influence. TSH secretion in young healthy males shows an early evening circadian elevation before sleep onset, then a decline shortly after sleep onset continuing until it reaches a nadir in the afternoon. The inhibitory influence of sleep on TSH release is thought to occur during SWS. Therefore, clinicians may need to temper therapeutic decisions made on the basis of a sole mid-afternoon TSH value or an evening TSH level ordered in an emergency department. The highest TSH levels in the daytime, when outpatient laboratories are open, are after a person wakes up. With acute sleep loss, TSH takes its usual early-evening upturn at approximately 6 pm but, instead of the usual TSH downturn at sleep onset, with sleep deprivation TSH continues to rise to nearly twice the normal maximum through the middle of the usual sleep period. TSH hits a peak in the middle of the total sleep deprivation period, and from there, it begins a downward trajectory, eventually normalizing in the sleep-deprived individual’s day-time recovery sleep. Thus, a TSH value obtained at 7 am in such a patient reflects the influence of lack of sleep and probably does not reflect the need for thyroid hormone initiation or adjustment. The loss of an inhibitory effect of sleep on the circadian TSH elevation may contribute to elevated TSH values seen in acutely ill hospitalized patients.