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.
