Circadian clocks and the thyroid.

Circadian clocks run the thyroid axis and are present in thyroid cells.
The thyroid axis clock Is regulated by scn, supra chiasmatic nucleus, in the hypothalamus. TRH from hypothalamus stimulates pituitary release of TSH. TSH peaks at 2-4 am and t3 release by the thyroid lags one hour later, thyroid hormone receptors and other thyroid activators are sensitive to the periodicty of the clock. The thyroid clock are present in primary thyrocytes ( thyroid cells). The clock is indispensable for cell cycle progression. One of the clock’s circadian genes is called Period 2. Interestingly, Period 2 is also a tumor suppressor gene. Tumor supressor genes work to prevent tumor or cancer growth. It is not clear if the clock changes before thyroid cancer occurs or if cancer leads to the thyroid clock changing. What we do know is that benign thyroid nodules retain a normal clock function. In contrast, thyroid nodules that are cancers lose circadian periodicity, suggesting that the protective tumor supressing effect of the period 2 gene is lost in the setting of thyroid cancer.
One other implication of the thyroid axis clock is that it matters when your thyroid tests are measured. It is best to measure them in the morning, when you have peak function, and to measure subsequent tests at the same time to truly know the exact value in the body. Measurements in the afternoon or night may lead to misinterpretation of your situation. This advice may not apply to chronic night shift workers.

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