liveonearth (liveonearth) wrote,

Thyroid marker (TSH) varies significantly on diurnal cycle

The gist of the new finding by Dr Schor is that many hypothyroid patients may be missed because up to now nobody has realized that TSH levels fluctate on a pattern not much different from cortisol. This is no surprise to me since I have already learned that when we awaken naturally in the morning, it coincides with an increase on our body temperature, whereas when we fall to sleep, our bodies cool down. Thyroid hormone is a heater upper; without it you are cold. Based on what I know of the release patterns of TSH (thyroid stimulating hormone), CRH (cortisol releasing hormone), and GH (growth hormone), I am going to assume that all hypothalamic hormones follow a diurnal rhythm, and that it is possible that they might all pulse in the pre-dawn hours and decrease in the afternoon.

Time of day makes a difference in thyroid testing, by Jacob Schor ND, August 14, 2012

TSH levels follow a circacian rhythm:
peak levels at 2-4am, lowest levels at 4-8pm
Extent of fluctuations greater than previously imagined
Afternoon samples lead to under diagnosis of hypothyroidism
(Not even counting the dispute about what ranges to be used.
Conventional: 0.5-5.0 mU/L.0)

Best time to collect: first thing in the morning
CV dz much more with TSH levels under 2.5.
REF: Duntas LH, Biondi B. New insights into subclinical hypothyroidism and cardiovascular risk. Semin Thromb Hemost. 2011 Feb;37(1):27-34. Epub 2011 Jan 19.

Federal Endocrinological Research Centre in Moscow
N = 20 women with subclinical hypothyroidism
Median morning TSH value for women with subclinical hypothyroidism was 5.83 mU/L.
Afternoon median was 3.79 mU/L.
REF: Sviridonova MA, Fadeyev VV, Sych YP, Melnichenko GA. Clinical Significance of TSH Circadian Variability in Patients with Hypothyroidism. Endocr Res. 2012 Aug 2.
Tags: circadian, cortisol, growth hormone, hormones, hypothalamus, labs, medicine, thyroid

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