A study published in the Journal of Clinical Endocrinology and Metabolism found that significant physiologic stress inhibits the transport of the (inactive) T4 thyroid hormone into the cell while non-physiological stress had no effect. Serum T4 levels were artificially elevated in physiologically stressed individuals which confirms that serum T4 and TSH levels are poor markers for tissue thyroid levels in stressed individuals (1).
One study found that with significant physiological stress, tissue levels of T4 and T3 were dramatically reduced by up to 79% without an increase in TSH. T4 and T3 levels in different tissues in different individuals showed a significant variation which was not reflected by TSH or serum T4 and T3 levels. This explains the wide range of symptoms that are due to tissue specific hypothyroidism not reflected or detected by standard blood tests, including TSH and T4 (2).
A confirming study published in the Journal of Clinical Endocrinology and Metabolism has shown that the free T3/reverse T3 ratio was the most accurate marker for reduced cellular uptake of T4 (3).
A number of substances have been identified that are produced in response to physiologic stress or calorie reduction. These include billirubin and fatty acids and can results in a 27%-42% reduction in cellular uptake of T4 but has no effect on T4 or T3 uptake into the pituitary (4,5,6,7,8) (see thyroid transport graph).
What does this mean for you?
If you are stressed, you enter a state of hypothyroidism which cannot be detected by routine NHS blood tests. Typical symptoms are fatigue, tiredness, weight gain.
What you can do about it?
It is important to get your stress under control. Our complementary therapists can help you with this. You might also want to have an in-depth thyroid laboratory test as you could benefit from (temporary) thyroid replacement medication with Nature-Thyroid.
References:
- Sarne DH, Refetoff S. Measurement of thyroxine uptake from serum by cultured human hepatocytes as an index of thyroid status: Reduced thyroxine uptake from serum of patients with nonthyroidal illness. J Clin Endocrinol Metab 1985;61:1046–52.
- Arem R, Wiener GJ, Kaplan SG, Kim HS, et al. Reduced tissue thyroid hormone levels in fatal illness. Metabolism 1993;42(9):1102-8.
- Vos RA, de Jong M, Bernard BF, et al. Impaired thyroxine and 3,5,3′-triiodothyronine handling by rat hepatocytes in the presence of serum of patients with nonthyroidal illness. J Clin Endocrinol Metab 1995;80:2364-2370.
- Everts ME, De Jong M, Lim CF, Docter R, et al. Different regulation of thyroid hormone transport in liver and pituitary: Is possible role in the maintenance of low T3 production during nonthyroidal illness and fasting in man. Thyroid 1996;6(4):359-368
- Everts ME, Docter R, Moerings EP, van Koetsveld PM, Visser TJ, et al. Uptake of thyroxine in cultured anterior pituitary cells of euthyroid rats. Endocrinology 1994;134:2490–2497.
- Lim C-F, Bernard BF, De Jong M, et al. A furan fatty acid and indoxyl sulfate are the putative inhibitors of thyroxine hepatocyte transport in uremia. J Clin Endocrinol Metab 1993;76:318-324.
- Lim C-F, Docter R, Visser TJ, Krenning EP, Bernard B, et al. Inhibition of thyroxine transport into cultured rat hepatocytes by serum of non-uremic critically ill patients: Effects of bilirubin and nonesterified fatty acids. J Clin Endocrinol Metab 1993;76:1165-1172.
- Everts ME, Lim C-F, Moerings EPCM, Docter R, et al. Effects of a furan fatty acid and indoxyl sulfate on thyroid hormone uptake in cultured anterior pituitary cells. Am J Physiol 1995;268:E974-E979.
Source: https://www.nahypothyroidism.org/thyroid-hormone-transport/