What is functional hypothyroidism?

You won’t find the term functional hypothyroidism in the medical literature, or at least not yet. Primarily due to clinical hypothyroidism being bound to a rigid assessment usually diagnosed by the blood test thyroid stimulating hormone or TSH.

TSH secretion is controlled by synthesis of thyroid releasing hormone or TRH in the supraortic and supraventricular nuclei of the hypothalamus. TRH is transported to the anterior pituitary by the hypothalamo- hypophysial portal system where it stimulates synthesis of TSH. T4, T3 and TRH control the secretion of TSH (Gardner et al., 2011).

TSH production can also be affected by TSH receptor damage, medical drugs, disease states, iodide, blood glucose levels and other circulating hormones TSH may also be affected by environmental pollutants and heavy metals (Llop et al., 2015).  Metabolic disease and increases in Body Mass Index appear to be correlated with an increase in TSH levels (Ruhla et al., 2010).

Often, you will see clear links and studies to key micronutrients such as zinc, selenium, iodine and other important co-factors. These deficiencies can exist demographically but usually in westernised societies, there deficiency can be linked to impaired absorption rates, perhaps linked to digestive dysfunction and other factors.

“Measuring the amount of thyroid in the blood isn’t a good way to evaluate adequacy of thyroid function, since the response of tissues to the hormone can be suppressed (for example, by unsaturated fats) (Peat, R.1999).

 Dietary factors such as unsaturated fatty acids in the diet may potentially be one of the most overlooked factors that supress thyroid function. Other factors such as caloric restriction, stressful environments, over exercising and other factors are some of the others. It’s well known that in certain areas of hormone dysregulation such as menstrual cycle irregularities, oligoamenorrohea (loss of cycle), anovulation (failure to ovulate) and lack of libido and fertility in both men and women,  can be attributed to poor energy intake and environmental factors (Nieuwenhuijsen et al., 2014) (Skakkebæk, 2003). Dietary factors have synergy with hormonal imbalances perpetuating high levels of estrogen.

The functional suppression of thyroid function by unsaturated fats, eating a so-called healthy diet (full of uncooked brassica vegetables, nuts and seeds) orthorexic states and other factors is largely ignored by physicians.

I can say with some certainty, after completing postgraduate studies at university with a number of Doctors, that diet and inhibitory factors of diet rarely get assessed when it comes to assessing energy and thyroid function.

A persistent functional hypothyroid state, induced by unsaturated fats may lead to the pre-diabetic and diabetic states induced by an inability to utilise carbohydrate and the preferential shift to use of fats instead of sugars as suggested in the Randle or glucose fatty acid cycle (Randle, Garland, Hales, & Newsholme, 1963). Increased cortisol, oxidation, decreased carbon dioxide and an increased stress on the oxidative system, could potentially lead to glycolysis and an increase in lactic acid, further increasing damage, stress and further suppression of thyroid function.

Measurement of thyroid blood tests remains inaccurate and problematic without the inclusion of a variety of symptoms and previously accurate assessment, such as basal metabolic rate, body temperature and pulse. The suppression of both thyroid and adequate energy states will always remain.

As the common approach for diagnosing hypothyroidism is having TSH above 4 or 5 mmUL and the preferred treatment is to supplement with synthetic levothyroxine. How much change can you realistically achieve if you fail to address the supressed metabolism induced by diet, an individuals susceptibility to stress and their own environment?



Gardner, D. G., Shoback, D. M., Greenspan, F. S. et al .(2011). Greenspan’s Basic and Clinical Endocrinology. McGraw Hill.

Llop, S., Lopez-Espinosa, M. J., Murcia, M., Alvarez-Pedrerol, M., Vioque, J., Aguinagalde, X., … Ballester, F. (2015). Synergism between exposure to mercury and use of iodine supplements on thyroid hormones in pregnant women. Environmental Research, 138, 298–305. http://doi.org/10.1016/j.envres.2015.02.026

Nieuwenhuijsen, M. J., Basagana, X., Dadvand, P., Martinez, D., Cirach, M., Beelen, R., & Jacquemin, B. (2014). Air pollution and human fertility rates. Environment International, 70, 9–14. http://doi.org/10.1016/j.envint.2014.05.005; 10.1016/j.envint.2014.05.005

Peat, R. (1999). Thyroid Therapies, Confusion and Fraud. Retrieved from www.raypeat.com/articles/articles/thyroid.shtml

Randle, P. J., Garland, P. B., Hales, C. N., & Newsholme, E. A. (1963). The glucose fatty-acid cycle its role in insulin sensitivity and the metabolic disturbances of diabetes mellitus. The Lancet, 281(7285), 785–789. http://doi.org/10.1016/S0140-6736(63)91500-9

Ruhla, S., Weickert, M. O., Arafat, A. M., Osterhoff, M., Isken, F., Spranger, J., … Möhlig, M. (2010). A high normal TSH is associated with the metabolic syndrome. Clinical Endocrinology, 72(5), 696–701. http://doi.org/10.1111/j.1365-2265.2009.03698.x

Skakkebæk, N. E. (2003). Testicular dysgenesis syndrome. In Hormone Research (Vol. 60, p. 49). http://doi.org/10.1159/000074499