functional hypothyroidism

Sub Clinical Hypothyroidism

Strange, must-try exotic fruits!.jpg

I’ve seen a number of assumptions from doctors suggesting that there’s no optimal diet for improving thyroid function. If that were the case there would be no optimal diet for heart disease, cancer or autoimmune disease but there are many proposed guidelines of certain foods that should be avoided.

 If you want to slow down the thyroid eating plenty of cruciferous vegetables, fish oils and exposure to oestrogens (environmental pollution, contraception and other medical drugs) seems to inhibit thyroid function dramatically and large amounts of anti-thyroid (goitregens) foods are certainly linked with thyroid cancer. Often an individual’s perceived healthy choices can suppress thyroid function and therefore be resolved with nutrition alone. A functionally suppressed thyroid state that’s treated with thyroid hormone may not yield the best results.

 Sub clinical hypothyroidism (SCH) is an issue that divides endocrinology but when you look at the process of thyroid dysfunction there are some clear indicators that should suggest that it’s treatment would be the most sensible (but not the most money making) action in the long run. Let’s start with defining what SCH is.

SCH is usually defined as an asymptomatic state in which free T4 is normal but TSH (thyroid stimulating hormone or TSH is the pituitary stimulator of thyroid hormone) is elevated. If serum TSH is >10mU/L there is consensus that the patient should be treated with thyroxine because of the likelihood that the patient will develop overt hypothyroidism with subnormal T4 and because this degree of SCH predisposes to cardiovascular disease. When the TSH is in the range of 4.5 to 10 mU/L, there is controversy about the efficacy of T4 therapy (Lavin, N, Ali, Omar., Beall, M.U., Bhutto, 2016).

Although many people with most forms of thyroid disease often present with diverse symptoms due to the systemic effects of thyroid hormone action but are often ignored through reductionist observation. The table below lists most of the major actions of thyroid function and deficits created by a hypothyroid state.


Thyroid hormone is necessary for all aspects of organised biology.

Thyroid hormone is necessary for all aspects of organised biology.

Here’s a short history of some of the contrasting opinions on treating SCH. Biondi cites the original controversies of Wartofsky and Dickey (2005) who favoured a narrower TSH range (Wartofsky & Dickey, 2005), which was in contrast to the opposition to a lower TSH suggested by Surks et al. (2005) (Biondi, 2013).

 The latter authors stated ‘that there was little evidence supporting the treatment of SCH, citing a single small study by Kong et al. treating 40 women with SCH (Kong et al., 2002).  The main findings demonstrated that thyroxine treatment had no impact on lipids, energy expenditure, weight gain or composition despite decreases in TSH levels in the treatment group (8.0 +- 1.5 mU/L change from baseline -4.6 +-2.3 mU/mL compared to 7.3 +- 1.6  -1.7 +-2.0 mU/L in the placebo). However this study, perhaps like many others (Laurberg et al., 2011) (Surks et al., 2005), failed to assess the nutritional status of this small group of patients. For example, if calorific excess were present, these markers may show little change, as weight loss requires a calorie deficit.  Conversely if a patient were chronically undernourished through a low nutrient intake, attempting to enhance metabolic rate and weight loss with TH replacement may be negated when adrenaline, glucagon and cortisol are produced to regulate blood sugar levels.

 Problems associated with some of the smaller seemingly positive older studies, is often the lack of control groups for comparison. A smaller RCT (treatment n-22 control n-19) comparing treatment of subjects with biochemically euthyroid TFTs  yet clinical hypothyroidism with thyroxine, found the intervention no more successful than placebo (Pollock et al., 2001). Whilst the effect of placebo cannot be discounted, the study only focused on cognitive function and wellbeing, factors that are a limited component of thyroid function.  A friend of mine also pointed out that the use of T4 alone and female cohort with an increased weight some 20kgs over the control group are also problematic issues in studies like this.

 More studies trickle through that builds upon previous suggestions that measuring TSH is a poor way to accurately assess thyroid function, primarily due to the facts that stress, environmental pollutants and nutrition can cause biochemistry and in particular thyroid blood tests to present as normal. The problem with ignoring SCH is the following scenario.

 You have isolated or a number of hypothyroid symptoms such as weight gain, high blood pressure, high cholesterol, hair loss, fatigue, low libido, altered menstrual cycle, anxiety or depression, poor sleep, constipation, brain fog, inflammation of the brain, altered heart contraction, dry skin etc.

 Good news Mrs X you have normal thyroid function as your blood tests came back within the normal ranges. The symptom/s you have must be in your head. Here you have high blood pressure take this anti-hypertensive medication.

The pituitary should be considered a source of evaluation that could be useful but should be treated with suspicion. There are many factors that alter thyroid feedback which include the disparity between the enzymes in the pituitary (deioidinase 2 supports the conversion of thyroid hormone in the pituitary and can appear normal)  and other tissues, thyroid receptor and mitochondrial damage. Recent meta analysis and other studies support the role of treating SCH to prevent cardiovascular disease, high cholesterol, hypertension (Ochs et al., 2008)(van Tienhoven-Wind & Dullaart, 2015)(Udovcic, Pena, Patham, Tabatabai, & Kansara, 2017) (Sun et al., 2017) and there’s a strong possibility that hypothyroidism in the central nervous system in areas like the prefrontal cortex are associated with dementia and Alzheimer’s (Pasqualetti, Pagano, Rengo, Ferrara, & Monzani, 2015)(Davis et al., 2008).

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Temperature, pulse and symptoms can be a useful indicator of function when bloods appear to support the notion of sub clinical hypothyroidism

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 It’s worth suggesting that endocrinologists should be well aware of all of the factors that can create the perception of normal blood tests, especially when individual’s present with clinical findings of hypothyroidism as suggested above. My previous posts on assessing thyroid function through body temperature and Ray Peat’s well written post should also be considered an integral part of assessment of thyroid evaluation. The concept of SCH is really only related to the blood test, because the other findings should give the game away.  Treating SCH shouldn’t be problematic when a thorough understanding of nutrition and environmental stimulus are known, and the only people at risk from taking a gradually increased dose of thryroxine would be individuals at risk of an immediate heart attack who generally would  present with a certain set of symptoms.

If Broda Barnes, an MD in the last century found that his patients didn’t succumb to heart disease when taking thyroid hormone. Shouldn’t we be looking for the more global implications of health improvements? Rather than treat high cholesterol, blood pressure, blood sugar, menstrual irregularities, metabolic syndrome (and many others) which all have a substantial relationship with thyroid function, with many studies that show substantial improvements when treated with thyroxine. Call me a cynic but perhaps a more detailed understanding of nutrition, environmental pollutants and their effects on thyroid physiology is probably more challenging to integrate into practice than completing genetic analysis with the proposed mutation driving a specific dysfunction.

 

References: 

BARNES, B. O. (1973). On the Genesis of Atherosclerosis. Journal of the American Geriatrics Society. http://doi.org/10.1111/j.1532-5415.1973.tb01239.x

Biondi, B. (2013). The normal TSH reference range: What has changed in the last decade? Journal of Clinical Endocrinology and Metabolism. http://doi.org/10.1210/jc.2013-2760

Davis, J. D., Podolanczuk, A., Donahue, J. E., Stopa, E., Hennessey, J. V, Luo, L. G., … Stern, R. A. (2008). Thyroid hormone levels in the prefrontal cortex of post-mortem brains of Alzheimer’s disease patients. Curr Aging Sci.

Kong, W. M., Sheikh, M. H., Lumb, P. J., Freedman, D. B., Crook, M., Doré, C. J., & Finer, N. (2002). A 6-month randomized trial of thyroxine treatment in women with mild subclinical hypothyroidism. American Journal of Medicine. http://doi.org/10.1016/S0002-9343(02)01022-7

Laurberg, P., Andersen, S., Carlé, A., Karmisholt, J., Knudsen, N., & Pedersen, I. B. (2011). The TSH upper reference limit: where are we at? Nature Reviews Endocrinology, 7(4), 232–239. http://doi.org/10.1038/nrendo.2011.13

Lavin, N, Ali, Omar., Beall, M.U., Bhutto, A. et al. (2016). Manual of Endocrinology and Metabolism (4th Editio). Lippincott Williams and Wilkins.

Ochs, N., Auer, R., Bauer, D. C., Nanchen, D., Gussekloo, J., Cornuz, J., & Rodondi, N. (2008). Meta-analysis: subclinical thyroid dysfunction and the risk for coronary heart disease and mortality. Annals of Internal Medicine, 148(11), 832–845.

Pasqualetti, G., Pagano, G., Rengo, G., Ferrara, N., & Monzani, F. (2015). Subclinical Hypothyroidism and Cognitive Impairment: Systematic Review and Meta-Analysis. The Journal of Clinical Endocrinology & Metabolism, 100(11), 4240–4248. http://doi.org/10.1210/jc.2015-2046

Pollock, M. A., Sturrock, A., Marshall, K., Davidson, K. M., Kelly, C. J., McMahon, A. D., & McLaren, E. H. (2001). Thyroxine treatment in patients with symptoms of hypothyroidism but thyroid function tests within the reference range: randomised double blind placebo controlled crossover trial. BMJ (Clinical Research Ed.). http://doi.org/10.1371/journal.pone.0098254

Sun, J., Yao, L., Fang, Y., Yang, R., Chen, Y., Yang, K., & Limin, T. (2017). The relationship between subclinical thyroid dysfunction and the risk of cardiovascular outcomes: a systematic review and meta-analysis of prospective cohort studies. International Journal of Endocrinology, 2017(2017). http://doi.org/10.1007/s00774-017-0828-5

Surks, M. I., Goswami, G., & Daniels, G. H. (2005). The thyrotropin reference range should remain unchanged. Journal of Clinical Endocrinology and Metabolism, 90(9), 5489–5496. http://doi.org/10.1210/jc.2005-0170

Udovcic, M., Pena, R. H., Patham, B., Tabatabai, L., & Kansara, A. (2017). Hypothyroidism and the Heart. Methodist DeBakey Cardiovascular Journal, 13(2), 55–59. http://doi.org/10.14797/mdcj-13-2-55

van Tienhoven-Wind, L. J. N., & Dullaart, R. P. F. (2015). Low-normal thyroid function and the pathogenesis of common cardio-metabolic disorders. European Journal of Clinical Investigation. http://doi.org/10.1111/eci.12423

Wartofsky, L., & Dickey, R. A. (2005). The evidence for a narrower thyrotropin reference range is compelling. Journal of Clinical Endocrinology and Metabolism. http://doi.org/10.1210/jc.2005-0455

A biochemical approach to decreasing muscle pain with food and hormones.

pain and hormones

pain and hormones

A biochemical approach to decreasing muscle pain is often the last place most people look and that includes many pain specialists. Modulating pain and hormones through food and other variables can create some impressive results. Aches and pains are a common theme in every day living. Some people seek to push themselves harder with excessive training schedules, others spend more time in a seated position and other factors contribute to tissue not responding the way that it should. Pain and the concept of nociception is a system of feedback for the body that is protective in essence. You touch something you shouldn’t; first pain kicks in to remove you from the painful stimulus (lasts less than 0.1 seconds), after that and depending on severity of damage second pain kicks in.

First pain and second pain (both reside in the anterolateral system or ALS) utilise different chemical messengers and another factor for this form of feedback is that other nociceptive factors like touch, visual, auditory and other sensations of stress can be part of the problematic feedback if not resolved. All of these have the capacity to interrupt optimal motor control and functioning of joints and soft tissues and affect hormone profiles. Even a bad smell can create neurological chaos.

Another less well known aspect (in therapy based settings) of disruptive function in muscle tissue are the effects of hormones that may lead to decreased feed back and be responsible for pain. Hypothyroidism affects muscle tissue via energy and neurological deficiencies.

Hypothyroidism results in

Slower peripheral and central nerve conduction velocity Lower body temperature is a factor creating slowed velocity Decreased active cell transport in the cerebral cortex Decreased flux of sodium and calcium for contraction/relaxation Poor production of energy for contraction/relaxation Decreases depolarisation of action potential

cold body

cold body

In a nutshell a colder, slower body leads to a decreased   coordinated body that has a hard time contracting and relaxing muscle tissue. This can lead to increased incidence of injury and pain.

A slowed heart rate is a sign of hypothyroidism and the bradychardia (slowed heart rate) should serve the purpose of describing the decreased rate of function throughout all muscle tissue. Thyroid hormone can improve both rate of contraction and relaxation in both fast and slow twitch muscles but also exerts a cardio protective role on blood vessels and bowel function via smooth muscle tissue. The documented symptoms of hypertension and constipation along with the neuromuscular actions tend to resolve with adequate thyroid hormone (Gao, Zhang, Zhang, Yang, & Chen, 2013).

Prior to initiating thyroid therapy it’s essential to rule out functionally hypothyroid states induced by diet, stress, excess exercise and other environmental factors. Many clients often present with lowered temperature, with cold hands, feet and nose, altered bowel, sleep and emotional function, which can often be resolved with appropriate energy and decreased intestinal irritants.

Chronic pain increases cortisol production which decreases thyroid hormone production (Samuels & McDaniel, 1997) as does fasting or calorie restriction which induces a decrease in available T3 (thyroid hormone) (Hulbert, 2000).

This gives us two approaches 1) to reduce pain with appropriate therapy and to ensure that adequate energy modulates the suppression of excess cortisol and increases available thyroid for tissue organisation and recovery.

Hormones also affect tendons; diabetics and poor insulin profiles appear to create disorganised tendon structure but this may be a factor related to decreased available thyroid hormone. Hypothyroidism decreases available T3 within tendons, which can decrease growth, structure, and collagen production and create hypoxia of tissue leading to calcification.

Estrogen, although necessary for growth of tissue can often be found in excess creating problematic growth. Estrogen is also well known to decrease thyroid hormone and can provide an explanation why more females then men tend to be hypothyroid. The decrease in both thyroid hormone and progesterone can increase muccopolysacharides, which increase pressure in tissues, creating puffy, oedema like states. The swelling can be linked to many pain states which include carpal tunnel, which can be resolved with progesterone and thyroid in the absence of physical therapy. Progesterone also appears to induce myelination of nerves (surrounds and allows nerve conduction) and decreases inflammation (Milani et al 2010).

Energy production remains  a most potent form of therapy for decreasing pain, optimising rehabilitation and restoring tissue function.

References:

  1. Gao, N., Zhang, W., Zhang, Y., Yang, Q., & Chen, S. (2013). Carotid intima-media thickness in patients with subclinical hypothyroidism: A meta-analysis. Atherosclerosis, 227(1), 18–25. http://doi.org/10.1016/j.atherosclerosis.2012.10.070

  2. Hulbert, A. (2000). Thyroid hormones and their effects: a new perspective. Biological Reviews of the Cambridge Philosophical Society, 75(4), 519–631. http://doi.org/10.1017/S146479310000556X

  3. Milani, P., Mondelli, M., Ginanneschi, F., Mazzocchio, R., & Rossi, A. (2010). Progesterone - new therapy in mild carpal tunnel syndrome? Study design of a randomized clinical trial for local therapy. Journal of Brachial Plexus and Peripheral Nerve Injury, 5(1). http://doi.org/10.1186/1749-7221-5-11

  4. http://raypeat.com/articles/aging/aging-estrogen-progesterone.shtml

  5. Samuels, M. H., & McDaniel, P. A. (1997). Thyrotropin levels during hydrocortisone infusions that mimic fasting- induced cortisol elevations: A clinical research center study. Journal of Clinical Endocrinology and Metabolism, 82(11), 3700–3704. http://doi.org/10.1210/jcem.82.11.4376

Gestational diabetes and metformin-Is that the best that medical thinking has to offer?

Gestational diabetes or elevated blood sugar is often treated with metformin to improve blood sugar levels and considered the standard approach to treating gestational diabetes. The research suggests that it has little negative effects on the pregnant mother. However, does significant risks to both mother and baby if the incidence of premature birth count? Here are a few aspects to consider regarding the use of metformin to control blood sugar during pregnancy. A study of patients receiving a dose of metformin, combination of Clomiphene citrate (CC) and metformin both faired better than CC alone for the induction of ovulation (Neveu, Granger, St-Michel, & Lavoie, 2007).  As the combined group showed no benefit compared to metformin alone, one might consider that metformin alone may be considered for the positive effects.

In another study metformin and diet interventions showed a significant outcome compared to non-metformin-diet interventions. The metformin diet showed a reduction of 14 adverse events in a group of 76 expectant mothers, compared to the non-treated group of 36 adverse events out of 76 pregnancies (Glueck et al., 2013).

Thatcher and Jackson (Thatcher & Jackson, 2006) compared pregnancies of 188 women. 61 experienced miscarriages and 11 of those had stopped taking metformin, suggesting other abnormalities beyond metformin’s actions. 81% of women with pregnancies before metformin, 67% had prior miscarriages. 37% of these also miscarried again. Whilst metformin appeared to show minimal effects to mother and foetus 22% were born prematurely.

Whilst metformin has shown favourable outcomes in PCOS states, questions around pertinent biological mechanisms should warrant further discussion. It’s well known that two key endocrine actions may be compromised during the failure to achieve full gestation. Estrogen induces hypoxia in the uterus (Peat, 1997) and failure to produce adequate progesterone to counter the effects of estrogen may be implicated in the commonly fragile time around weeks 9-10 of pregnancy and incidence of miscarriage.

A concern of metformin are its affect transplacentally. Metformin appears to influence testicular size in males and affects sertoli cells. In females it may also lead to decreased androgen synthesis. Birth weight percentile is also significantly lower in pregnancies treated with metformin (Bertoldo, Faure, Dupont, & Froment, 2014)I Metformin has generally appeared safe in expecting mothers but considerable concern should be made regarding its long term effects to offspring and development most notably to reproductive tissues.

Hypothyroidism is a key factor in maintenance of pregnancy and alongside progesterone, thyroid hormone deficiency can be implicated in poor cellular energetics, production of adenosine triphosphate (ATP) and blood sugar regulation. There remains much debate about the issue of subclinical hypothyroidism, values and when to treat and perhaps metformin’s role despite showing some promises may be treating a symptom related to insulin sensitivity.

So perhaps these questions might be more pertinent before prescribing an agent that shows potentially negative effects to the fetus?

  1. What is the nutrition of the mother, is it enough and does it contain enough nutrients to enhance/maintain adequate progesterone/thyroid production?
  2. Is estrogen increasing at a rate that suppresses progesterone/thyroid levels and persistently decreases insulin sensitivity?
  3. Is there enough carbohydrate in the diet to ensure that carbohydrate is effectively utilised instead of persistent conversion of fats, increasing overall stress to both mother and fetus?
  4. Are the values of hypothyroidism and the identification of subclinical/functional hypothyroid factors appropriate?
  5. Is gestational diabetes a reflection of the above points?

The use of metformin, without questioning these mechanisms, remains at best a reduced treatment that fails to address a range of biological interactions and function.

References:

Bertoldo, M. J., Faure, M., Dupont, J., & Froment, P. (2014). Impact of metformin on reproductive tissues: an overview from gametogenesis to gestation. Annals of Translational Medicine2(6), 55. http://doi.org/10.3978/j.issn.2305-5839.2014.06.04

Glueck, C. J., Goldenberg, N., Pranikoff, J., Khan, Z., Padda, J., & Wang, P. (2013). Effects of metformin-diet intervention before and throughout pregnancy on obstetric and neonatal outcomes in patients with polycystic ovary syndrome. Current Medical Research and Opinion29(1), 55–62. http://doi.org/10.1185/03007995.2012.755121

Neveu, N., Granger, L., St-Michel, P., & Lavoie, H. B. (2007). Comparison of clomiphene citrate, metformin, or the combination of both for first-line ovulation induction and achievement of pregnancy in 154 women with polycystic ovary syndrome. Fertility and Sterility87(1), 113–120. http://doi.org/10.1016/j.fertnstert.2006.05.069

Peat, R. (1997). From PMS to Menopause: Female Hormones in context.

http://raypeat.com/articles/articles/glucose-sucrose-diabetes.shtml

Thatcher, S. S., & Jackson, E. M. (2006). Pregnancy outcome in infertile patients with polycystic ovary syndrome who were treated with metformin. Fertility and Sterility85(4), 1002–1009. http://doi.org/10.1016/j.fertnstert.2005.09.047

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?

 

References:

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