Cancer, depression, asthma, hair loss, vertigo, high blood pressure, eczema, infertility, hives, paranoia, hypoglycemia, hearing loss, and high cholesterol can all be caused by low thyroid levels. But the connection to the thyroid is often overlooked because Western medicine has separated each body system into a specialty, so a cardiologist is seen for heart problems, high blood pressure or high cholesterol; a dermatologist for eczema or hives; an oncologist for cancer; a gynecologist for infertility or reproductive system problems; and a psychiatrist for depression, paranoia and other mental health problems. Thyroid hormone affects every single cell in the body and can cause every problem just named. But our current system treats symptoms, and not the cause. If thyroid levels were optimized, one might not even need statins, blood pressure pills, steroid creams, birth control pills/fertility drugs, anti-depressants or anxiety meds.
Cancer patients are often physically cold.  Perhaps low body temperatures (a common hypothyroid symptom) allow cancer cells to thrive. In fact, hyperthermia, or high body temperature, is one form of cancer therapy.  The high temperature created would be analogous to a feverish temperature. Suboptimal thyroid function results in a sluggish liver, causing decreased methylation, the liver detox pathway that processes out hormones like estrogen. It is believed that estrogen dominance causes cancer (per Dr. John Lee), so low thyroid levels would be the actual cause of this.  One report stated the incidence of hypothyroidism is 50 to 80% in some cancer patient populations. 
Depression and mood disorders can also be caused by low thyroid levels. Low T3 levels in the brain correlate to low serotonin levels, which are associated with depression, thus the prescribing of SSRIs (selective serotonin reuptake inhibitors) to extend the life of the available serotonin. Low brain levels of T3 can be caused by insufficient T4 levels available for conversion, or low levels of the brain deiodinase enzymes that do the conversion, resulting in insufficient T3 for the brain’s needs. The addition of direct T3 in the form of liothyronine or natural desiccated thyroid has often lifted the depression. [12, 15]
Hair loss, eczema, hives, and dry skin often plague those with a thyroid condition. Hair loss is common in both hyperthyroid and hypothyroid states. Vitiligo, where patches of skin lose their pigment, is another autoimmune condition that can affect those with autoimmune thyroid disease.  A dermatologist can prescribe creams that may reduce symptoms, but better results may be obtained by correcting the underlying cause, low thyroid levels.
Vertigo, hearing impairment and tinnitus all correlate positively with the severity of hypothyroidism. In other words, the more hypothyroid one is, the worse the symptoms of vertigo, hearing impairment, and tinnitus.  Vertigo and hearing loss may be one of the first signs of myxedema and are usually reversible with treatment.  Cortisol keeps blood glucose stable, and severe hypoglycemia (low blood sugar) can result if cortisol levels are insufficient. Cortisol levels typically rise and fall in tandem with thyroid levels, so those who are hypothyroid also tend to have low cortisol. Some patients report improved hearing after a meal, which lends credence to the theory that blood glucose above a certain level is essential for hearing. Reactive hypoglycemia was present in 42% of patients with Meniere’s disease (who have vertigo), compared with only 15% in the control group. Meniere’s could then be a hypothyroid symptom, because low thyroid levels lead to low cortisol, which leads to low blood sugar, which leads to hypoglycemia, which correlates with Meniere’s.
High blood pressure (a high diastolic or lower number) and high cholesterol are common in cardiology patients. Cardiologist waiting rooms are often filled with slow-moving, overweight people who often have no energy to exercise. These are all hypothyroid symptoms. [1,2,3]
Infertility, irregular periods, or heavy periods are common in hypothyroid women. Thyroid hormone deficiency greatly affects the reproductive system. A surprising number of women on thyroid internet groups have had hysterectomies. Infertility and miscarriages are not uncommon. What is the connection between infertility and being hypothyroid? The body must have enough energy to ovulate, and that doesn’t often happen when hypothyroid. A hypothyroid woman is also physically cold, and one cannot “hatch” an egg unless the body is warm enough. [10,11] So even if ovulation and conception occur, the body may not be warm enough for the pregnancy to continue. Hypothyroid men have more abnormal sperm, while hyperthyroid men have sperm with reduced motility. The sperm return to normal once thyroid levels are normalized. 
Paranoid delusions, visual/auditory hallucinations, and bipolar behavior have been observed in some hypothyroid patients.  Paranoid individuals will string a series of events into a conspiracy against them, when in reality, there is no conspiracy. Auditory hallucinations have been reported in the thyroid internet forums: people say they continually hear whole symphonies and tunes in their heads, as if there were a radio in their head they couldn’t turn off. In a few of these cases, the people posted their labs and their Free T3 was considerably below mid-range. It would be an educated guess that these auditory hallucinations were caused by low thyroid levels.
The symptoms I’ve had that went completely away once my thyroid dose was raised: hypoglycemia, vertigo, asthma, and eczema. I would never have thought any of them were connected to my low thyroid levels. I was only aware of the common symptoms of hair loss, brain fog, and dry skin that I also had.
Getting your thyroid tested
If you’d like to have your thyroid levels tested, please ask for these thyroid tests, and note where your levels are in the thyroid lab ranges compared to healthy people. If you do not ask for these specific tests, your doctor will most likely just run a TSH test, which sadly, does not catch many cases of hypothyroidism. [TSH levels do not reflect thyroid levels]
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- Christian Meier, Jean-Jacques Staub, Carl-Bénédict Roth, Merih Guglielmetti, Maya Kunz, André R. Miserez, Jürgen Drewe, Peter Huber, Richard Herzog and Beat Müller. TSH-Controlled L-Thyroxine Therapy Reduces Cholesterol Levels and Clinical Symptoms in Subclinical Hypothyroidism: A Double Blind, Placebo-Controlled Trial (Basel Thyroid Study). The Journal of Clinical Endocrinology & Metabolism Vol. 86, No. 10 4860-4866, 2001. http://jcem.endojournals.org/cgi/content/abstract/jcem;86/10/4860
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- Alfredo Rebora and Franco Rongioletti. Clinical and Pathological Aspects of Skin Diseases in Endocrine, Metabolic, Nutritional and Deposition Disease. 2010, Part 1, Thyroid Disease, 27-33. http://www.springerlink.com/content/978-1-60761-180-6/#section=789615&page=1&locus=0
- David Jernigan. Cancer and Low Body Temperature [internet]. Hansa Center for Optimum Health; June 8, 2010, at 4:31 PM UTC [Accessed 1 January 2011] http://www.qondio.com/cancer-and-low-body-temperature
- J. van der Zee. Heating the patient: a promising approach? Annals of Oncology (2002) 13(8): 1173-1184.http://annonc.oxfordjournals.org/content/13/8/1173.abstract
- Friedolf Peters, C. Renate Pickhardt, Meinert Breckwoldt. Thyroid hormones in benign breast disease normalization of exaggerated prolactin responsiveness to thyrotropin-releasing hormone. Cancer 56:1082-1085, 1985. http://onlinelibrary.wiley.com/doi/10.1002/1097-0142%2819850901%2956:5%3C1082::AID-CNCR2820560520%3E3.0.CO;2-O/abstract
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- Udosen, E. O., Ugwu, O. A.. Edet, E. E. Thyroid Hormones Profile Indices for the Measurements of Infertility in Nigerian Women. Nigerian Journal of Physiological Sciences (ISSN: 0794-859X) Vol 17 Num 1-2, 2002. https://tspace.library.utoronto.ca/handle/1807/7933
- T. Maruo, K. Katayama, E.R. Barnea, M. Mochizuki. A Role for Thyroid Hormone in the Induction of Ovulation and Corpus luteum Function. Hormone Research, Vol. 37 (Suppl. 1):12-18, 1992. http://content.karger.com/ProdukteDB/produkte.asp?Doi=182338
- Carsten Kirkegaard and Jens Faber. The role of thyroid hormones in depression. European Journal of Endocrinology (1998) 138 1–9 http://www.eje-online.org/cgi/reprint/138/1/1.pdf
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- Cooper R, Lerer B. [The use of thyroid hormones in the treatment of depression]. [Article in Hebrew] Harefuah. 2010 Aug;149(8):529-34, 550, 549. http://www.ncbi.nlm.nih.gov/pubmed/21341434
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- David A. Moffat, John B. Booth, Andrew W. Morrison. Metabolic Investigations in Meniere’s Disease. The Journal of Laryngology & Otology. June 1979 93 : pp 545-561. http://journals.cambridge.org/action/displayAbstract;jsessionid=