Hypothyroidism
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Revision as of 21:03, 30 November 2012
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Hypothyroidism is a condition in which the thyroid gland doesn't produce adequate levels of thyroid hormones, resulting in symptoms such as lethargy and weight gain. It affects perhaps 5% of the adult American population, most of whom are women with subclinical symptoms.
Of course, with so much of the American population overweight and with lethargy having so many possible causes, it was inevitable that some woo meisters would claim that hypothyroidism is an "epidemic" and that you probably have it. Or, if you've been diagnosed with hypothyroidism and you still feel tired and fat on the medication, that your hypothyroidism must not be adequately treated yet.
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History of treatment
If hypothyroidism is cause by iodine deficiency, the treatment is simply to increase iodine intake. However, iodine deficiency is very rare in the industrial world. Thus, most cases of hypothyroidism in the modern world are caused by some other dysfunction of the body's thyrotropic feedback control.
In 1909, the first treatment for non-iodine-deficient hypothyroidism became available. This treatment was called Desiccated Thyroid, and as its name implied it consisted of the ground-up thyroid glands of cows and/or pigs. Since the Armour meat packing company (the makers of Spam) had cow-and-pig parts to spare, they became the first providers of desiccated thyroid; desiccated thyroid is still to this day sold under the Armour brand name, although the name is currently owned by Forest Laboratories.
Over the course of the 20th century, individual thyroid-related hormones began to be identified:
- Thyrotropin-releasing hormone (TRH), which is secreted by the hypothalamus.
- Thyroid-stimulating hormone (TSH), a.k.a. thyrotropin, which is secreted by the pituitary in response to TRH.
- Thyroxine (T4), which is secreted by the thyroid in response to TSH; this tells the hypothalamus to produce less TRH, and can also tell the pituitary to produce less TSH.
- Triiodothyronine (T3), which is secreted in small quantities by the thyroid and is also created by deiodination of T4; this is the main, active thyroid hormone that stimulates bodily activity. Like T4, it can also reduce the secretion of TRH and TSH from the hypothalamus and pituitary.
- Reverse triiodothyronine (rT3), which is also created by deiodination of T4; this hormone is basically inactive.
... along with at least one important enzyme:
- Thyroid peroxidase (TPO), which makes iodine available for incorporation into T4 and T3.
Over the years, diagnostic tools have steadily improved, drug purity requirements have tightened across the board, and understanding of the roles of the various thyroid hormones has deepened. As a result, concern arose over desiccated thyroid for two reasons: (1) The concentration of the important thyroid hormones in any one sample can vary widely, since no two cows and pigs have identical thyroid glands; and (2) the ratio of T4 to T3 in cow and pig thyroid glands is considerably higher than the ratio of T4 to T3 in a healthy adult human.
In response to these concerns, the pharmaceutical industry developed synthetic T4, called levothyroxine (marketed under the brand name Synthroid). It was a little more expensive to produce than desiccated thyroid, but it allowed for the dosage to be much more precisely controlled. Synthetic T3, called liothyronine and marketed under the brand name Cytomel, followed soon thereafter. (Desiccated thyroid manufacturers have tried to keep up with the times; the current USP standards for thyroid extract, for example, are much stricter than the standards from the middle of the 20th century.)
Since in the vast majority of hypothyroid cases, the only dysfunction is in the production of T4, most endocrinologists switched their prescription regimen to levothyroxine-only. This was, and still is, effective for the vast majority of hypothyroid patients.
Inadequate T3?
In a minority of cases, however, T4-only supplementation seemed to prove inadequate. In addition to reduced production of T4 by the thyroid gland, some patients' bodies also appeared to exhibit a reduced ability to turn T4 into T3 -- or turned too much T4 into the (inactive) reverse T3 instead.
Thus, a few patients who had been doing fine on desiccated thyroid (which has both T4 and T3) found themselves not doing so well on straight T4 pills. Some endocrinologists responded to this by adding synthetic T3 to those patients' dosing regimen, but other endocrinologists -- perhaps inspired by the good results the vast majority of their other hypothyroid patients were experiencing on T4 alone -- simply assumed that the dissatisfied patient's new symptoms weren't due to hypothyroidism and refused to give out T3 prescriptions.
Evidence for the benefit of T3 supplementation is mixed. There are studies showing that stress, or at least TNF which can be released by stress, decreases the conversion of T4 to T3,[1], but no conclusive benefit has been shown for adding T3 to an existing T4 regimen in general.[2][3] As of 2002, the American Association of Clinical Endocrinologists recommends only the prescription of T4 for hypothyroid patients.[4]
Diagnostic tests
Today, the most widely prescribed test for hypothyroidism is a test for the level of TSH in the blood. The higher the TSH level, the more the hypothalamus/pituitary "feel" that there isn't enough T4/T3 in the blood stream. The "normal" upper limit for TSH (i.e. the blood concentration above which an untreated patient should be diagnosed with hypothyroidism) is between 3.0 and 6.0 μIU/mL, depending on whom you talk to. The current therapeutic target range for TSH in hypothyroid patents is between 0.3 to 3.0 μIU/mL; a TSH level above this range indicates the patient is probably undermedicated.
The most common cause of hypothyroidism in the Western world is an autoimmune disorder called Hashimoto's thyroiditis, in which the body manufactures antibodies that attack its own TPO enzymes. As such, tests exist for the anti-TPO antibodies that are present in the blood in this disease.
Tests also exist for Free T3, Total T3 (most T3 is bound up in blood glycoproteins), and Reverse T3. Legitimate argument exists over the validity of these tests. T3 has a rather short half-life in vivo, and serum T3 levels can vary over the course of a day depending on a number of factors. The ratio of Free T3 to Reverse T3 has also been touted as a useful diagnostic tool for those patients with TSH levels below the hypothyroid range, but Reverse T3 has a longer half-life than T3 does, and so the ratio could theoretically vary over the course of a day as T3 is broken down but Reverse T3 isn't.
Some practitioners claim that the pituitary preferentially senses T4 over T3, and thus will automatically reduce its TSH output in response to T4 levels even if inadequate T3 is still being produced. Others have gone so far as to claim that Reverse T3 can "clog up" the cellular T3 receptors, producing "tissue resistance" to T3[5] which results in reduced response even when your T3 levels should be adequate. What the evidence is for either of these claims is likely a matter of debate.
Listen, Damn You!
Suppose a hypothyroid patient is taking a prescription for synthetic T4, and her TSH levels are now down within the therapeutic target range. But, she still feels lethargic, fat, and unhappy. It could be because her T3 levels are inadequate, but it might also be because of factors that have nothing to do with her hypothyroidism. A good endocrinologist might be willing to test for T3 levels, or adjust the dose of T4 to target the low end of the normal TSH range instead of the high end, or even try supplementing the T4 with a small amount of T3 — but (s)he should also be wary of overmedicating her patient all the way into the hyperthyroid range.
As a result, books like Stop the Thyroid Madness scream up-and-down about the need to get your doctor to LISTEN!! to you. By which they mean, if your doctor isn't giving you exactly the drugs you tell them to, then they are an evil dupe in the hip pocket of Abbot Laboratories and you should keep looking for one until you find one that will rubber-stamp your prescription mandates.
Online rants, posted by folks who may or may not be readers of the above book, are similar. "Doctors need to LISTEN!" they scream. "YOU'RE NOT LISTENING!!! LISTEN TO ME RIGHT NOW YOU MOTHERF#$%ING %^&$$%#S OR I'M GOING TO KILL YOU WHERE YOU MOTHERF$%@ING STAND YOU USELESS PILE OF GARBAGE!!!!!!!"
False dichotomy
Since desiccated thyroid is derived from ground up animal glands, it is therefore "natural", and must therefore inherently be better than that wicked, man-made synthetic T4.
The book Stop the Thyroid Madness, by Janie A. Bowthorpe, seems to imply that the only two courses of treatment available to a hypothyroid patient are an evil corporate-sponsored dose of synthetic T4 and nothing else, or the "natural alternative" of desiccated thyroid (which she almost always calls "Armour thyroid"). Almost no mention is made anywhere in the book of the existence of synthetic T3. Nowhere is the suggestion made of asking ones doctor to add synthetic T3 into the prescription mix, if you're not feeling fully treated on T4 alone. The few places that do mention people who have been prescribed synthetic T3 are quick to remind the reader: "But Armour Thyroid contains everything, so you should use that instead!"
For all of her claims that "mainstream" endocrinologists are receiving kickbacks from Abbot Laboratories, it is not known whether Ms. Bowthorpe is receiving kickbacks from Forest Labs.
Bowthorpe's book isn't the only hypothyroidism information source to present this false dichotomy. This about.com article, for example, also touts the virtues of desiccated thyroid extract over a regimen of pure synthetic T4, while neglecting to mention the synthetic T3 option except in an off-the-cuff remark about inflexible endocrinologists.
Synthetic T4 shelf life
According to an FDA press release from 2007[6], synthetic T4 can break down if stored in a hot or humid environment (like, say, a bathroom with a working tub or shower).
To desiccated thyroid proponents, this was one more reason not to trust synthetic T4. To more sane individuals, though, it brings up the question of whether the natural T4 in desiccated thyroid doesn't also break down if stored in a hot or humid environment.
Hypothyroid diet
Not content with a choice between modern synthetic treatments that have been proven to work, and the older ground-up-thyroid gland that was also proven to work in its own time, various woo peddlers have chimed in with the claim that you can cure your hypothyroidism by diet.
There are some foods known to be goitrogenic[wp], such as soybeans and cauliflower; these foods contain isoflavones that can interfere with thyroid peroxidase, thereby reducing the thyroid gland's ability to manufacture T4 -- but only in cases of iodine deficiency.[7] However, the diet woo meisters go far beyond simply recommending that you reduce your intake of goitrogenic foodstuffs or ensure adequate iodine levels.
The Mayo Clinic says there's no evidence for dietary control of hypothyroidism, outside of ensuring that the patient doesn't eat certain foodstuffs too soon after taking hormone supplements.[8] Evidence-based medicine has never stopped diet woo before, though.[9][10][11][12]
Hypothyroidism treatments as weight loss gimmicks
One of the possible symptoms of hypothyroidism is weight gain. One of the possible symptoms of hyperthyroidism is weight loss. It didn't take long for those desperate to find an easy weight loss gimmick to think of deliberately taking thyroid hormones even when thyroid function is normal.
The American Thyroid Association has this to say about the subject:
“”Thyroid hormones have been used as a weight loss tool in the past. Many studies have shown that excess thyroid hormone treatment can help produce more weight loss than can be achieved by dieting alone. However, once the excess thyroid hormone is stopped, the excess weight loss is usually regained. Furthermore, there may be significant negative consequences from the use of thyroid hormone to help with weight loss, such as the loss of muscle protein in addition to any loss of body fat. Pushing the thyroid hormone dose to cause thyroid hormone levels to be elevated is unlikely to significantly change weight and may result in other metabolic problems.
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| —Thyroid and Weight (PDF), American Thyroid Association |
Dietary supplements used to be sold which contained actual thyroid hormones. Today, however, legal access to these drugs is impossible without a prescription. That hasn't stopped certain unscrupulous manufacturers from giving "thyroidally suggestive" names to their dietary supplements, like "T-3"[13], even though they contain no triiodothyronine.
Footnotes
- ↑ Ongphiphadhanakul, B; Fang, SL; Tang, KT; Patwardhan, NA; Braverman, LE (1994). "Tumor necrosis factor-alpha decreases thyrotropin-induced 5'-deiodinase activity in FRTL-5 thyroid cells". European journal of endocrinology 130 (5): 502–7. PMID 8180680.
- ↑ Escobar-Morreale, H. F.; Botella-Carretero, JI; Escobar Del Rey, F; Morreale De Escobar, G (2005). "Treatment of Hypothyroidism with Combinations of Levothyroxine plus Liothyronine". Journal of Clinical Endocrinology & Metabolism 90 (8): 4946–54. PMID 15928247.
- ↑ Joffe, R. T.; Brimacombe, M.; Levitt, A. J.; Stagnaro-Green, A. (2007). "Treatment of Clinical Hypothyroidism With Thyroxine and Triiodothyronine: A Literature Review and Metaanalysis". Psychosomatics 48 (5): 379–84. PMID 17878495.
- ↑ American Association of Clinical Endocrinologists (November/December 2002). "Medical Guidelines For Clinical Practice For The Evaluation And Treatment Of Hyperthyroidism And Hypothyroidism" (PDF). Endocrine Practice 8 (6): 457–69. PMID 15260011. https://www.aace.com/files/hypo-hyper.pdf.
- ↑ http://www.thyroid-rt3.com/whatdo.htm
- ↑ Thyroid Drug Potency is Being Tightened: FDA Changes Specs for Levothyroxine
- ↑ Doerge DR, Sheehan DM (June 2002). "Goitrogenic and estrogenic activity of soy isoflavones". Environ. Health Perspect. 110 Suppl 3: 349–53. PMC 1241182. PMID 12060828. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1241182.
- ↑ Is there any truth to the hypothyroidism diet? Can certain foods increase thyroid function?
- ↑ Smart Foods For Hypothyroidism
- ↑ LiveStrong hypothyroidism diet
- ↑ The HypoThyroid Diet: Lose Weight and Beat Fatigue in 21 Days
- ↑ The Thyroid Diet: Manage Your Metabolism for Lasting Weight Loss; some sound advice mixed in with herbal supplement woo
- ↑ S.A.N. T-3