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In conversations regarding the increasing number of people that are obese (in an American or European context), often times claims regarding thyroid function being a significant contributor to these developments come up. I've tried finding sources written by medical experts addressing a lay audience to clarify these issues, but I can't find anything that makes the issue clear enough for me.

Question(s):

  • Is there a known causal relationship that goes "abnormal thyroid function -> higher weight"? I don't know whether thyroid issues develop later in life or are congenital, or how much of an impact they have, so this question might be ill-phrased.

  • If abnormal thyroid function is known to have effects on weight gain, can we quantify how many people are affected by this, and how much weight gain per person is caused by this?

  • Are there thyroid conditions that make it extremely difficult not to put on weight (say, you continue to put on weight despite eating less than 1000 calories a day), and if so, do we know how many people are affected by those conditions?

  • If this is too many questions in one post, I'm happy to break it up into multiple questions. – G. Bach May 17 '18 at 21:00
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    jamanetwork.com/journals/jamainternalmedicine/fullarticle/… - Most notably this: In our community-based sample of participants with thyroid function within the reference range, we observed that the baseline serum TSH concentration was strongly and linearly associated with cross-sectional weight in women and men. – JohnP May 17 '18 at 21:34
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The relationship between thyroid function and body weight is bidirectional and complex.

It is known for decades, if not centuries, that cretinism (only in the end of the 19th century to be associated to hypothyroidism) may be accompanied by weight gain and that thyrotoxicosis may result in weight loss. As early as in 1835 Robert J. Graves described that ladies affected by goitre and palpitations (probably due to hyperthyroidism resulting from the disease which is now named after him) were remarkably thin [2]. Five years later the German physician Karl von Basedow described the same condition, where a lady suffering from goitre, Exophthalmos and palpitations had severely emaciated [3]. In 1883 the swiss surgeon Theodor Kocher described weight gain after total thyroidectomy [4]. Ten years later, in 1893 William Ord described rapid weight loss, after myxoedematous patients were set on treatment with thyroid extreact [5].

Today it is known that over one third of hypothyroid infants have a birth weight greater than the ninetieth percentile [6, 7]. However, an “atypical” form of hypothyroidism may be associated to low birth weight [8]. Of course, weight gain in hypothyroidism isn’t restricted to infants, but common in adults, too. Hypothyroidism is assumed to contribute 2.5 to 5 kg (5 to 10 pounds) to body weight [9].

On the other hand, changes in body weight may also result in changes of thyroid function. A number of studies, as recently extensively reviewed [10, 11], described elevated TSH levels and increased total step-up deiodinase activity in patients with weight gain. These changes were reversible after weight loss [12]. On the other hand, low T3 syndrome is a well-known consequence of anorexia and starvation [13, 14].

Probably, these changes represent adaptive responses of pituitary-thyroid axis to type 1 or type 2 allostasis, respectively [15]. The observed mechanisms may contribute to some kind of autoregulation of weight in conditions of changing supply with energy.

Autoregulation of weight in obesity [Chatzitomaris et al. 2017, CC BY license]

To use thyroid hormones as an adjunct treatment in obesity is strongly discouraged, since cardiovascular side effects may be significant [16].

References

1: https://www.frontiersin.org/articles/10.3389/fendo.2017.00163/full

2: Graves RT. Lecture XII. in: Clinical Lectures. 1835 25-43.

3: von Basedow K. Exophthalmos durch Hypertrophie des Zellgewebes in der Augenhöhle. Wochenschrift für die gesammte Heilkunde. 1840 13:197-228.

4: Kocher T. Ueber Kropfexstirpation und ihre Folgen. Archiv für klinische Chirurgie. 1883 29:254-335.

5: Ord WM, White E. Clinical Remarks on Certain Changes observed in the Urine in Myxoedema after the Administration of Glycerine Extract of Thyroid Gland. Br Med J. 1893 Jul 29;2(1700):217. PMID: 20754379; PMCID: PMC2422016. https://www.ncbi.nlm.nih.gov/pubmed/20754379 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2422016/

6: LaFranchi SH. Hypothyroidism. Pediatr Clin North Am. 1979 Feb;26(1):33-51. PMID: 460987. https://www.ncbi.nlm.nih.gov/pubmed/460987

7: Rastogi MV, LaFranchi SH. Congenital hypothyroidism. Orphanet J Rare Dis. 2010 Jun 10;5:17. doi: 10.1186/1750-1172-5-17. PMID: 20537182; PMCID: PMC2903524. https://www.ncbi.nlm.nih.gov/pubmed/20537182/ http://dx.doi.org/10.1186/1750-1172-5-17

8: Mandel SJ, Hermos RJ, Larson CA, Prigozhin AB, Rojas DA, Mitchell ML. Atypical hypothyroidism and the very low birthweight infant. Thyroid. 2000 Aug;10(8):693-5. PMID: 11014314. https://www.ncbi.nlm.nih.gov/pubmed/11014314

9: American Thyroid Association: Thyroid & Weight. 2016. https://www.thyroid.org/wp-content/uploads/patients/brochures/Thyroid_and_Weight.pdf

10: Pacifico L, Anania C, Ferraro F, Andreoli GM, Chiesa C. Thyroid function in childhood obesity and metabolic comorbidity. Clin Chim Acta. 2012 Feb 18;413(3-4):396-405. doi: 10.1016/j.cca.2011.11.013. PMID: 22130312. https://www.ncbi.nlm.nih.gov/pubmed/22130312 http://dx.doi.org/10.1016/j.cca.2011.11.013

11: Fontenelle LC, Feitosa MM, Severo JS, Freitas TE, Morais JB, Torres-Leal FL, Henriques GS, do Nascimento Marreiro D. Thyroid Function in Human Obesity: Underlying Mechanisms. Horm Metab Res. 2016 Dec;48(12):787-794. PMID: 27923249. https://www.ncbi.nlm.nih.gov/pubmed/27923249

12: Reinehr T. Obesity and thyroid function. Mol Cell Endocrinol. 2010 Mar 25;316(2):165-71. doi: 10.1016/j.mce.2009.06.005. PMID: 19540303. https://www.ncbi.nlm.nih.gov/pubmed/19540303 http://dx.doi.org/10.1016/j.mce.2009.06.005

13: Rothenbuchner G, Loos U, Kiessling WR, Birk J, Pfeiffer EF. The influence of total starvation on the pituitary-thyroid-axis in obese individuals. Acta Endocrinol Suppl (Copenh). 1973;173:144. PMID: 4542076. https://www.ncbi.nlm.nih.gov/pubmed/4542076

14: Portnay GI, O'Brian JT, Bush J, Vagenakis AG, Azizi F, Arky RA, Ingbar SH, Braverman LE. The effect of starvation on the concentration and binding of thyroxine and triiodothyronine in serum and on the response to TRH. J Clin Endocrinol Metab. 1974 Jul;39(1):191-4. PMID: 4835133. https://www.ncbi.nlm.nih.gov/pubmed/4835133

15: Chatzitomaris A, Hoermann R, Midgley JE, Hering S, Urban A, Dietrich B, Abood A, Klein HH, Dietrich JW. Thyroid Allostasis-Adaptive Responses of Thyrotropic Feedback Control to Conditions of Strain, Stress, and Developmental Programming. Front Endocrinol (Lausanne). 2017 Jul 20;8:163. doi: 10.3389/fendo.2017.00163. PMID: 28775711; PMCID: PMC5517413. https://www.ncbi.nlm.nih.gov/pubmed/28775711 http://dx.doi.org/10.3389/fendo.2017.00163

16: Krotkiewski M. Thyroid hormones in the pathogenesis and treatment of obesity. Eur J Pharmacol. 2002 Apr 12;440(2-3):85-98. PMID: 12007527. https://www.ncbi.nlm.nih.gov/pubmed/12007527

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    That is a long list of references, thanks! Since I have no medical eduaction, let me summarize: the hormones the thyroid produces regulate metabolism, and hypothyroidism leads to a lower basal metabolic rate, which leads to a small weight gain (up to 2.5 - 5kg). Other conditions that come with abnormal thyroid function can actually lead to a metabolism that favors weight loss instead of weight gain. Body weight also changes thyroid behavior and can cause abnormal hormone levels being produced instead of being caused by thyroid conditions, it's not a one-way interaction. Sound about right? – G. Bach May 20 '18 at 1:50
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    The relationship is complex, especially at the hypothalamic level. Somewhat Simplifying we can say that thyroid hormones increase energy expenditure, that starvation down-regulates thyroid hormone metabolism (type 1 allostasis) and that a surplus in energy (metabolic syndrome as a consequence of type 2 allostasis) up-regulates formation of T3. These mechanisms are partly compensatory in nature. Reference: Martínez-Sánchez N et al. Hypothalamic AMPK-ER Stress-JNK1 Axis Mediates the Central Actions of Thyroid Hormones on Energy Balance. Cell Metab. 2017 t1p.de/d5i9 – jwdietrich May 20 '18 at 8:48

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