Hormonal balance is directly proportional to thyroid function and structure. The thyroid gland is a hormonal gland with the primary role of modulating growth, development, and metabolism by secreting thyroid hormones. These hormones are Triiodothyronine, also known as T3, Tetraiodothyronine, also called thyroxine or T4, and calcitonin. In addition to hormonal modulation, nutrition is an essential building block of thyroid hormones, and dietary patterns also interfere with their function. However, nutritional information on thyroid function is filled with bias and tends to complicate the detection between the facts and the fiction.
Soy isoflavones and thyroid function.
There exists a collective concern about the influence of soy ingestion and thyroid function. Nowadays, new dietary patterns are being adopted, and most households use soy as a protein alternative. Soy is a staple of Asian cuisine. However, it has gained attention in Westernized countries due to its health benefits.
Soy’s health benefits:
- Protection against osteoporosis.
- Reduces risk of cardiovascular disease and diabetes.
- Lowers risk of breast and prostate cancer.
Furthermore, the same isoflavones and soy protein associated with the benefits mentioned above are the same ones associated with hormonal disbalance.
Isoflavones: These components are a subclass of plant-derived flavonoids. The main isoflavones contained in soy in an inactive form are genistin and daidzin. Furthermore, these inactive compounds become hydrolyzed and deconjugated in the gut by B glycosidases produced by the intestinal bacteria. This last mechanism leads the conversion to the biologically active forms of isoflavones such as genistein and daidzein.
Soy: fiction or fact.
Regardless of the common speculation of isoflavones being detrimental to thyroid function, meta-analyses show that soy supplementation has no harmful effect on thyroid function.
But how? Otun and colleagues performed a systematic review that included 18 articles that measured thyroid hormone levels and soy supplementation. This review reports that only TSH levels had a significant change with soy protein and soy isoflavone supplementation. However, T3 and T4 levels were not affected by soy ingestion. Furthermore, this suggests that while soy can affect thyroid function, it cannot develop a clinical condition. In addition, these same results were reproduced in studies including patients with subclinical hypothyroidism and T2DM.
L-carnitine and thyroid hormone levels
The quaternary ammonium compound carnitine works as a cofactor for the B- oxidation of fatty acids. Indeed, carnitine facilitates the transports of long-chain fatty acids across the mitochondrial membrane, promoting ATP production.
Additionally, carnitine supplementation improves cardiac function by reducing oxidative stress, inflammation, and necrosis of cardiac myocytes.
Carnitine: fiction or fact.
In addition to the importance of carnitine supplementation in athletes, the effects of carnitine have been studied in thyroid function. A small study that observed L-carnitine supplementation in patients with Graves’ disease improved basal metabolic rate, reduced fibrillation, and improved overall wellbeing.
Another study pointed out that after supplementing L-carnitine in hyperthyroid patients, they became euthyroid without any change in the thyroid function tests. This same result was confirmed years after when a controlled clinical study addressed L-carnitine’s function in antagonizing elevated levels of thyroid hormones.
Inositol was previously known to be a vitamin B8. Accordingly, it is strongly associated with this group of vitamins due to its metabolic role in the body. In addition, this component forms a critical part of the cellular membrane since it is found in phospholipids. Foods like fruits, beans, grains, and nuts are rich in Myo-inositol, which is the most abundant form of this nutrient.
Inositol: fiction or fact
Inositol plays a crucial part in cellular and hormone signalings, such as gonadotropins, TSH, and insulin.
In the thyroid, imbalances in the inositol metabolism can impair thyroidal hormone biosynthesis, storage, and secretion. In the particular case of TSH signaling, inositol acts like a signaling potentiator, while another signaling cascade is cAMP-dependent. Studies have found that Myo-inositol supplementation in 48 women with subclinical autoimmune hyperthyroidism reduced TSH levels for a longer time when compared to selenomethionine supplementation.
Nowadays most patients are taking at least one supplement or multivitamin. For a clinician, the key is to ask the patient what are they taking and the reason for taking this supplement. Another important issue is to have current information about nutritional supplements with the proper amount of nutrients. – Ana Paola R. Arciniega, MS.
Otun, Jemiliat et al. “Systematic Review and Meta-analysis on the Effect of Soy on Thyroid Function.” Scientific Reports vol. 9,1 3964. 8 Mar. 2019, doi:10.1038/s41598-019-40647-x
Benvenga, Salvatore, et al. “Nutraceutical Supplements in the Thyroid Setting: Health Benefits beyond Basic Nutrition.” Nutrients 11.9 (2019): 2214.
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Dr. Alex Jimenez DC, MSACP, CCST, IFMCP*, CIFM*, CTG*
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