Evaluation of Levothyroxine Bioavailability after Oral Administration of a Fixed Combination of Soy Isoflavones in Post-menopausal Female Volunteers

Persiani, Stefano; Sala, Federica; Manzotti, C.; Čolović, Milena; Zangarini, Monique; Donazzolo, Yves; Barbetta, Beatrice; Vitalini, Cristina; Giacovelli, Giampaolo; Benvenuti, Claudio; Rovati, Lucio C.

doi:10.1055/s-0035-1555784

Cited by 10 publications

(9 citation statements)

References 13 publications

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“…Soy isoflavones-containing supplements are widely used by women to relieve menopausal symptoms. Persiani et al [ 58 ] conducted a randomized controlled trial on 12 post-menopausal women with hypothyroidism. They investigated the effect of soy isoflavones on bioavailability of l -T4 tablets.…”

Section: Resultsmentioning

confidence: 99%

Levothyroxine Interactions with Food and Dietary Supplements–A Systematic Review

2021

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Levothyroxine (l-thyroxine, l-T4) is a drug of choice for treating congenital and primary hypothyroidism. Although clinically significant interactions between l-T4 and food can alter the safety and efficacy of the treatment, they still seem to be generally underestimated by patients, physicians and pharmacists. This review aimed to investigate the effects of meals, beverages, and dietary supplements consumption on l-T4 pharmacokinetics and pharmacodynamics, to identify the most evident interactions, and to perform the recommendations for safe co-administering of l-T4 and food. A total of 121 studies were identified following a systematic literature search adhering to PRISMA guidelines. After full-text evaluation, 63 studies were included. The results proved that l-T4 ingestion in the morning and at bedtime are equally effective, and also that the co-administration of l-T4 with food depends on the drug formulation. We found limited evidence for l-T4 interactions with coffee, soy products, fiber, calcium or iron supplements, and enteral nutrition but interestingly they all resulted in decreased l-T4 absorption. The altered l-T4 efficacy when ingested with milk, juices, papaya, aluminium-containing preparations, and chromium supplements, as well as observed enhancement effect of vitamin C on l-T4 absorption, shall be further investigated in larger, well-designed studies. Novel formulations are likely to solve the problem of coffee, calcium and iron induced malabsorption of l-T4. Maintaining a proper time interval between l-T4 and food intake, especially for coffee and calcium, or iron supplements, provides another effective method of eliminating such interactions.

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Section: Resultsmentioning

confidence: 99%

Levothyroxine Interactions with Food and Dietary Supplements–A Systematic Review

2021

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“…In this latter case report, the efficacy of thyroxine treatment has been regained separating thyroxine from soy ingestion by 12 hours. A very recent pharmacokinetic study, performed in 12 patients on stable thyroxine treatment, demonstrated that bioavailability of thyroxine is superimposable in patients coingesting a fixed combination of soy isoflavones or with a six hours interval (196). A case report also described the impairment of pharmacological thyroxine homeostasis in a thyroidectomized patient after two weeks of large amount of papaya fruits consumption (113).…”

Section: Advance Article: Endocrine Reviewsmentioning

confidence: 99%

Gastrointestinal Malabsorption of Thyroxine

et al. 2018

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at the modification stage), and do not reflect editorial changes. No corrections/changes to the PDF manuscripts are accepted. Accordingly, there likely will be differences between the Advance Article manuscripts and the final, typeset articles. The manuscripts remain listed on the Advance Article page until the final, typeset articles are posted. At that point, the manuscripts are removed from the Advance Article page. DISCLAIMER: These manuscripts are provided "as is" without warranty of any kind, either express or particular purpose, or non-infringement. Changes will be made to these manuscripts before publication. Review and/or use or reliance on these materials is at the discretion and risk of the reader/user. In no event shall the Endocrine Society be liable for damages of any kind arising references to, products or publications do not imply endorsement of that product or publication.

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“…Apart from that, Persiani et al . have revealed that post-menopausal hypothyroid women who were given a dietary supplement containing 60 mg of isoflavone, a phytoestrogen in soy protein that has claimed to interfere with thyroid functions ( 25 ), has not affected L-thyroxine absorption ( 26 ) where the isoflavone content in isolated soy protein is up to 1 mg/g of protein ( 27 ). Considering these, it is unlikely that the presence of soy lecithin being a major contributor to the impaired thyroxine absorption.…”

Section: Discussionmentioning

confidence: 99%

Over-the-counter protein supplement resulting in impaired thyroxine absorption in a hypothyroid patient

Kumarathunga

Kalupahana

Antonypillai

2021

Endocrinology, Diabetes &Amp; Metabolism Case Reports

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Summary Whey protein is a popular dietary supplement that is claimed to provide multiple health benefits. It has been shown to delay gastric emptying and impair ileal nutrient absorption. Additionally, some of the other additives like papain enzyme, soy lecithin in these protein supplements could interfere with L-thyroxine absorption. There is no evidence in the literature for the effects of protein supplements on L-thyroxine absorption. Herein, we describe a case of a 34-year-old lady who was on endocrinology follow up for primary hypothyroidism with stable thyroid-stimulating hormone (TSH) levels within the normal range while on L-thyroxine with a dose of 125 µg daily for the last 3 years, presenting with mild hypothyroid symptoms and elevated TSH level following a recent introduction of a protein supplement by her physical care adviser. Her treatment adherence and ingestion technique were good throughout, she was not on other medications or herbal remedies, there were no other changes in her food pattern or features suggestive of malabsorption, she was not pregnant, was taking the same L-thyroxine brand and TSH test was done from the routine lab. Since the only factor which could have contributed to the deranged TSH levels was the recent introduction of the whey protein supplement, we advised her to stop the protein supplement while continuing the same dose of L-thyroxine. Her TSH level was repeated in 6 weeks and was found to be normal (1.7 mIU/L). Our case report demonstrates that over-the-counter protein supplements could interfere with L-thyroxine absorption. Therefore, patients on L-thyroxine should be cautious when taking them. Learning points Over-the-counter protein supplements could interfere with oral L-thyroxine absorption. The underlying mechanism could be the effect of whey protein by delaying gastric emptying and reduced responsiveness of organic anion transporters in the ileum, and there may be a contribution from other additives like papain and soy lecithin present in these supplements. When there is an elevation of previously stable thyroid-stimulating hormone (TSH) value in a hypothyroid patient on oral L-thyroxine, the patient's assessment should include inquiring for a recent introduction of protein supplement, in the absence of other well-known risk factors. Discontinuation of protein supplement results in normalization of thyroid function tests. Patients on oral L-thyroxine should be cautious when taking over-the-counter protein supplementation.

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Evaluation of Levothyroxine Bioavailability after Oral Administration of a Fixed Combination of Soy Isoflavones in Post-menopausal Female Volunteers

Abstract: The combination of soy isoflavones used in the present investigation does not affect the rate and extent of levothyroxine absorption when administered concomitantly in post-menopausal women.

Cited by 10 publications

References 13 publications

Levothyroxine Interactions with Food and Dietary Supplements–A Systematic Review

Levothyroxine Interactions with Food and Dietary Supplements–A Systematic Review

Gastrointestinal Malabsorption of Thyroxine

Over-the-counter protein supplement resulting in impaired thyroxine absorption in a hypothyroid patient

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