Systematic review and meta-analysis on the effect of soy on thyroid function
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Abstract Soy foods have had an important dietary role in Asian countries for centuries, and in recent years they have become increasingly popular in Western countries as a result of their suggested health benefits. Nevertheless, there are some concerns that soy can have a negative effect on thyroid function and can alter the levels of thyroid hormones. The aim of this systematic review was to investigate the link between soy or soy product consumption and thyroid function via the measurement of thyroid hormone levels. A systematic review and meta-analysis was undertaken on all randomised controlled trials of studies including soy as an intervention and where free triiodothyronine (fT3), free thyroxine (fT4) and thyroid stimulating hormone (TSH) was measured. The search included PubMed, MEDLINE, EMBASE, Cochrane and sources for the grey literature. Quantitative data synthesis was performed using a random-effects model, with standardized mean difference (SMD) and 95% confidence interval as summary statistics. A total of 18 articles were suitable for review. The meta-analysis showed no significant changes in fT3 (WMD: 0.027 pmol/L, 95% CI: −0.052, 0.107, p = 0.499; I2: 55.58%), fT4 (WMD: −0.003 pmol/L, 95% CI: −0.018, 0.011, p = 0.656; I2: 87.58%) while an elevation in TSH levels was observed (WMD: 0.248 mIU/L, 95% CI: 0.001, 0.494, p = 0.049; I2: 80.31%) levels with soy supplementation. There was no evidence of publication bias. Soy supplementation has no effect on the thyroid hormones and only very modestly raises TSH levels, the clinical significance, if any, of the rise in TSH is unclear.
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A systematic review found no link between soy isoflavone intake and TSH nonresponse to levothyroxine, but observed a slight TSH increase with higher soy consumption.
“Regarding soy consumption, a systematic review found no relationship between isoflavone intake and TSH nonresponse to LT4 treatment, but did observe a slight increase in TSH levels in patients exposed to higher soy consumption.49”
From Refractory hypothyroidism: unraveling the complexities of diagnosis and management (2023) · cites this paper as [49]
A systematic review and meta-analysis of 18 studies found no overall effects of soy or isoflavones on thyroid function in adults, although a modest increase in TSH was noted in some studies of unclear clinical relevance.
“Recently, Otun et al. [149] conducted a systematic review and meta-analysis of 18 studies of the effects of soy foods/isoflavones on thyroid hormone function in adults. There were no overall effects of soy or isoflavones on thyroid function, although the authors did note a modest increase in TSH in some studies that was of unclear clinical relevance.”
From Plant Proteins: Assessing Their Nutritional Quality and Effects on Health and Physical Function (2020) · cites this paper as [149]
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- Authors
- Otun, J., Sahebkar, A., Östlundh, L., Atkin, S. L., & Sathyapalan, T.
- Affiliations
- University of Hull (GB)
- Mashhad University of Medical Sciences (IR)
- United Arab Emirates University (AE)
- Weill Cornell Medical College in Qatar (QA)
- Corresponding author
- Otun, Jemiliat
- Venue
- Scientific Reports
- Published
- 2019-03-08
- Volume
- 9
- Issue
- 1
- Pages
- 3964-3964
- ISSN
- 2045-2322 (ISSN-L)
- PMC
- PMC6408586
- OpenAlex
- W2921038322
- Cited by
- 68
- References
- 43
- Citations by year
- 2026: 8 · 2025: 9 · 2024: 11 · 2023: 11 · 2022: 9 · 2021: 12 · 2020: 7 · 2019: 1
- FWCI
- 1.11
- Type
- journal article
- Language
- en
- Open access
- gold
- doi.org
- Locations
- Scientific Reports (publishedVersion, cc-by)
- Europe PMC (PubMed Central) (publishedVersion, cc-by)
- PubMed Central (publishedVersion, cc-by)
- PubMed (publishedVersion)
- Repository@Hull (Worktribe) (University of Hull) (submittedVersion, cc-by)
- DOAJ (DOAJ: Directory of Open Access Journals) (submittedVersion)
- Topics
- Health Sciences › Medicine › Endocrinology, Diabetes and Metabolism › Thyroid Disorders and Treatments
- Health Sciences › Medicine › Pathology and Forensic Medicine › Phytoestrogen effects and research
- Health Sciences › Nursing › Nutrition and Dietetics › Selenium in Biological Systems
- Keywords
- soybean, soy products, thyroid function, thyroid hormones, free triiodothyronine, free thyroxine, thyroid-stimulating hormone, soy supplementation, thyroid hormone levels
- MeSH terms
- Animals, Biological Products, Humans, Glycine max, Thyroid Gland, Thyroid Hormones, Dietary Supplements
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