Fish and the Thyroid: A Janus Bifrons Relationship Caused by Pollutants and the Omega-3 Polyunsaturated Fatty Acids

Abstract

Benefits of the omega-3 polyunsaturated fatty acids (PUFA) on a number of clinical disorders, including autoimmune diseases, are widely reported in the literature. One major dietary source of PUFA are fish, particularly the small oily fish, like anchovy, sardine, mackerel and others. Unfortunately, fish (particularly the large, top-predator fish like swordfish) are also a source of pollutants, including the heavy metals. One relevant heavy metal is mercury, a known environmental trigger of autoimmunity that is measurable inside the thyroid. There are a number of interactions between the omega-3 PUFA and thyroid hormones, even at the level of the thyroid hormone transport proteins. Concerning the mechanisms behind the protection from/amelioration of autoimmune diseases, including thyroiditis, that are caused by the omega-3 PUFA, one can be the decreased production of chemokines, a decrease that was reported in the literature for other nutraceuticals. Recent studies point also to the involvement of resolvins. The intracellular increase in resolvins is associated with the tissue protection from inflammation that was observed in experimental animals after coadministration of omega-3 PUFA and thyroid hormone. After having presented data on fish consumption at the beginning, we conclude our review by presenting data on the market of the dietary supplements/nutraceuticals. The global omega-3 products market was valued at USD 2.10 billion in 2020, and was projected to go up at a compound annual growth rate of 7.8% from 2020 to 2028. Among supplements, fish oils, which are derived mainly from anchovies, are considered the best and generally safest source of omega-3. Taking into account (i) the anti-autoimmunity and anti-cancer properties of the omega-3 PUFA, (ii) the increasing incidence of both autoimmune thyroiditis and thyroid cancer worldwide, (iii) the predisposing role for thyroid cancer exerted by autoimmune thyroiditis, and (iv) the risk for developing metabolic and cardiovascular disorders conferred by both elevated/trendwise elevated serum TSH levels and thyroid autoimmunity, then there is enough rationale for the omega-3 PUFA as measures to contrast the appearance and/or duration of Hashimoto’s thyroiditis as well as to correct the slightly elevated serum TSH levels of subclinical hypothyroidism.

The prevalence of thyroid nodules and its factors among Chinese adult women: A cross-sectional study

“…Therefore, future studies should specifically analyze the impact of dietary diversity on health according to individual health cognition and economic status, and pay attention to food attributes and diet balance. Some studies have also found an increase in thyroid disease in people exposed to polluted environmental and food, such as petrochemical workers, areas contaminated with organochlorine pesticides or polychlorinated biphenyls, or near aluminum foundries ( 45 , 53 ). Fish (particularly the large, top-predator fish like swordfish) from polluted waters have more likely high levels of mercury.…”

“…Mercury was found to be a known autoimmune environmental trigger and can be measured inside the thyroid ( 54 ). Fortunately, nutrients such as omega-3 fatty acids and selenium found in fish have been shown to exert a protective effect against thyroid disease and reduced the risk of cancer ( 53 ). Therefore, future research should not ignore the possibility of food contamination.…”

Association of Hypothyroidism and the Risk of Cognitive Dysfunction: A Meta-Analysis

“…Although the mechanism of the association between hypothyroidism and cognitive dysfunction is not precise, it is still essential to focus on the prevention of hypothyroidism. Modifying iodine deficiency [64] or iodine excess [65], nutraceuticals such as omega-3 PUFA supplementation [66], and improving sleep quality [67] all have positive implications. Accurate assessment of whether hypothyroidism is associated with an increased risk of dementia or cognitive impairment is important for the accurate prevention and treatment of dementia.…”

Commentary: Fish and the thyroid: A Janus Bifrons relationship caused by pollutants and the omega-3 polyunsaturated fatty acids

“…We read with interest the paper published in the journal by Benvenga S, et al (1) about the complex interplay between thyroid disorders and the intake of omega-3 polyunsaturated fatty acids (PUFAs), whose main dietary source is represented by fish. In their review, Benvenga et al (1) put a specific warning on the potential heavy metal content in fish and the risks deriving from its consumption, suggesting that there would be the place for the use of nutraceuticals containing omega-3 PUFAs to prevent or contrast autoimmune thyroiditis, overcoming the risk of contaminants in fish. Although pharmacological supplementation would be sometimes useful, also limiting dietary consumption to fishes containing low levels of pollutants and including fish within the framework of a healthy diet represent a good choice.…”

“…We read with interest the paper published in the journal by Benvenga S, et al. ( 1 ) about the complex interplay between thyroid disorders and the intake of omega-3 polyunsaturated fatty acids (PUFAs), whose main dietary source is represented by fish. In their review, Benvenga et al.…”