Every cell in the body communicates with the thyroid gland; it orchestrates the pace at which metabolism works. Its importance is recognized, and many researchers hone in on the influence of micronutrients in this gland's health, with iodine and selenium (Se) at the forefront.
This month we will discuss two research papers published in 2015:
- Wu Q, Rayman MP, Lv H et al. Low population selenium status is associated with increased prevalence of thyroid disease. J Clin Endocrinol Metab 2015;100:4037-47.
- Winther KH, Bonnema SJ, Cold F et al. Does selenium supplementation affect thyroid function? Results from a randomized, controlled, double-blinded trial in a Danish population. Eur J Endocrinol 2015;172:657-67.
1. The study published in 2015 by Wu et al. investigated for the first time two areas in China's Shaanxi province --similar genetics, culture, lifestyle, iodine levels--with significantly different Se concentration in their soil and crops. The team set out to determine the prevalence of thyroid disease in 6,152 participants, based on their Se status. For the purposes of the study, Ziyang county was designated as "adequate-Se" and Ningshan county was named "low-Se."
Participants completed: an interview; a questionnaire that included demographic data, history of disease, and habits (e.g. food consumption and smoking); clinical examination; and a thyroid ultrasound. A fasting blood sample was also collected to measure serum levels of: thyroid antibodies (TPO-Ab), thyroid hormones (TSH, T4, T3), and Se. Ultrasound and blood tests results were used to define individuals as having thyroid disease.
Se level was significantly higher in the adequate-Se county than in the low-Se county (103.6 vs 57.4 mcg/L), accounting for additional aspects that could influence the results: consumption of meat, eggs, and green tea; education level; and occupation (i.e. farming).
As the authors hypothesized, thyroid disease was more prevalent in the Ningshan county --associated with low Se-- (951 participants, 30.5%) than in the Ziyang county --associated with adequate Se-- (518 participants, 18.0%). The risk of having any thyroid disease was 69% higher in the low Se population, with prevalence of conditions related to an underactive gland (subclinical hypothyroidism, enlarged thyroid, overt hypothyroidism, autoimmune thyroiditis).
This large study is significant because it aligns with previous results found in low Se areas and because Se levels found in the participants are comparable to the status in other parts of the world.
Se protects the cells through several mechanisms, and populations currently living with low Se status would benefit from an intake increase; Se-enriched foods and standardized supplements, like SelenoExcell®, are affordable and desirable options.
2. Studying how Se supplementation affects the thyroid in healthy subjects with slightly low Se status has led to conflicting results. Winther and colleagues performed a double-blinded, randomized control trial to tackle this concern.
The trial focused on a Danish population, known to have marginally low Se status (~98.7 mcg/L). A total of 491 subjects, aged 60-74 years, were allocated to supplementation of high-Se yeast at 0, 100, 200, and 300 mcg/day. Measurement of Se, thyroid hormones (TSH, FT3, FT4), and thyroid antibodies in blood samples was done at baseline, 6 months, and 5 years.
The researchers found that with the increase in high-Se yeast dose, an effect in thyroid function was observed as a decrease of TSH and FT4 concentrations. The trial also provided data on the Se status of Denmark’s elderly population (~87.3 mcg/L).
A comparable study performed in the UK did not show the same effects on thyroid function, but the authors point out their population is larger and followed participants for a longer time, yielding more statistical power. However, a similar effect in TSH and FT4 was reported in a 2014 study in UK pregnant women (a).
Considering the U-shape relationship between Se and human health and the findings of the trial, it was noted that increasing Se intake is not recommendable for all individuals with marginal Se status.
This study is relevant as it reminds us how essential it is to develop a personalized approach to Se supplementation, and how the effects of Se deserve more research.
Winther KH, Bonnema SJ, Cold F et al. Does selenium supplementation affect thyroid function? Results from a randomized, controlled, double-blinded trial in a Danish population. Eur J Endocrinol 2015;172:657-67.
(a)Mao J, Pop VJ, Bath SC, Vader HL, Redman CW & Rayman MP. Effect of low-dose selenium on thyroid autoimmunity and thyroid function in UK pregnant women with mild-to-moderate iodine deficiency. European Journal of Nutrition, 2014.
Inside our Thyroid Market Spotlight:
- Formulator's Corner with Jim Roufs, MS, RD: Selenium and Thyroid
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- White Paper: Why Selenium-enriched yeast? Personalized medicine’s most useful mineral
- Product Highlights: Profiles of Ortho Molecular Products’ Thyrotain and Seleno-Iodide
- Good, Better, Best: Turnkey formulation options to meet your specific needs
- Cypress Ingredients to attend Supplyside East 2018, Booth #B138
Author Dr. Mark Whitacre is the Chief Science Officer at Cypress Systems. Dr. Whitacre has nearly two decades of executive management experience in both Fortune 500 and entrepreneurial companies, including broad international experience. Much of his career has been in the area of biotechnology and microbiol fermentation. Dr. Whitacre earned a Ph.D. in Nutritional Biochemistry from Cornell University where he studied under a world-renowned selenium scientist, Dr. G.F. Combs, Jr.