Dear all,

Selenium has essential roles in the regulation of thyroid hormones. It is no surprise that the thyroid is the organ with the highest content of selenium per tissue unit! Let’s have a look at selenium and its importance in autoimmune thyroid diseases!

How to take selenium naturally?

The main source of selenium is dietary intake. The selenium concentration in both plant and animal foodstuffs is largely influenced by geographical variations of selenium content and bioavailability species in soil and water, and utilization of selenium-enriched fertilizers.

Cereals are the major dietary sources of selenium in most countries, as they tend to be consumed in large amounts, followed by meat, fish, eggs, and dairy products.

Bread and cereals, such as wheat, other grains, soya, and Brazil nuts

Allium family (garlic, onion, leek, and wild leek)

Brassica family (rapeseed, broccoli, cabbage)

Less amounts of selenium can be found in:
Other vegetables (e.g., carrots, peas, beans, potatoes, tomatoes) (maximum 6 µg/g Se) and, fruits (maximum 10 µg/g Se).

In omnivorous people, meat and fish represent the largest proportions of selenium intake. Selenium concentration is relatively high in offal, from heart, kidney and liver, from beef (range 0.55–4.5 µg/g) and, for fish, in cod, shark and canned tuna (1.5, 2.0 and 5.6 µg/g, respectively).

A whole egg has an average selenium content of 15 µg/g, while a cup of milk or yogurt contains approximately 8 µg/g Se.

Selenium is an essential element for humans. But please remind that organic forms of selenium can lead to abnormal and potentially toxic products if in excess. Se deficiency in humans occurs when dietary intake is lower than 40 µg/day, whereas toxicity can be observed at daily levels above 400 µg.

How to measure selenium?

Plasma/serum selenium levels reflect exposure up to a few days and weeks and also allow speciation analysis.

Another approach to evaluate Se exposure is based on measuring plasma levels of selenoproteins, such as SeCys, and primarily involved in antioxidant actions, such as Se-dependent glutathione peroxidase GPx1 and selenoprotein P (SEPP1).

The normal range of serum selenium is quite narrow (90–120 µg/L). So, before and during selenium intake, it is better to measure selenium levels first!

Autoimmune diseases and Selenium

Autoimmune thyroiditis affects up to 5% of the world population, with a major frequency in middle-aged women more so than in men. Graves’ disease and Hashimoto’s thyroiditis are the most common forms of autoimmune thyroiditis.

It is known that patients with thyroid disease (including hypothyroidism, subclinical hypothyroidism, autoimmune thyroiditis, and enlarged thyroid) have reduced selenium levels. So, many trials were established to understand whether selenium supplementation may affect the evolution of thyroid immune diseases. Overall, available studies suggest that selenium supplementation may induce a decrease in circulating thyroid autoantibodies. However, in these studies, patient numbers are heterogeneous, selenium supplements include different forms of selenium, duration of the supplementation is different. So they may not demonstrate a definitive relationship between selenium supplements and thyroid disorders.

Graves’ Disease

Newly diagnosed Graves’ disease patients present low selenium levels. In the literature, higher serum Se levels (>120 µg/L) were associated with disease remission. The average follow-up period of these patients was 20.1 months. Higher selenium levels inversely correlated with TSH receptor autoantibodies (TRAb), suggesting the beneficial effects of selenium on the thyroidal autoimmune process and Graves’ disease outcomes. But if we look at the total of the studies, the data is controversial. The length of the studies, selenium intakes, and forms are different. So, there is no consensus on this topic yet. Most importantly, studies did not generally measure Se baseline levels. Most probably, it is likely that selenium supplements are more effective in Se-deficient patients.

Graves’ Ophthalmopathy

Graves’ ophthalmopathy is an autoimmune inflammatory disorder of the orbit and periorbital tissues, and it is a common finding in Grave’s patients.

Graves’ ophthalmopathy patients present lower selenium levels than subjects without orbitopathy. Severe selenium deficiency is associated with more serious orbitopathy. Probably selenium affects this orbitopathy through its antioxidant actions and its effects on the reduction of proliferation and secretion of pro-inflammatory cytokines in orbital fibroblasts and the release of hyaluronic acid.

In the 2021 guidelines of the European Group on Graves’ Orbitopathy (EUGOGO), selenium supplements are recommended only for mild cases (but not for moderate and severe cases).

Sodium selenite (200 µg per day for 6 months), or
SeMet (100 µg/day) can provide a higher rate of improvement in both quality of life (QoL) and overall ophthalmic outcome, as well as a lower rate of progression towards more severe Graves’ Orbitopathy.

Hashimoto Thyroiditis

Hashimoto thyroiditis (aka chronic lymphocytic thyroiditis) is an autoimmune disease. In this disease, our own lymphocytes invade the thyroid gland and cause hypothyroidism.

Some studies showed lower selenium levels in patients with Hashimoto’s thyroiditis than in healthy subjects. Low selenium levels were also found inversely related to TSH and antithyroid antibody levels. Multiple studies checked thyroid functions and autoantibodies. The results are both supportive and not supportive. There is no consensus about this topic. So, for now, selenium supplements are not recommended to every Hashimoto’s thyroiditis patient. Let’s check positive data in the literature.

In the low selenium population, selenium (100 µg/day for 6 months) significantly reduced the level of antithyroid peroxidase antibodies when administered in newly diagnosed and previously untreated Hashimoto’s thyroiditis patients with euthyroidism or subclinical hypothyroidism.

In another study, administration of 200 µg/day Se yeast tablets for at least 6 months in Hashimoto’s thyroiditis patients improved thyroid autoantibodies and thyroid function by increasing the antioxidant activity.

The “SETI study” showed that short-course Selenium Methionine supplementation was associated with a normalization of serum TSH levels in subclinical hypothyroidism. In half of the patients, normal TSH levels continued for 6 months after selenium withdrawal.

A meta-analysis reported that selenium supplementation decreased levels of thyroid autoantibodies after 3, 6, and 12 months in an LT4 (thyroid hormone)-treated population.

Overall, it seems like low selenium levels are related to an increased risk of developing antithyroid antibodies, and selenium supplementation can reduce autoantibody (TPOAb) titers.

However, there are also many studies observing no improvement in thyroid function after selenium supplementation, especially those lasting over time. Two recent meta-analyses showed insufficient evidence for the clinical efficacy of selenium supplementation for all patients with chronic autoimmune thyroiditis, and the same findings were reported by a previous Cochrane Database analysis of four randomized controlled studies on selenium supplementation in Hashimoto’ thyroiditis subjects.

Selenium Toxicity

Selenium toxicity was reported rarely. The symptoms are nausea, weight loss, dehydration, decreased appetite, low calcium, respiratory distress and sometimes death.

Reference:
Gorini, F., Sabatino, L., Pingitore, A., & Vassalle, C. (2021). Selenium: An Element of Life Essential for Thyroid Function. Molecules (Basel, Switzerland), 26(23), 7084. https://doi.org/10.3390/molecules26237084