Slenium and Iodine Interactions- Important

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INTERACTIONS BETWEEN SELENIUM AND IODINE

April 27, 1999

This article was posted at www.ithyroid.com and we thank the author, ,

for his excellent research. The article has since been taken down, and we

have been unable to reach the author to request his permission, but we

respectfully give credit to the source.

According to the manufacturer, Thyodine contains about 40 mcg. (micrograms)

of iodine per tablet. The manufacturer has now added 50 mcg. of selenium per

tablet. Thyodine now contains a relatively balanced amount of selenium and

iodine. We recommend a total daily intake of 200-400 mcg./day of selenium,

depending upon body size.

Selenium and iodine are two minerals which are critically important in the

proper functioning of the thyroid. While the importance of iodine has been

known a long time, the importance of selenium has only been discovered and

explored since 1990. Much research is presently being conducted on the

functions of these two minerals in thyroid function and it is becoming clear

that there is an interaction between the two. Iodine has a seemingly simple

role in the thyroid-it is incorporated into the thyroid hormone molecule.

A deficiency of iodine will cause hypothyroidism and if this is severe and

occurs during pregnancy, the offspring will be mentally damaged and is

called a cretin. Cretinism, or myxeodematous cretinism as it is sometimes

called, is not only caused by an iodine deficiency, but is also influenced

by a selenium deficiency. Iodine apparently has just one function in the

body-in the thyroid.

Selenium, on the other hand, performs many functions. At the beginning of

the 1990s it was discovered that the deiodinase enzymes which convert T4

(thyroxin, the thyroid prohormone) into T3 (triiodothyronine, the cellularly

active hormone) and also convert T3 into T2, thereby degrading it, are

selenium enzymes (formed with the amino acid cysteine). This discovery has

led to a lot of research studies on the effects of selenium, iodine, and

their interactions.

Selenium also performs other important roles in the body. The most important

of these is probably as its role as the body's best antioxidant

(anti-peroxidant). It performs this role as part of glutathione peroxidase

(GSHPx or GPX). As part of GPX, selenium prevents lipids and fats from being

peroxidized (oxidized), which literally means that it prevents fats from

going rancid (this can be seen on your skin as " age spots " or " liver spots "

(autopsies show that skin " liver spots " are accompanied by similar spots of

peroxidized fats in the liver.) Therefore selenium protects all of the

cellular membranes, which are made up of fats, from peroxidation.

Peroxidation of cellular membranes reduces the ability of the membrane to

pass nutrients including minerals and vitamins, so selenium deficiency is

the first step toward developing the many problems caused by nutrient

deficiencies.

Wallach considers a selenium deficiency combined with high intake of

vegetable oils (salad dressings, margarine, cooking oils) as the " quickest

route to a heart attack and cancer. " It seems that the body uses a lot of

selenium to protect the fats from peroxidation. Polyunsaturated fats which

are hydrogenated or heated become the same as rancid fats and large amounts

of selenium are then needed to protect the body. Consumption of these

dietary fats can thus lead to a selenium deficiency.

Selenium is also essential for the production of estrogen sulfotranserfase

which is the enzyme which breaks down estrogen. A deficiency of selenium can

thus lead to excessive amounts of estrogen, which may depress thyroid

function, and also upset the progesterone-estrogen balance.

Wallach also lists other effects of selenium deficiency: anemia (red blood

cell fragility), fatigue, muscular weakness, myalgia (muscle pain), muscular

dystrophy (white muscle disease in animals), cardiomyopathy (sudden death in

athletes), heart palpitations, irregular heartbeat, liver cirrhosis,

pancreatitis, Lou Gehrig's and Parkinson's diseases (mercury toxicity),

Alzheimer's Disease (high intake of vegetable oil), sudden infant death

syndrome (and possibly " breathlessness " in adults, jj), cancer, multiple

sclerosis, and sickle cell anemia.

Selenium is essential for the production of testosterone. A deficiency seems

to be involved in osteoarthritis. I've found studies linking selenium

deficiency to alopecia (hair loss) and to degeneration of the knee joint

(seen in Kashin-Beck disease). Since selenium is necessary to produce GPX

which is a major detoxifier of man-made and environmental toxins, selenium

deficiency can lead to chemical and drug sensitivities.

These are some of the non-thyroidal effects of selenium deficiency. The

effects of selenium deficiency on thyroidal health is even more interesting.

One study I read indicated that in experimental animals, selenium deficiency

will increase T3 in the heart. This may be the reason that selenium

deficiency causes heart palpitations and rapid heart beat, which is common

in thyroid disease.

While we've seen that selenium deficiency will interfere with T4 to T3

conversion and lead to functional hypothyroidism (low T3 phenomenon),

selenium plays another vital role in the thyroid as part of GPX. During the

production of thyroid hormone, hydrogen peroxide (H2O2) is produced. H2O2 is

important for the production of thyroid hormone, but excessive amounts lead

to high production of thyroxin (T4) and also damage to the cells of the

thyroid. GPX plays the extremely vital role of degrading H2O2 and thereby

limiting hormone production and preventing damage to the thyroid cells. This

seems to be the main way in which selenium protects the thyroid from

sustaining damage which can lead ultimately to cancer.

Without selenium, the thyroid gland becomes damaged and it is through this

mechanism that the main selenium and iodine interactions are found. An

iodine deficiency will cause goiter, an enlargement of the thyroid gland

produced by the body in an attempt to increase hormone production from

limited amount of iodine. Selenium deficiency increases the weight of the

thyroid in experimental animals, and a selenium deficiency combined with an

iodine deficiency leads to a further increase in thyroidal weight (bigger

goiter). In African countries like Zaire, there are areas where both iodine

and selenium are very scarce in the soil (these deficiencies seem to run

parallel in most areas). Consequently a high percentage of the people have

goiters and hypothyroidism. An experimental attempt was made to correct the

selenium deficiency and the result was that the hypothyroidism was made

WORSE in the hypos and it produced hypothyroidism in some euthroid subjects.

This was entirely unexpected and the experimenters issued a warning about

supplementing with selenium (and not iodine) when both deficiencies exist

concurrently.

The body has a compensatory mechanism to maintain T3 levels when iodine is

deficient--it increases the production of the deiodinase Type I enzyme

(DI-I). This is not a small increase, but has been shown in cattle to be an

increase of 10-12 times. This increase in ID-I increases the conversion of

the existing T4 to T3 to maintain T3 levels, but also increases the

conversion of T3 to T2 (the degraded by-product of T3). Because of the

iodine deficiency, T4 is not replenished and T3 ultimately decreases from

the lack of sufficient T4 leading to a worsening of the hypothyroidism.

This result is made worse by another phenomenon which hasn't been thoroughly

studied: a selenium deficiency causes an iodine deficiency to get worse.

This may be a protective adaptation by the body to limit the damage caused

to the thyroid when selenium is deficient and iodine is adequate. Let's

examine this part of the interaction.

We've all heard that many doctors tell hypo patients, especially those with

Hashimoto's thyroiditis, not to take iodine because it can aggravate their

condition. The reason seems to be that selenium protects the thyroid gland

from oxidative damage and this damage can increase significantly if iodine

is supplemented. Taking iodine will increase thyroid hormone production and

the production of H2O2 which damages the thyroidal cells. The lack of

selenium prevents GPX from being able to protect the cells from this

oxidative damage. While I doubt if most doctors realize why iodine should be

restricted (it certainly seemed counter-intuitive to me at first), they have

learned through experience that iodine can increase the thyroid damage in

Hashimoto's. The information that selenium should be supplemented along with

iodine is so new that most of them are unaware of it.

Here's what we have: Studies have shown that if iodine is low, selenium must

also be kept low to prevent the hypothyroidism from becoming worse (from

increased DI-I and T4 depletion, as explained above.) So if both minerals

are low, then the person is hypo and gets a goiter, but the damage to the

thyroid is kept to a minimum. More severe problems happen when either

selenium or iodine is high and the other is low. If selenium is high and

iodine low, then T4 to T3 to T2 conversion is accelerated without T4 being

replenished, leading to a worsening of the hypoT. If iodine is high and

selenium is low, then H2O2 is not degraded by GPX. Since H2O2 drives the

thyroid hormone production, then the thyroid over-produces thyroid hormone

(Grave's hyperthyroidism), the thyroid is damaged from the oxidation by the

H2O2, and the end result is that the damaged thyroid ultimately decreases

activity and hypothyroidism results (Hashimoto's thyroiditis). This could

explain the observed progression of Grave's to Hashimoto's.

If a selenium deficiency causes an iodine deficiency, leaving you both

selenium and iodine deficient, and supplementing with either selenium or

iodine causes severe problems, then the only solution is to supplement both

selenium and iodine simultaneously and gradually. Even then you could

experience an immediate boost (from increased conversion of T4 to T3) with a

subsequent letdown (lack of T4 production because of insufficient iodine or

other necessary nutrient). You have to be prepared to ride out the tough

times and continue increasing the selenium and iodine until those two

deficiencies are corrected and the respective metabolic pathways are back

working properly.

Everything that I've read about selenium indicates that it is absolutely

essential for proper functioning of the thyroid. A deficiency of selenium

may lead to either hyperthyroidism or hypothyroidism. I've always wondered

if high intake of selenium can lead to hyperthyroidism and finally found

someone who did the experiment. They found that a high intake of selenium

will not increase T4 production and lead to hyperthyroidism.

If a person has hyperT, then it looks like taking selenium without iodine

will result in a decrease in production of T4 (although there may be an

initial transient increase in T4 to T3 conversion and hence higher T3). I

would suggest to start with a small amount of selenium methionine (about 50

mcg) and gradually increase it. I cannot see any way that thyroid function

can be normalized without selenium.

For hypos the important message is that a selenium deficiency may cause an

iodine deficiency, so that even though you are taking iodine you may not be

assimilating it unless selenium is also being taken. This would explain how

people can have iodine deficiencies even though salt and many foods have

iodine added. Supplement with both iodine and selenium. I would recommend

starting with 100 mcg of selenium and one kelp tablet and gradually work up

to 400-600 mcg of selenium and 2-4 tablets of kelp. [Note from the Green

Willow Tree: Our research indicates that there is an upper safety limit of

400 mcg./day for selenium, and we do not recommend taking more than that

amount. Also, kelp is extremely high in iodine, which is good for the short

term. However, excess iodine consumption long term can actually depress

thyroid function. Dulse, bladderwrack, and Irish moss--the seaweeds found in

Thyodine--are safer, in our opinion, for long term use.]

While I've found research on the interactions of iodine and selenium, there

are two other minerals which need to be studied for their interactions with

these two: zinc and copper. I found one study which examined the complex

interactions of selenium, iodine, and zinc (there are interactions), but

none which have looked at all four minerals in a 4 X 4 factorial design. Now

that would be an interesting study! Hopefully someone will do that soon.

I think one lesson from studying the interactions of selenium and iodine is

that the interrelationships between minerals are very complicated.

Supplementing with one or two can cause further problems. You have to make

sure that you correct every deficiency. Health is built from a chain of

nutrients and, like a chain, health cannot be accomplished if one nutrient

is missing. Sometimes it's complicated putting the chain back together

without running into problems (like supplementing with either selenium or

iodine, but not both), but every deficiency has to be corrected. --

The information in this article is for educational purposes only, and is not

intended as medical advice.

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