Interactions between selenium and iodine--could this be the key?

[Guest guest]

I found this at iThyroid.com, written by , the website owner.

" 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.

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. "