Thyroxine (T4) screening level

[LimCH]

My recent blood test shows Thyroid screening ....thyroxine (T4) reading of 57.6 L

Will intake of 150mcg selenium capsules daily help increase level?

[Singoutloud]

Hi LimCH it would be helpful if you could post all of your blood results together with the ranges and any medication you are taking. That way it is easier to get a better idea of what is happening rather than guess and get it wrong.

[shaws Administrator]

Did you have the blood test at the very earliest possible and fast?

We need the all the thyroid results with the ranges in order to answer.

[jimh111]

Selenium will not increase T4 levels.

[Hashihouseman]

Selenium is an essential component of the enzymes that convert T4 to T3. If you had high T4 and very low T3 then Selenium levels would be one of several investigations appropriate. You need to know Free T 3 for a Start.

[jimh111 in reply to Hashihouseman]

Your TSH will tell you if you have selenium deficiency as the pituitary relies upon converting T4 to T3 to suppress the TSH. If you TSH is high, fT4 high and fT3 low then suspect selenium. In some countries iodine deficiency occurs at the same time as selenium deficiency. If there are indications that you are low in selenium you should have your iodine levels checked by a doctor. You should not supplement with iodine as it can do more harm than good if you are not deficient.

If your blood tests indicate hypothyroidism or selenium or iodine deficiency you should get them sorted out by a doctor if you are planning a pregnancy.

[LAHs in reply to jimh111]

Jimh, I'm pretty sure it is the hypothalamus which monitors the levels of T4 and, if it is too high or too low it sends the signal to the pituitary to raise or reduce its output of TSH. In turn, the thyroid sees this value (of TSH) and increases or decreases it's generation of T4 accordingly. While the thyroid can manufacture some T3, conversion (of T4 to T3) doesn't take place until the T4 hits secondary sites like the liver/kidneys/brain. It is at that step when you had better have selenium around which is the enzyme (biological catalyst) for that reaction. It is essential that the T4 to T3 conversion takes place because T3 is the major active hormone. But like you and others have said, it is essential to see blood test results so that we know which chemical is missing and analyze the problem.

BTW 150mcg is a whopping dose, most tables I have looked up say 55mcgs is an average daily intake of Se, but again, we need to see the blood test results. I take selenium by eating 2 Brazil nuts per day. Be careful, there are side effects to taking too much Selenium.

[helvella Administrator in reply to LAHs]

Hypothalamus and pituitary are both affected by thyroid hormone levels.

[jimh111 in reply to jimh111]

LAHs, The feedback mechanism applies to both the hypothalamus and pituitary. The hypothalamus produces TRH which stimulates the thyrotrope in the pituitary to produce TSH. In both cases the feedback mechanism works by T3 binding to receptors that attach to thyroid response elements on the DNA controlling expression. It is T3 binding to the nucleur receptors that has effect, just like in peripheral tissues. (Deiodinase works in a different way). Thus T4 entering the pituitary will have no effect until it is converted to T3. And of course if there is too little selenium to make the deiodinase molecule it will affect both the pituitary and peripheral tissues.

Having said the above it is quite possible that the pituitary will have first pickings of the available selenium and so could stay reasonably stable whilst peripheral tissues lose out. This is just speculation. I don't know of any studies looking at selenium status and TSH, fT3, fT4. Some look at total T3 which is lower but from the patients point of view it is fT3 that matters. Unfortunately most of the research includes iodine deficiency.

To answer the LimCH's original question selenium is unlikely to affect T4 levels. If anyone has concerns about selenium the simplist answer is to eat a brazil nut a day as advised earlier.

[LAHs in reply to jimh111]

Thanks, that is really interesting.

Just a rambling thought but I wonder why there are two sensors for T4 levels? I wonder if one detects gross inadequacy and the other acts like a fine tuner? Maybe one double checks the other. Fascinating.

[helvella Administrator in reply to LAHs]

As I understand, and I have no experience as a brain surgeon, the hypothalamus is rather more inside the brain than the pituitary. That is, we might guess that the hypothalamus is affected by thyroid hormone within the brain, whereas the pituitary is affected by thyroid hormone in the rest of the body (effectively, the bloodstream).

As the brain manages quite a bit of its own conversion of T4 to T3, and the transport of both T4 and T3 into the brain seems to be an active process, there might be some sense to having two sensors!

In a typical modern house, we have one thermostat controlling the temperature of water used as hot water, another for water circulated through the central heating system, and another which detects air temperature and adjusts water flow. (Plus, for many of us, additional thermostats on each and every radiator!)

Achieving steady states in complex systems can require many parts to the control systems.

[jimh111 in reply to helvella]

Great idea about responding to hormone levels in and outside the brain. The anterior pituitary is outside the blood brain barrier, in spite of what some endocrinologists sometimes say!

Also the hypothalamus responds to the brain (e.g. depression) and so there is an extra level of regulation.

[helvella Administrator in reply to jimh111]

And it isn't just me who has thought this...

Evaluation of the sites of opioid influence on anterior pituitary hormone secretion using a quaternary opiate antagonist.

ncbi.nlm.nih.gov/pubmed/166...

[LAHs in reply to helvella]

Yes, thanks helvella, that makes sense. I forgot the fact that one is inside and the other outside of the brain.

[helvella Administrator in reply to LAHs]

It looks to me as if it isn't even that simple! But it seems to work as a first approximation. Maybe.

[Juliatom]

Selenomethionine -200mcg helped me rise FT3 levels but never over range.

[Eddie83]

Unlikely. The main effect of selenium is as a component of the deiodinase enzymes that convert T4->T3. You should post units and ranges with your blood test results .... so long as T4 is in-range, the main thing you need to know is how well you are converting (how high your FT3 is). T4 is the thyroid storage hormone; T3 is the active thyroid hormone that you need for proper metabolism at the cellular level.

[humanbean]

I'm puzzled by the result you have given. I think it must be a Total T4 result rather than a Free T4 result?

Total T4 isn't as helpful to people as the Free T4 result.

And we need reference ranges to put any results into context.