Reverse T3

[Guest guest]

MORE THYROID INFORMATION

http://drguberman.com/news.cfm?date_range=8/01/04

Armour and Thyrolar both contain 38 mcg of T4 and 9 mcg of T3. This is 4

parts T4 to 1 part T3 (the exact ratio is 4.22 to 1). Some endocrinologists

now advocate the use of products containing both T4 and T3, but they

recommend a higher T4 to T3 ratio. They prefer a ratio 10 parts T4 to 1 part

T3. The lower T3 content of such products renders them far less effective

than Armour and Thyrolar. In our clinical experience, the treatment outcome

is inferior for patients who use products with the lower T3 content. The

inferior treatment outcome is supported by two recent studies conducted by

endocrinologists.[1][2] The studies showed that patients who added only a

small amount of T3 to their T4 continued to suffer from symptoms, just as

did patients who used T4 alone. The ratios of T4 to T3 the patients used

varied, but most used a higher T4 to T3 ration than in Armour and Thyrolar.

Of course, the endocrinologists restricted the patients' dosages according

to their TSH and thyroid hormone levels, and this almost guaranteed that the

patients took too little thyroid hormone and continued to suffer from

hypothyroid symptoms. If a new dose of Armour contains too little T4 and T3

to benefit you, you’ll have to go through another evaluation period. And

you’ll have to do this again and again until you find what I call your

therapeutic window " —a small dosage range that optimally benefits you without

overstimulating you. That optimal dosage range is highly individual, but

historically, the typical patient’s therapeutic window has been somewhere

between 120 to 240 mg (2 to 4 grains). There’s no way to accurately predict

what your therapeutic window is. Until you find it, you may not improve much

from the Armour. But once you do, you’re likely to feel that the wait was

well worth it.

The thyroid gland secretes mostly T4 and very little T3. Most of the T3 that

drives cell metabolism is produced by action of the enzyme named 5

-deiodinase, which converts T4 to T3. (We pronounce the " 5'- " as " five-prime

" ) Without this conversion of T4 to T3, cells have too little T3 to maintain

normal metabolism; metabolism then slows down. T3, therefore, is the

metabolically active thyroid hormone. For the most part, T4 is metabolically

inactive. T4 " drives " metabolism only after the deiodinase enzyme converts

it to T3.

Another enzyme called 5-deiodinase continually converts some T4 to

reverse-T3. Reverse-T3 does not stimulate metabolism. It is produced as a

way to help clear some T4 from the body.

Under normal conditions, cells continually convert about 40% of T4 to T3.

They convert about 60% of T4 to reverse-T3. Hour-by-hour, conversion of T4

continues with slight shifts in the percentage of T4 converted to T3 and

reverse-T3. Under normal conditions, the body eliminates reverse-T3 rapidly.

Other enzymes quickly convert reverse-T3 to T2 and T2 to T1, and the body

eliminates these molecules within roughly 24-hours. (The process of

deiodination in the body is a bit more complicated than I can explain in

this short summary.) The point is that the process of deiodination is

dynamic and constantly changing, depending on the body's needs.

Under certain conditions, the conversion of T4 to T3 decreases, and more

reverse T3 is produced from T4. Three of these conditions are food

deprivation (as during fasting or starvation), illness (such as liver

disease), and stresses that increase the blood level of the stress hormone

called cortisol. We assume that reduced conversion of T4 to T3 under such

conditions slows metabolism and aids survival.

Thus, during fasting, disease, or stress, the conversion of T4 to reverse-T3

increases. At these times, conversion of T4 to T3 decreases about 50%, and

conversion of T4 to reverse-T3 increases about 50%. Under normal,

non-stressful conditions, different enzymes convert some T4 to T3 and some

to reverse-T3. The same is true during fasting, illness, or stress; only the

percentages change--less T4 is converted to T3 and more is converted to

reverse-T3.

The reduced T3 level that occurs during illness, fasting, or stress slows

the metabolism of many tissues. Because of the slowed metabolism, the body

does not eliminate reverse-T3 as rapidly as usual. The slowed elimination

from the body allows the reverse-T3 level in the blood to increase

considerably.

In addition, during stressful experiences such as surgery and combat, the

amount of the stress hormone cortisol increases. The increase inhibits

conversion of T4 to T3; conversion of T4 to reverse-T3 increases. The same

inhibition occurs when a patient has Cushing's syndrome, a disease in which

the adrenal glands produce too much cortisol. Inhibition also occurs when a

patient begins taking cortisol as a medication such as prednisone. However,

whether the increased circulating cortisol occurs from stress, Cushing's

syndrome, or taking prednisone, the inhibition of T4 to T3 conversion is

temporary. It seldom lasts for more than one-to-three weeks, even if the

circulating cortisol level continues to be high. Studies have documented

that the inhibition is temporary.

A popular belief nowadays (proposed by Dr. Dennis ) has not been proven to

be true, and much scientific evidence tips the scales in the " false " direction

with regard to this idea. The belief is that the process involving impaired T4

to T3 conversion--with increases in reverse-T3--becomes stuck. The " stuck "

conversion is supposed to cause chronic low T3 levels and chronically slowed

metabolism. Some have speculated that the elevated reverse-T3 is the culprit,

continually blocking the conversion of T4 to T3 as a competitive substrate for

the 5’-deiodinase enzyme. However, this belief is contradicted by studies of the

dynamics of T4 to T3 conversion and T4 to reverse-T3 conversion. Laboratory

studies have shown that when factors such as increased cortisol levels cause a

decrease in T4 to T3 conversion and an increase in T4 to reverse-T3 conversion,

the shift in the percentages of T3 and reverse-T3 produced is only temporary.