Illness, Stress, Fasting, etc. ALL INHIBIT T4 to T3 conversion

[Guest guest]

(I produce high levels of cortisol during the day due to the

perceived stress of my job, thus, the below article is quite

insightful for ME, and will be to many of you!! The solution is to

find your own ways of reducing stress----someone wisely mentioned

meditation. I also practice deep breathing. Illness can also cause

you problems, thus the potential need to take a bit more natural

thyroid during those times. Janie)

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.

STRESS, ILLNESS, FASTING, etc.

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.

http://www.drlowe.com/QandA/askdrlowe/thymetab.htm