Here's Bryan Haycock's opinion:
The Scoop on T2 (3, 5-diiodo-1-thyronine)
Hey Bryan,
What is the scoop on this new T2 fat loss compound (3, 5-diiodo-1-thyronine)? The recommended dose is 50 mcg 1 to 3 times a day. The claims are:
"With T2, thyroid production is effectively increased at both the thyroid receptor site, as well as the mitochondria that are located in certain highly metabolic tissues."
"T2, on the other hand, on a mcg-to-mcg basis, is much less suppressive than T3, something on the order of 1%, meaning you'd have to take 100 times the amount of T2, as compared to T3, to get the same inhibition of TSH. At the same time, T2 is just as metabolically potent, and in some instances more potent than T3 — like with increasing hepatic oxygen consumption and uncoupling mitochondria."
"Bottom line with T2, it has every bit as much horsepower as T3, with minimal side effects. And if you follow the guidelines on the T2 label — 50 mcg 1-3 times a day for no longer than six weeks — you should have no problems after you discontinue use."
The scoop is that Diiodothyronine (T2) is an active iodothyronine very similar to T3. T2 is a metabolite of T3, yet it is metabolically active. I guess the best way to cover this particular question is to deal with the claims being made about T2.
First claim, "With T2, thyroid production is effectively increased at both the thyroid receptor site, as well as the mitochondria that are located in certain highly metabolic tissues."
This is false. Thyroid "production" is effectively decreased due to a reduction in both TSH and T4 levels with supplemental T2.
Second claim, "T2, on the other hand, on a mcg-to-mcg basis, is much less suppressive than T3, something on the order of 1%, meaning you'd have to take 100 times the amount of T2, as compared to T3, to get the same inhibition of TSH."
OK, here is a quote strait out of the research:
"The effects of T2s were compared with those elicited by 3,5,3'-triiodo-L-thyronine (T3) (2.5 microg/100 g BW). The serum TSH level was much greater in hypothyroid rats than in euthyroid ones. T3 administration suppressed TSH by 88% compared to control (i.e, the level in hypothyroid rats); it thus reached a value not significantly different from that seen in the euthyroid rats. 3,5-T2 produced a similar effect, suppressing the TSH level by about 75% compared to control; it thus reached values not significantly different from those of the euthyroid and T3-treated rats."(Life Sci 1998;62(26):2369-77)
According to this research, T3 suppressed TSH by 88% at 2.5 mcg/100g BW and T2 suppressed TSH by 75%. To me that is not much difference! Certainly nothing close to the claim of only 1% difference.
There is however another form of T2 called 3,3'-diiodo-L-thyronine or 3,3'-T2. Now 3,3-T2, as apposed to 3,5-T2, has virtually no effect on TSH. However, it also has virtually no metabolic effect at all. Could it be that the company making claims about T2 has confused research looking at 3,3-T2 with that of 3,5-T2?
The claim continues…"At the same time, T2 is just as metabolically potent, and in some instances more potent than T3 — like with increasing hepatic oxygen consumption and uncoupling mitochondria."
When comparing "potency" of T3 and 3,5-T2 you have to take into consideration the several effects of T3. There are at least 3 receptor types for T3, each one seems to have a distinct effect. For example, just because both T3 and 3,5-T2 may increase hepatic oxygen consumption doesn’t mean they will have identical effects when taken as a dietary supplement. For example, in a study comparing T3, 3,5-T2, and 3,3-T2 it was found that low doses of 3,5-T2 (>20 micrograms/100 g BW/day) had no significant influence on body weights, but significantly decreased TSH and T4 serum concentrations. At a high dose of 200 micrograms/100 g per day, T2 suppressed TSH to 43% and T4 to 29% of control levels. T2 will indeed suppress your thyroid output folks.
On the other hand T3 at only 1-15 micrograms/100 g per day, used as a comparison to T2, had significant effects on TSH and T4 levels, and also on body weight. Fifteen micrograms T3/100 g per day decreased TSH to 44%, T4 to 25%, and body weight to 59% of control levels.
In long term experiments (3 months) a low dose (25 mcg/100 g per day) of T2 suppressed TSH to 60% and T4 to 57% of control levels and had no significant effect on body weight. Conversely, 0.1 microgram/100 g per day T3 had significant effects on body and organ weights as well as pellet intake, but with less TSH suppression.
It is incorrect to say that T2 is just as potent for losing body fat as T3. It is even more incorrect to say that T2 will not wreak havoc with your own thyroid output. Here is what the research has to say about T2 compared to T3, "In vivo, T2 has been shown to suppress TSH levels at doses that do not produce significant peripheral manifestations of thyroid hormone activity. Furthermore, T2 has been shown to produce smaller increments in peripheral indices of thyroid status than does T3, when doses resulting in equivalent suppression of circulating TSH are compared."(J Mol Endocrinol. 1997 Oct;19(2):137-47.) What this means is that, at levels of T2 that cause an equal amount of thyroid suppression as a given level of T3, T2 fails to produce as much thyroid effect as T3. So you get more suppression with less activity.
Last claim, "Bottom line with T2, it has every bit as much horsepower as T3, with minimal side effects. And if you follow the guidelines on the T2 label — 50 mcg 1-3 times a day for no longer than six weeks — you should have no problems after you discontinue use."
Reading between the bottom lines…T2 does not have as much horsepower as T3. T2 appears to be a more selective agonist of the thyroid receptors (TRs), perhaps failing to activate all of the subtypes. This gives 3,5-T2 unique properties. Keep in mind that 3,3-T2 has no properties and marketers must be careful to distinguish between research looking at 3,3-T2 and 3,5-T2.
Am I saying 3,5-T2 has no benefit to bodybuilders? No. I’m just saying it isn’t as perfect as some would have you believe. It may very well have some effect on fat loss if taken at high enough doses. Keep in mind however that you will experience some rebound. I have not used T2 myself as of yet so I cannot give first hand experience. Nor will I write T2 off as worthless until I either use it myself or until I have some of my clients use it. All I can say about T2 is buyer beware, and more importantly, buyer be educated!
"Some" references I used:
1: Moreno M, Lombardi A, Lombardi P, Goglia F, Lanni A. Effect of 3,5-diiodo-L-thyronine on thyroid stimulating hormone and growth hormone serum levels in hypothyroid rats. Life Sci. 1998;62(26):2369-77.
2: Ball SG, Sokolov J, Chin WW. 3,5-Diiodo-L-thyronine (T2) has selective thyromimetic effects in vivo and in vitro. J Mol Endocrinol. 1997 Oct;19(2):137-47.
3: Horst C, Harneit A, Seitz HJ, Rokos H. 3,5-Di-iodo-L-thyronine suppresses TSH in rats in vivo and in rat pituitary fragments in vitro. J Endocrinol. 1995 May;145(2):291-7.
