CRers, and I would bet a few low carbers have lower T3, a hormone that regulates metabolism. So if your temperature has dropped and you're feeling a little cold, don't worry! You could live a lot longer! There has already been a correlation made between people with lower body temperature living longer.

I have a nice axillary temp of 35.3 in the morning...

So do you REALLY want to make your metabolism speed up? People with slower metabolisms should have greater survival, but we don't see it because they eat TOO MUCH! which is outweighing the benefits of having a slower metabolism and less oxidative damage, which is shown to be a major contribor to disease and aging.

Longer-lived Rodents Have Lower Levels Of Thyroid Hormone

The thyroid may play an important role in longevity, with longer-lived rodents showing significantly lower levels of a thyroid hormone that speeds metabolism, a new study has found.

The study further strengthens the theory that the faster an animal's metabolism, the shorter its life, and vice versa, said Mario Pinto, the study's lead author. The thyroid releases hormones that regulate metabolic rate.

"Thyroid hormones are key regulators of metabolism and have been widely implicated to influence longevity," the authors wrote. Pinto will present the study "Differential thyroid hormone activity in rodents with different life spans" at a poster session Oct. 9 at Comparative Physiology 2006: Integrating Diversity. The study was carried out by Pinto and Rochelle Buffenstein, City College of New York.

Thyroid key to metabolic rate

The thyroid gland produces thyroxine (T4) which converts to triiodothyronine (T3) in the presence of iodine. T3 is the active component of T4 and is the key hormone in regulating metabolism, Pinto said. When an animal becomes cold, for example, its body converts T4 to T3 to speed metabolism and warm the body, he explained.

"Mice strains that exhibit extended longevity tend to have lower thyroid hormone concentrations than shorter living strains," the authors wrote. "Significant declines in thyroid hormone correlate well with enhanced maximum lifespan."

The study compared the levels of these thyroid hormones among four groups of rodents with different life spans: mice, guinea pigs, Damara mole-rats and naked mole-rats. Mice live to about three and a half years; guinea pigs live to six years; Damara mole-rats to 15 years; and naked mole-rats to 28 years.

The animals were of different ages, but at comparable points in their life spans. For example, the mole-rats, which live 28 years, were two years old. The mice, which live about 3.5 years, were six months old. The study determined the levels of T3 and T4 for each animal.


T4 levels vary the most

T4 levels varied significantly between all of the groups, with the shorter-lived groups having higher levels of T4 than longer-lived groups. The mice, for example, had twice as much T4 as the Damara mole-rats and had and three times more than that of the naked mole-rats, Pinto reported. There was also a significant difference in T3 levels between the naked mole-rats and the guinea pigs, but not between any of the other groups

"These hormone concentration differences correlate with maximum species lifespan and suggest an important regulatory role of thyroid hormone in longevity," the researchers concluded. However, because T3, levels did not differ significantly among all the groups, further research in this area using larger sample sizes (numbers of rodents in each group) is needed, Pinto said.

The question is though, is it only CR'ers or is it everyone with lower T3 that lives longer? And what if T4 is also low?

I'm not quite sure. From this article it states:

"Researchers found reduced T3 levels - similar to those seen in animals whose rate of aging is reduced by CR - only in the people on calorie restriction diets."

"serum concentrations of two other hormones - thyroxin (T4) and thyroid stimulating hormone (TSH) - were normal, indicating that those on calorie restriction were not suffering from the thyroid disease of clinical hypothyroidism. The findings are published online in the Journal of Clinical Endocrinology and Metabolism."

http://www.emaxhealth.com/8/6095.html

Ok, that's interesting. My free T3 has always been a notch below range.

Do they check your total T3, Matt? Or do they look at free T3?

Having experienced the joy and wonder of low T3, normal and high T3, I choose to die 10 years earlier and have a nice healthy metabolism. Low T3 left me with a heart arrythmia, poor memory, high cholesterol, low blood pressure, slow heartrate, balding, slow reflexes, constipation, indigestion, swollen joints, poor exercise recovery, insomnia, depression, and sexual dysfunction. Life already seems much longer living like that, why would you want an extra 10 years of that?

I'm guessing you mean depressed metabolism from less calories not disease. Having a thyroid condition sucks!

Research shows that children whose mothers had hypothyroidism in pregnancy have lower IQs. Do you think that happens with depressed T3 levels?

nancy; They look at total T3 I believe.

nawchem ; oh wow, I don't have any of those problems =/

I've always had comments on how thick my hair is, especially when I go get it cut. Now my hair is even thicker after doing CR! (better nutrition?). I do have low blood pressure but doesn't cause any symptoms, never had constipation in my life, no problems with joints, low cholesterol of course, I have much better memory(fish oil?), and I do have a slow heart rate of around 50bpm.

Anxiety is one thing that seems to be very prevalent in my family and I've had it on and off since I was around 8 years old. Totally in control now, but when it does come on I one or two palptiations.

But CRONers don't have a diseased thyroid or are not suffering from hypothyroidism, hence normal TSH and T4. But I can totally understand if you had all those symptoms, that would suck!

See here: http://jcem.endojournals.org/cgi/co.../jc.2006-0328v1

Main Outcome Measures. Serum total and free thyroxin (T4), total and free T3, reverse T3, TSH (TSH) concentrations.

I guess it saying the T3 levels of croners are lower, not abnormal. So its a eat less, burn less strategy, with the eating less having the health benefits. Thats kind of interesting though that you can still feel good with lower T3 and not have hypo side effects. So do croners have healthy offspring if they do that whle pregnant?

Sorry to ask this, I know you must have said this before, how did you choose your calorie level for this?