[/quote]I was not aware of this research, thank you and this directly addresses what I was talking about. You say you have a study that a group that is eating more lived longer. When all the mice in this study died, I am curious, did the scientists list what the causes of death were for each respectively? As this would be pretty informative.
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Hi Tyciol,
I apologize if you perceived portions of my post as a personal attack. My intention simply was to remind readers to give proper weight to the consensus opinion of experts as compared with laymen.
1. I'm afraid I do not know the cause of death for each mouse in that study.
If you need some help locating studies within the last decade demonstrating that a lower basal metabolic rate does not cause the life prolonging effects of CR, let me know. Anyway, extreme CR today seems primarily of interest to the scientific community only to the extent of discovering the precise mechanism by which it causes the body to prolong its own lifespan. As you are probably aware, there is an increasing body of evidence that CR's benefits are primarily the result of activating sirtuins, specifically SIRT1. If my memory isn't mistaken, there have been several studies on mice recently comparing the effects of interventions employing resveratrol, or even more effective proprietary compounds containing resveratrol, on one group of mice, and CR on the other, with the life extending results being quite similar. I believe there has been at least one study completed recently in which a combined resveratrol/CR intervention was compared to CR alone, and no greater lifespan increase was reported using the combined intervention. I also believe that studies have been done using resveratrol and CR on mice who had been altered so that certain sirtuins no longer functioned, and these mice did not benefit from CR or resveratrol interventions.
2. Getting back to the study on twins showing differences in telomere length between physically inactive and active identical twins, my hunch is that a study like this wouldn't have been funded or attempted without first demonstrating such results at least once in a study of mice (meaning that variables such as diet, etc.--concerns of yours with the accuracy of the study on twins--could have been precisely controlled). However, I'm only able to read online the very short abstract of the study on twins, and am not willing to subscribe to the journal in which it was published to satisfy my curiousity on this point. Perhaps another poster will do so and be gracious enough to summarize the key points not apparent in the abstract after reviewing the full text of the study. A university student such as
Shephard may have free access to this journal (get on it, Shephard!).
3. Regarding other anti-aging benefits of certain forms of exercise that aren't well known by the general public, many studies have demonstrated sharp increases in growth hormone levels resulting especially from very intense weightlifting using the larger muscle groups, and to a lesser extent, high intensity cardiovascular exercises. Representative early studies include ones performed at U. of VA, Penn State U., and U. of FL--let me know if you want the citations. The National Strength & Conditioning Association (NSCA), among other specialized research bodies, continues to show a keen interest on how GH levels are influenced by exercise, as evidenced by the mountain of recent studies they've conducted in this area, many of which can be reviewed at their website.
Why should we care? Because HGH levels decline as we age, and GH interventions (using injections of GH) have demonstrated profound and fairly broad spectrum anti-aging effects in the elderly, as evidenced by the landmark HGH study published in the
New England Journal of Medicine in 1990. Per this study and follow-ups to it, these benefits include sharp increases in lean muscle mass, decrease in body fat, regrowth of tissue in the heart, liver, spleen, kidney etc. (organs that ordinarily shrink with age), greater cardiac output, superior immune function, lowered blood pressure, stronger bones, younger, tighter and thicker skin, improved memory retention, and faster wound healing.
GH supplementation has also been shown to increase at least average life expectancy in mice, and perhaps may increase maximum life expectancy. In a 22 month study using 52 mice aged 17 months (over 3/4 their average life span) published in 1991 in
Mechanisms of Aging and Development, the mice were separated into two groups of equal size: Group One was given a placebo, and Group 2 was treated with GH. By the 16th month, all of the mice in Group One were dead, with all but two having died from natural causes (two were culled for research purposes); by way of contrast, no mouse in Group Two had died of natural causes by the end of the 22nd month, which was the termination point for the study (4 were culled for research purposes). The GH-treated mice were discovered to have
immune systems characteristic of youthful mice (this ties in with the study on telomere length in twins eventually, so bear with me!). Others studies have shown that GH supplementation can reduce shrinkage of the thymus, and (probably as a result thereof) increase levels of immune factors called cytokines, as well as interleukin 1 and 2, lending further support to the hypostheis that GH supplementation has rejuvenating effects on the immune system.
Sadly, HGH supplementation by injection has proven to be
dangerous in humans (particularly with respect to women), at least in studies that gave a uniform dosage of GH to participants rather than one tailored to each of them personally. It is certainly dangerous at excessive levels, and is associated with acromegaly (gigantism); the problem is that an ideal supplemental dosage for one person may be hazardous for another who naturally has higher GH levels. However, no such adverse effects have been reported for persons who have naturally stimulated their body's own GH output through exercise.
4. Interestingly, fasting also causes sharp increases in GH production. Could this explain why mammals used in CR studies sometimes (often?) show an increase in lean muscle mass as compared to the untreated control group, even when they weren't forced to exercise? This observed increase in lean muscle mass is certainly counterintuitive, as you'd expect it to result only from exercise, and not while on a CR diet.
5. And now I return to the study on twins which is the subject of this thread. It is important to note that
only immune cells were studied; testing of the effect of exercise on the length of telomeres in other types of cells will require further studies. In conclusion, it is interesting to note the age-defying effects on components of the immune system as demonstrated both in GH supplementation studies and the study of telomere length in twins. Keeping in mind that exercise of sufficient intensity causes significantly increased GH ouput, it is likely that the fittest category of individuals in the twins study had elevated levels of GH. But is increased GH level only a non-integral side effect of exercise that had no role in the length of immune cell telomeres, or did it cause the observed difference?
Edited by TianZi, 31 January 2008 - 07:33 AM.