According to a study with mice, restricting calories may boost longevity -- by altering growth hormone and insulin.
Scientists have long known that a very low-calorie diet can increase life span in organisms as diverse as yeast, flies and mice. One of the most puzzling questions in aging research, however, is how it works. If they can figure out the molecular processes underlying the boost in longevity, scientists think they might be able to harness the life-extending benefits without restricting diet.
An adult mouse lacking the ability to respond to the growth hormone (right) has a longer life span than a normal mouse (left). Scientists believe this hormonal change may mimic the life-extending effects of calorie restriction. (Courtesy of Michael Bonkowski.)
A new study offers evidence that a decline in growth hormone and a corresponding boost in sensitivity to insulin may be the reason why mice live longer when they eat less -- and that those two hormones may be critically important in controlling aging and longevity.
The study opens up new questions about the role of growth hormone in aging. In humans, growth-hormone levels decline with age, and artificial growth hormone has been touted as an anti-aging drug. But at least in mice, high levels of growth hormone reduce life span, says Andrzej Bartke, a physiologist at Southern Illinois University School of Medicine, who led the study. And these results suggest that lowering growth hormone in mice can mimic the benefits of calorie restriction without the diet.
Within the last few years, biologists have found that mutating certain genes in lower organisms can make them live longer. These discoveries helped fuel the idea that life span is directly controlled by a genetic program in the body -- a program that scientists may be able to manipulate. But, so far, none of these genes have explained the remarkable effects of calorie restriction.
The current study, published in the May 16 Proceedings of the National Academy of Sciences, examined a line of mice who was resistant to growth hormone, which promotes childhood growth and has several other functions in the body. These mice, who are smaller than normal, lack the growth hormone receptor, a molecule that sits at the surface of cells and binds to growth hormone circulating in the blood. Without the receptor, the body's tissues are deaf to the hormone's signal.
Scientists have previously shown that caloric restriction can increase life span in mice by 25 to 30 percent. In the new study, the researchers found that mutant mice, which lack the growth hormone receptor, live just as long as caloric-restricted mice -- even though they ate a normal amount of food. The results suggest that lack of growth hormone triggers a molecular reaction similar to caloric restriction.
The diet delays or prevents diabetes, cancer, heart disease, and brain atrophy.
Rapamycin, an immunosuppressant, enables elderly mice to live longer.
A trial in humans suggests that calorie restriction can boost memory.
Guest (Jesse C)
I did not as yet read the PNAS article, so I am unsure of what exactly their methods were. However, I would like to see the publishers subject the mutant strain mice to caloric restriction. I would expect this measure to NOT extend the lifespan of the mutants, based on the hypothesis that a lack of the growth hormone receptor is equivalent to a low calorie diet. Simple a way to verify the hypothesis...
Guest (Jacques M)
Both insulin and growth hormone work to promote growth in the body, so it should be no surprise that knocking one or the other out would have the same effect. Their expression is believed to be linked through IGF1, but the exact path has yet to be worked out. It would be interesting to see what happens to this strain when subjected to caloric restriction however.
Guest (Emanuel Bocancea)
Aren't growth hormones being fed consistently to all farm animals raised for the slaughter house (cattle, pigs, chickens, etc)? These animals are 'marketable' after only a fraction of the time required to reach the same mass-level by naturally fed counterparts (e.g. in 3rd world countries). Will FDA step in and change the rules so that no hormones are fed to animals for capital benefit that shortens lives? Imagine the fuel savings when most people will have normal mass.
Guest (Steven Erat)
Scientific American has a very good article online (@ $5.00) for those wanting detailed background, by Mark Lane, George Roth, and Don Ingram of the National Institute of Health, National Institute on Aging.
The Serious Search for an Anti-Aging Pill:
http://www.sciamdigital.com/index.cfm?fa=Products.ViewIssuePreview&ARTICLEID_CHAR=15694C67-2B35-221B-678F8F1433AA8994
See also the Wikipedia entry:
http://en.wikipedia.org/wiki/Caloric_restriction
Guest (Michael Bonkowski)
Thank you Steven! Those are great authors and have written excellent reviews. While I am the author of the the paper in discussion I felt I should mention that Jessie C. nailed the hypothesis, findings, and importantance of this paper. In addition if these are expected results from the IGF-1 longevity hypothesis, then you should appreciate that this is the first mammalian mutant to not respond to the benificail actions of CR.
With respect,
Michael Bonkowski
mbonkowski@siumed.edu
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Guest (Paul McLachlan)
Calorie restriction
If calorie restriction increases life span does it follow that high activiety and the burning of calories reduces life span. Or, is it more to do with limiting the fat content in the body?
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Guest (William Thomas)
Calorie Restriction
It doesn't have anything to do with either. Go have another workout though if it makes you feel better.
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Guest (Bob Seitz)
Calorie Restriction
In calorie-restricted animals, exercise tends to shorten life spans. However, most animals don't suffer from coronary artery disease. Many of us in the Calorie Restriction Society try to get 20-to-30 minutes of aerobic exercise every other day as a compromise between burning calories and maintaining cardiovascular fitness.
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Guest (Steve Koelzer)
CaloRestriction
Who said calorie restriction in humans promotes longevity? Long life runs in families and longs legs run in others. We're just trying to get a leg or two up. Problem is that when you try to stand on the shoulders of rats it just makes you hungry. I say eat the rat meat of the long lived ones! and quit trying to run others over.
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