POSTED 1 AUG 2002
If you're old enough to remember the Monkees, you probably recall some wacko prescriptions for extending the lifespan:
Take supplements or hormones.
Eat spirulina algae or some equally disgusting "food" product.
Stay away from work, bosses and other occupational hazards.
Save for the last prescription, none of these helped much when tested in the cold light of the laboratory.
An
elderly Amish couple, looking hale and hearty, in a photo from about 1940.
Courtesy Prints and Photographs Division, Library
of Congress
There is one way to live longer, however, if you're a fruit-fly or a rodent: Eat about 30 percent fewer calories. Reliably, this so-called "caloric restriction" gives the average lab rat extra months to play mah jong with cronies.
A similar caloric reduction is now being tested in two groups of monkeys. Although the diet has not yet, statistically speaking, extended their lifespan, 24 percent of free-eating monkeys have died but only 15 percent of calorically restricted monkeys. The caloric restriction monkeys are also healthier.
Caloric restriction may work, but the monkeys are skinny, slightly cold, and kinda hungry (although they are no more willing to "work" for food -- by unlatching a glass door blocking a food cache -- than control animals).
Baltimore blues
Here's a question: Do the biochemical changes seen
in calorically restricted animals appear among people who live a long
time? Poking through almost 30 years' worth of data from the Baltimore
Longitudinal Study of Aging, George Roth and colleagues at the National
Institute on Aging evaluated three factors as "candidate biomarkers" of
longevity.
Dejargonation station. A "biomarker" is a measurable property that stands for something else. A "candidate" is a brainwashed GI from Manchuria.
Oops. We were reading the wrong script. Let's get
back to the study, to be published tomorrow in the journal Science. The
three candidate biomarkers were skin temperature, and blood levels of
the hormones insulin and DHEAS (dehydroepiandrosterone sulfate).
All of these factors change with aging -- and when monkeys and rodents undergo caloric restriction.
DHEA and DHEAS, both steroid hormones made by the adrenal gland, have reputations for being healthy hormones. Women with high levels, for example, have a low cancer risk, and hormone supplements improve animal immune systems.
Nonetheless, replacing DHEA failed to extend life or improve health among people in controlled experiments.
Still, there were indications that DHEAS is a biomarker of aging. In most primates, the levels decline dramatically with age, but "the rate of decline was reduced" among caloric-restriction animals, says Donald Ingram, chief of the behavioral neurosciences lab at the National Institute on Aging. "Does that mean animals with higher levels of DHEAS will live longer? We don't know, because we haven't finished the [monkey] study, so we sought other places to confirm the surmise."
Courtesy
California Department of Social Services
A relation of correlation
Learning whether lowered skin temperature, reduced
insulin levels, and higher DHEAS levels are biomarkers or just noise in
the system was the point of the research published today. Ingram was one
author of the study.
The answer, simply, was "Yes." Men with any of the biomarkers in the long-term Baltimore research program had lower death rates than other men.
Exactly how much life extension was associated with the biomarkers is unclear, according to E. Jeffrey Metter of the National Institute on Aging, another study author. The goal, he says, was testing the biomarker hypothesis, not measuring benefits.
Don't go overboard
There are other reasons to avoid over-interpreting
the results. Among the things that remain to be learned:
The goal of caloric restriction research is not to promote a diet that few people would tolerate, but to understand why restricting calories works, and then find drugs that give the benefits -- without the constant hunger.
If you follow a calorie-restricted diet, you won't be eating much on any
level. For the rest of us, stay low. Fats are bad, complex carbohydrates
are good, and may the best diet win!
Courtesy USDA
Howzit work?
The working hypothesis is that caloric restriction
puts animals on a pathway favoring survival over growth and reproduction,
says Ingram. "If you think about any organism's use of energy, it's got
to evolve a mechanism for the most efficient use."
When sufficient energy is not available, he adds, the organism "begins to divert energy away from this growth-reproduction strategy. Obviously reproduction when energy is not available is not wise, and it must make decisions about how to use the available energy."
Those decisions, he says, have biochemical ramifications. Organisms under stress may change their shape -- some bacteria, for example, create spores able to survive decades of dry or cold conditions.
Higher organisms may increase production of protective chemicals, such as heat-shock proteins or anti-oxidants, to protect the brain and reproductive organs until conditions improve. "They are saying, 'Let's divert the energy into protecting ourselves,'" says Ingram. "'If we don't do that, we've got no chance of ever reproducing.'"
-- David Tenenbaum
BIBLIOGRAPHY
Biomarkers of Caloric Restriction Predict Longevity
in Humans," by G. S. Roth, et al, Science, 2 Aug. 2002, p. 811.
The Truth about Human Aging, S. Jay Olshansky et al, Scientific American.
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