1. Health

Rate of Living Theory of Aging

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Updated March 28, 2007

History:

Perhaps one of the oldest theories of aging is called the rate of living theory. This theory states that people (and other creatures) have a finite number of breaths, heartbeats or other measures. In ancient times, people believed that just as a machine will begin to deteriorate after a certain number of uses, the human body deteriorates in direct proportion to its use.

Modern Version:

The modern version of this theory recognizes that the number of heartbeats does not predict lifespan. Instead, researchers examine the speed at which an organism processes oxygen. There is some evidence, when comparing species, that creatures with faster oxygen metabolisms die younger. Tiny mammals with rapid heartbeats metabolize oxygen quickly and have short lifespans. Tortoises, on the other hand, metabolize oxygen very slowly and have long lifespans.

The Evidence:

There is not a lot. Researchers genetically engineered mice with a defect in the hypothalamus to cause the mice to overexert. Because the hypothalamus in mice is near the temperature control center, the mice's brain thought the body was overheating and lowered the core temperature. The results show that a drop of .6 degrees Celsius extended the life of the mice by 12 to 20 percent. The lower temperature may slow the rate of oxygen metabolism. The problem is that the lower temperature may also change a number of other systems and processes in the body. We don't know why the mice lived longer, only that they did.

How the Theory Holds Up:

There is little evidence that oxygen metabolism, heartbeat or the number of breaths determine an individual's lifespan. The theory can only partially explain the differences in lifespan among species. It cannot explain the most important factor: what determines lifespan within species. For example, if a person lives 100 years, they have taken far more breaths, metabolized more oxygen and had more heartbeats than someone who only lives until 80. What we want to know, from a longevity perspective, is what determines which individuals within a species live the longest.

Bottom Line:

Don't go into hibernation yet. There really is no data that slowing the metabolism extends human life. In fact, a slower metabolism would put someone at risk for obesity and other nutritional-related illnesses. Your best bet is still a healthy lifestyle with plenty of exercise, a diet with lots of plants, and a positive, relaxed attitude.

More on Why We Age

Sources:

Manuel Sanchez-Alavez, Raphaelle Winsky-Sommerer, Maria Concetta Morale, Jacinta Lucero, Sara Brownell, Veronique Fabre, Salvador Huitron-Resendiz, Steven Henriksen, Eric P. Zorrilla, Luis de Lecea, Tamas Bartfai. Transgenic Mice with a Reduced Core Body Temperature Have an Increased Life Span. Science. 3 November 2006: Vol. 314. no. 5800, pp. 825 - 828.

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