Rate of Living Theory of Aging

Do We Have Only a Finite Number of Breaths or Heartbeats?

Smartwatch showing pulse
Smartwatch showing pulse. Getty Images/Guido Mieth/DigitalVision

The rate of living theory of aging states that people (and other living organisms) have a finite number of breaths, heartbeats or other measures, and that they will die once they've used those up.

But don't try to live longer by slowing your metabolism just yet: while the theory is helpful to explain some aspects of aging, it doesn't really hold up under modern scientific scrutiny.

History of the Rate of Living Theory

The rate of living theory of aging may be one of the oldest theories that attempts to describe why organisms (including humans) actually age.

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. The modern version of this theory recognizes that the number of heartbeats does not predict lifespan. Instead, researchers have focused on the speed at which an organism processes oxygen.

There is some evidence, when comparing species, that creatures with faster oxygen metabolisms die younger. For example, tiny mammals with rapid heartbeats metabolize oxygen quickly and have short lifespans, while tortoises, on the other hand, metabolize oxygen very slowly and have long lifespans.

Is There Evidence to Support This?

There really isn't much.

For example, in one study, researchers looked at genetically engineered mice that had a defect in the hypothalamus. The defect caused the mice to overexert, which in theory would "use up" their lifespans faster.

Because the hypothalamus in mice is near the temperature control center, the brains in these mice thought their bodies were overheating, and so they lowered the mice's core temperatures. The results did show that a drop of .6 degrees Celsius extended the life of the mice by 12 to 20 percent, so the mice did live longer with lower body temperatures.

The problem is, we don't know why they lived longer. The lower temperature may have slowed the rate of oxygen metabolism, but it may also have changed a number of other systems and processes in the body.

So we don't know why the mice lived longer, only that they did, and that's not proof of the rate of living theory of aging.

The Bottom Line

In fact, there is little evidence that oxygen metabolism, heartbeat or the number of breaths determine an individual's lifespan.

The theory seems to hold up when smaller species with faster metabolisms (i.e., mice) are compared with larger species with slower metabolisms (i.e., tortoises). However, the theory can only partially explain the differences in lifespan between species, and it cannot explain the most important factor: what determines lifespan within species.

For example, if a person lives 100 years, they will have taken far more breaths, metabolized more oxygen and experienced 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.

So don't go into hibernation just yet. There really isn't 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, so your best bet is still a healthy lifestyle with plenty of exercise, a diet with lots of plants, and a positive, relaxed attitude.

Sources:

Jin K et al. Modern Biological Theories of Aging. Aging and Disease. 2010 Oct 1;1(2):72-74.

Sanchez-Alavez M et al. 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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