Live Fast, Die ... Whenever?

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It has long been thought that a higher metabolism is connected with a shorter lifespan, but new research in the journal Physiological and Biochemical Zoology has found that mice with increased metabolic rates live just as long as their fellow rodents with slower metabolisms.

The rate-of-living theory, which holds that animals with a fast metabolism die young, was first proposed in the 1920s. The idea is that aging results from expending energy: Those who burn up energy the fastest will age the quickest and die the earliest. But modern scientific comparisons across large populations of animals have cast significant doubt on the theory; for instance, birds have much higher metabolisms than similar-sized mammals, but live much longer.

The new study, led by Lobke Vaanholt of the University of Groningen in the Netherlands and now at the University of Aberdeen, was designed to test the rate-of-living theory among individual members of a species — in this case, mice.

Two groups of mice were tracked through their entire lifespans; one group’s environment was 71 degrees Fahrenheit, the other 50 degrees. According to the rate-of-living theory, because the colder group had to expend more energy to maintain body temperature, the chillier mice should have died sooner.

However …

“Despite a 48 percent increase in overall daily energy expenditure and a 64 percent increase in mass-specific energy expenditure throughout adult life, mice in the cold lived just as long on average as mice in warm temperatures,” the authors write. “These results strengthen existing doubts about the rate-or-living theory.”

The finding jibes with another of Vaanholt’s experiments, in which exercise — rather than temperature — was used to manipulate metabolic rates. Vaanholt’s study found that expending more energy over a lifetime via exercise had no bearing on aging; the sedentary mice lived just as long.

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