Higher metabolism does not imply early death

March 10th, 2009 - 4:46 pm ICT by IANS  

London, March 10 (IANS) A higher metabolism was earlier thought to lead to a shorter lifespan, but that may not be true, according to a new study.
The study led by Lobke Vaanholt of University of Groningen, The Netherlands, found that mice with an increased metabolism live just as long as those with slower metabolic rates.

The theory that fast-living animals die young, known as the rate-of-living theory, was first proposed in the 1920s. The premise is simple: Ageing is the inevitable by-product of energy expenditure. The faster you spend energy, the faster you age, and the sooner you die.

This remained a prominent theory of ageing until recently, when comparisons across broad animal groups cast doubt on it. For instance, birds have significantly higher metabolisms than mammals of similar size, yet birds live much longer.

Vaanholt’s study was designed to test the rate-of-living theory among individuals of one species - in this case, mice.

Vaanholt and her team followed two groups of mice through their entire lives. One group’s environment was kept at 22 degrees Celsius and the other group’s at 10 degrees Celsius.

The colder group had to spend more energy to maintain body temperature, and according to the rate-of-living theory, should therefore die sooner than the warmer group.

But that’s not what happened, said a University of Groningen statement. “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 wrote. “These results strengthen existing doubts about the rate-or-living theory.”

The study was published in the journal of Physiological and Biochemical Zoology.

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