Washington, Mar 10: A new study, led by Lobke Vaanholt (University of Groningen, The Netherlands), has cast significant doubt on the theory that a higher metabolism means a shorter lifespan.

In the study, the researchers found that mice with 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 faster you expend energy, the faster you age, and the sooner you die. It remained a prominent theory of aging 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 the birds live much longer.

Vaanholt''s study was designed to test the rate-of-living theory among individuals of one species—mice.

For the study, Vaanholt and her team followed two groups of mice through their entire lives.

One group''s environment was kept at 71 degrees Fahrenheit (22 degrees Celsius), and the other group''s at 50 degrees Fahrenheit (10 degrees Celsius).

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

However, that''s not what happened.

"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. These results strengthen existing doubts about the rate-or-living theory," the authors said.

The study has been published in the journal Physiological and Biochemical Zoology. (ANI)