'Cool mice' lived 15 per cent longer than mice with normal core body temperatures.

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SYDNEY: Keeping cool might be the secret to a longer life, U.S. scientists say.

In a study published today in the U.S. journal Science, mice whose core temperatures were cooled 0.5 degrees Celsius lower than normal lived 15 per cent longer than mice with normal core body temperatures.

"We wanted to test the hypothesis that reduction of core body temperature could contribute to the beneficial effects of calorie restriction on ageing and longevity," said co-author Bruno Conti of Scripps Research Institute in California.

Previous research has found that caloric restriction, the daily consumption of less than the recommended amount of kilojoules in food, prolongs lifespan in a variety of organisms including humans. The reason why is unclear, but the associated reduction in core body temperature has been proposed as one possible explanation.

"What was not known was if the reduction [in core body temperature] was simply a consequence of calorie restriction or if it also contributed to its beneficial effects. Our studies demonstrate that the latter is true," said Conti.

In the study, Conti and colleagues reduced core body temperature in mice by over-expressing a protein dubbed UCP2 (uncoupling protein 2) in a critical part of the brain - the hypothalamus, where the 'central thermostat' of the body resides.

"Local heat production mimicked an elevation of the core body temperature and activated the thermoregulatory mechanism to reduce it. In other words we fooled the central thermostat," said Conti.

The 'cool mice' ate the same amount of food as the controls, but on average showed an increased energy efficiency and lifespan.

"It proves the principle that modest but prolonged reduction of core body temperature contributes to increased lifespan in mice. It also proves that there are ways to increase lifespan without necessarily undergoing dietary restriction," said Conti.

According to Conti, the results might offer insights into the relationship between caloric restriction, core body temperature and lifespan in humans.

"Such findings are particularly important because they were obtained in mice that, like humans, are homeotherms and regulate their core body temperature to maintain it at constant values at a wide variety of ambient temperatures," said Conti.