Low body heat lengthens mouse lives.

Mice genetically engineered to have low body temperatures lived significantly longer than mice with normal body temperatures, researchers report.

In previous studies, scientists found that severely restricting the number of calories that mice and other organisms consume can lengthen their life spans.

Animals on these low-calorie diets typically have abnormally cool body temperatures, but researchers weren't sure whether that was simply a consequence of burning fewer calories.

To explore whether a low body temperature itself lengthens an animal's life, Bruno Conti of the Scripps Research Institute in La Jolla, Calif., and his colleagues genetically engineered mice to have a faulty sense of body temperature. The alteration lowered the animals' temperatures by about 0.3 to 0.5[degrees]C below normal for a mouse. The altered mice were given as much food as they wanted, and they maintained normal weight.

The low-temperature mice lived about 15 percent longer than normal mice did, the team reports in the Nov. 3 Science. The researchers are investigating whether lowered body temperatures protect cells from damaging molecules called free radicals--one of the ways that restricting calories is thought to extend life.--C B.