The study, appearing this week in the Proceedings of the National Academy of Sciences, showed that mice at the relatively advanced age of 19 months that were placed on a restricted calorie diet lived 42 percent longer than litter mates who continued to eat a standard diet.
Other studies have shown that young mice put on a low-calorie diet live much longer than mice fed the standard fare. But the new research suggests that it is never too late to enjoy a life-extension benefit by reducing calories.
Stephen R. Spindler of the University of California, Riverside, leader of a team conducting the research, said there is little evidence yet that dietary restrictions will extend human life, but in mice, at least, sensible eating even at older ages clearly has a longevity benefit. He said a 19-month-old mouse is the age equivalent of 60 to 65 years in humans.
Spindler said old mice placed on a restricted calorie diet responded quickly with better health and that eventually the animals lived up to six months longer than litter mates fed the standard diet.
If such findings translate to humans, he said, "this could mean a lot more years and a lot of good years. The mice on caloric restriction lived longer and they are healthier."
Spindler said that while older mice that go on a diet do live longer than those that don't, they still don't live as long as mice that have been on restricted diets for a lifetime. He said mice put on low-calorie diets just after birth have been known to live up to four years, almost twice as long as normal mice and months longer than the aged mice in the new study.
The message, he said, is that sensible eating for a lifetime is best, but there are life span benefits even if the diet is not started until old age.
"This is a very important finding," said Dr. George S. Roth of the National Institute on Aging, one of the National Institutes of Health.
"The dogma has always been that the earlier in life you start a restricted diet, the better it works for extending life," said Roth, a researcher studying the aging process who was not involved in Spindler's research. "This finding suggests that you may get some of the same benefits starting late in life."
Spindler said the study also found that the restricted-calorie diets also slowed the development and advancement of cancer. Death from tumors is very common among aged mice, he said, but the researchers found that tumor growth either started later or was slowed among mice fed limited calories.
The researchers also analyzed how the action of genes changed in mice placed on restricted calorie diets. Spindler said there were changes and that these might be biomarkers of how the restricted diet works to extend life.
"People have been searching for 30 years for biomarkers of the changes that take place during the aging process," said Spindler. He said the new study in mice suggests that by measuring the amount and type of proteins made by the genes scientists could pinpoint the biomarkers of aging.
Once those are known, he said, it would be possible to find drugs that have the same effect on life extension as calorie-restricted diets.
Does this mean that eventually aging could be slowed by taking a pill?
"I am confident that that day will come," said Spindler.
By Paul Recer