"Studies in humans can be done but they're not going to address longevity and it's a self-selected group," he said. "Monkeys are the closest we can get."
The findings come a day after U.S. researchers reported in Nature that rapamycin, a drug typically given to transplant patients, significantly extended the lifespans of mice.
For more on various aspects of growing older, head to the U.S. National Institute on Aging.
SOURCES: Richard Weindruch, Ph.D., professor, medicine, University of Wisconsin-Madison and investigator, Veterans Hospital, Madison, Wis.; Felipe Sierra, Ph.D., director, biology of aging program, U.S. National Institute on Aging; Marianne Grant, registered dietitian, Texas A&M Health Science Center Coastal Bend Health Education Center, Corpus Christi, Texas; July 10, 2009 Science