A Longer Life Isn't Always A Healthier One
Researchers at the University of Massachusetts Medical School examined how genetically altered worms spend a greater portion of their lives in relatively sedentary and frail states. The findings, published in the Proceedings of the National Academy of Sciences (PNAS), point out how genes that increase longevity do not necessarily increase healthy lifespan.
"Our study reveals that if we want to find the genes that help us remain physically active as we age, the genes that will allow us to play tennis when we're 70 similar to when we were 40, we have to look beyond longevity as the sole criteria. We have to start looking at new genes that might play a part in 'healthspan," said Heidi A. Tissenbaum, PhD, professor of molecular, cellular & cancer biology and the program in molecular medicine at UMass Medical School, and principal investigator of the study, in a news release.
Various studies have helped scientists identify several groups of genes that control longevity in C. elegans, a nematode used as a model system for genetic studies in the lab, including yeast and flies. Researchers found that the genes carry analogs in mammals.
From this, they worked to challenge the assumption that longevity and health are intrinsically connected. Furthermore, they looked to determine how healthy, long-lived C. elegans mutants behaved as they aged.
"The term healthspan is poorly defined in the lab, and in C. elegans few parameters have been identified for measuring health," said Tissenbaum. "So we set out to create a definition of healthspan by identifying traits that could be easily verified and measured as the worms aged."
The researchers found that as the animals age--either wild types or mutants--they delinked physically. Depending on the mutant worms, despite having longer lifespans, they spent a greater percentage of their lives at less than 50 percent of measured maximum function when compared to wild-type nematodes. Increased lifespan was oftentimes spent in a frail and debilitated state, according to the researchers.
"What this means, is that the mutant nematodes were living longer, but most of that extra time wasn't healthy time for the worm," added Tissenbaum. "While we saw some extension in health as the mutants aged for certain traits, invariably the trade off was an extended period of frailty and inactivity for the animal. In fact, as a percentage of total lifespan, the wild-type worms spent more time in a healthy state than the long-lived mutants."
"This study suggests that there is a separate and unexplored group of genes that allow us to perform at a higher level physically as we age. When we study aging we can no longer look at lifespan as the only parameter; we also have to consider health as a distinct factor of its own."
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