Exercise Aside, Genes May Ultimately Dictate Seniors' Mobility

Of nearly 3,000 seniors studied, those who exercised stayedhealthier than their couch potato peers, but those born with a certaingene benefited the most from physical activity, said Marco Pahor, M.D.,director of University of Florida's Institute on Aging and themulti-institutional study's senior author.

"To our knowledge, this is the first study to show behavioraland genetic interaction in functioning and aging, and shows people arealready pre-selected, that there are genes that interact with behaviorto affect mobility," Pahor said.

Decreasing mobility, along with lack of muscle strength and adecline in aerobic ability, are common aspects of aging that can leadto loss in quality of life, Pahor said. Understanding the mechanisms ofhow people lose mobility may lead to ways to help people remainindependent longer, he added.

Federal health statistics have shown that about 34 percent ofthe U.S. population aged 70 or older reports difficulty walking aquarter of a mile. These individuals are at much greater risk of movinginto a nursing home or dying over a two-year period, compared withtheir counterparts who do not report trouble walking the distance.

And despite the undisputed benefits of exercise, not everyoneresponds the same, even when they do lead active lives - for reasonsthat have not been entirely clear.

In the current study, researchers assessed seniors in an effortto better understand the relationship between genetic makeup, intensityof physical activity and functional decline. Twice a year throughoutthe four-year study, participants ages 70 to 79 reported their level ofactivity and their ability to walk a quarter mile or up 10 stairs.

Researchers also tested the blood of each study subject toidentify which version of a gene long associated with exerciseperformance they had. About a third of the population possesses the DDgenotype of the gene, named for the angiotensin-converting enzyme, orACE. The rest have the II or ID versions of the ACE gene.

Study participants were categorized according to their exerciseintensity and their genetic makeup. Overall, about 41 percent of studyparticipants became less mobile over the four-year period. Even thoughpeople who exercised were less likely to develop substantial physicallimitations, not everyone received the same benefits, even if theyexercised with the same intensity.

About a third of the seniors engaged in significant physicalexercise including walking and strenuous exercise, and they preservedtheir mobility longer than the 70 percent who engaged in little or nophysical activity. Researchers also evaluated the 8 percent whoreported participating in weight training.

But genetic makeup influenced long-term physical function.Among exercisers, the DD and ID genotypes were more likely to remainfit than those with the II genotype, who developed mobility problems ata 45 percent higher rate, researchers found. No difference in mobilityaccording to genotype was found among non-exercisers, suggestingfunction was influenced by an interaction between exercise intensityand genetic make-up.

In addition, seniors who reported weight training and had theDD or ID genotype displayed the lowest rate of mobility loss in anyexercise category. In contrast, weight trainers with the II genotypedeveloped physical limitations similar to those experienced by seniorswho were relatively inactive.

What differences in body composition the genotype creates alsomay yield clues to what causes mobility limitations to develop withage, and what people can do to stay active, Pahor said. Those with theII genotype, for example, tended to have higher total body fat.

"The good news is that regardless of genotype, the physicallyactive people were at lower risk of losing mobility, suggesting thateveryone should exercise to preserve mobility," said Pahor, a professorand chairman of the College of Medicine's department of aging andgeriatric research.

The study's lead author, Stephen Kritchevsky, Ph.D., aprofessor and director of the Sticht Center on Aging at the Wake ForestUniversity School of Medicine, said that people respond differently toexercise and that the implications of that response may change as theyage.

"In our study, the II genotype is associated with increased fatin the leg muscles," Kritchevsky said. "Now energy storage near musclesmay benefit young athletes engaged in endurance activities, but inolder persons, accumulation of leg fat has been linked to poorer musclefunction and metabolic diseases like diabetes."

The study, funded by the National Institute on Aging and theClaude D. Pepper Older Americans Independence Center and conducted inconjunction with researchers at several other institutions, includingthe University of Tennessee and the University of Pittsburgh, opens thedoor to more research on the interaction of behavior and genes and howthat changes with age, Pahor said.

"This report is one step," he said. "It is necessary to do moreresearch to determine whether there are other genes that may affect thebenefits of physical activity on functioning of older adults."