Jack Rejeski of Wake Forest University in Winston-Salem, N.C., and colleagues analyzed data on more than 5,000 people over four years.
The researchers compared people in an intensive weight loss and exercise program with people who did not take part.
"If somebody can lose 7 percent of their body weight, they can experience substantial reductions in disability over a period of a year," Rejeski said in a statement.
Rejeski said people can retain mobility benefits if they remain active and control their weight.
The study was published in the New England Journal of Medicine.
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