Rillamas-Sun's study examined the health records of nearly 37,000 older women participating in the Women's Health Initiative, a long-term study sponsored by the U.S. National Institutes of Health.
The researchers found that about 12 percent of healthy-weight women had become disabled by age 85, requiring a walker or some other assistance for getting around.
By comparison, between 25 percent and 34 percent of obese women were disabled, with incidence rising with the patient's body mass index (BMI), a measurement of body fat that takes height and weight into account.
Overall, a waist circumference greater than 35 inches was associated with a higher risk of early death, along with new diseases developing during the study period and mobility disability, the researchers said.
These findings, while focused on women, should also give men pause, Rillamas-Sun said.
"I do expect that these findings would be similar in men," she said, noting that her study was modeled on a Honolulu-based heart and aging study, which looked at Japanese-American men. "In that study, they showed that men who were leaner in midlife were more likely to survive to late-age and be healthy."
In the second new study, Danish researchers reviewed the health data of nearly 72,000 people to determine the effects of overweight and obesity on heart health.
The investigators found that people who are overweight or obese have a higher risk of heart attack or heart disease even if they do not have other metabolic syndrome risk factors such as high blood pressure, high cholesterol or type 2 diabetes.
In people without metabolic syndrome, heart attack risk increased 26 percent if they were overweight and 88 percent if they were obese, the researchers said. Obese people without metabolic syndrome also had a 45 percent increased risk of heart disease.
These findings show it is never too late to lose weight, Rillamas-Sun said.
"Obesity, even in older ages as this study shows, is a risk factor for numerous negative health outcomes," she said. "There are weight-loss interventions that have been shown to be effective for older populations, and older adults who have lost weight have been shown to have improvements in their health."