"The healthiest people were obese and robust," said the study in the Proceedings of the National Academies of Science, which found that 22 percent of older Americans fit that definition of good health despite higher obesity and blood pressure. They had fewer organ system diseases, better mobility, sensory function and psychological health than others.
They were also the least likely to die or become incapacitated five years into the study, which involved 3,000 people aged 57 to 85. Researchers also uncovered new classes of people at twice the risk of dying or becoming incapacitated in five years. They include those of normal weight who face one key health problem such as thyroid disease, anaemia or ulcers, those who had broken a bone since age 45, and those with poor mental health.
The most unhealthy are those with uncontrolled diabetes and high blood pressure, and who often face challenges getting around and performing daily tasks.
"Instead of policies focused on reducing obesity as a much lamented health condition, greater support for reducing loneliness among isolated older adults or restoring sensory functions would be more effective in enhancing health and wellbeing in the older population," said co-author Edward Laumann of the University of Chicago.
Although cancer caused 24 percent of deaths among people over 55, it "seemed to develop randomly with respect to other organ system diseases," the study said.
Challenging current wisdom:
Obesity had long been considered a leading risk factor for dangerous conditions such as heart attack and stroke. More than a third of Americans -- nearly 79 million people - are considered obese, according to the US Centers for Disease Control and Prevention. However, a number of recent studies have suggested that obesity may not be as bad as once thought, and may even offer protective benefits against certain diseases, a phenomenon known as "the obesity paradox."
Still, current medical wisdom holds that people are healthy if they can avoid heart disease, cancer, diabetes, high blood pressure and high cholesterol levels.
But authors of the new study described a different approach, known as the "comprehensive model" of health and aging, that includes factors such as psychological well-being, sensory function and mobility as essential factors of overall health.
Using this new lens, about half of those considered healthy under the current medical model actually have "significant vulnerabilities that affect the chances that they die or become incapacitated within five years," the study said.
"At the same time, some people with chronic disease are revealed as having many strengths that lead to their reclassification as quite healthy, with low risks of death and incapacity."
The findings suggest that "from a health system perspective, a shift of attention is needed from disease-focused management, such as medications for hypertension or high cholesterol, to overall well-being across many areas," co-author William Dale said.