The study published in the Journal of the American Medical Association's (JAMA) Archives of Internal Medicine found that though lower blood pressure protected healthier, robust older adults but the same may not be true for their more frail counterparts.
The researchers looked at a nationally representative group of 2,340 adults ages 65 and older.
"As we age, our blood vessels lose elasticity and becomes stiff," Lead author Michelle Odden, a public health epidemiologist at Oregon State University, said.
"Higher blood pressure could be a compensatory mechanism to overcome this loss of vascular elasticity and keep fresh blood pumping to the brain and heart," she said.
The study used walking speed as a measure of frailty.
Participants were asked to walk a distance of about 20 feet at their normal rate. Those who walked less than 0.8 metres per second were defined as slower walkers. Those who walked faster than 0.8 metres per second were in the second group of more robust adults, who also had a lower prevalence of diabetes, coronary heart disease, stroke and heart failure.
The third group included those who were not able to complete the walking test for various reasons, including inability to walk 20 feet.
Odden said the mortality differences between the fast walkers and slow walkers or non-completers can be explained simply