Every additional hour a day you spend sitting is linked to doubling the risk of being disabled, regardless of how much moderate exercise you get.
Researchers from Northwestern University have said sedentary behaviour is its own risk factor for disability over the age of 60, separate from lack of moderate vigorous physical activity.
The study found that between two 65-year-old women, one sedentary for 12 hours a day and one sedentary for 13 hours a day, the second was 50% more likely to be disabled.
The study focused on a sample of 2,286 adults aged 60 and older from the National Health and Nutrition Examination Survey. It compared people in similar health with the same amount of moderate vigorous activity. Moderate activity is walking briskly, as if you are late to an appointment.
Dorothy Dunlop, professor of medicine at Northwestern University Feinberg School of Medicine, lead the study. She said: "This is the first time we've shown sedentary behaviour was related to increased disability regardless of the amount of moderate exercise. Being sedentary is not just a synonym for inadequate physical activity."
The participants wore accelerometers from 2002-05 to measure their sedentary time and moderate vigorous physical activity. The accelerometer monitoring is significant because it is objective.
The older and heavier people are, the more they tend to overestimate their physical activity. Although previous research has indicated a link between sedentary behavior and disability, self-reports meant the research could not be verified.
The study is published in the Journal of Physical Activity and Health. Rowland Chang, senior associate dean for public health at Feinberg, is a co-author on the paper.
Disability affects more than 56 million people in the US. Defined by limitations in being able to do basic activities such as eating, dressing or bathing oneself, getting in and out of bed and walking across a room. According to the study, disability increases the risk of hospital admission and institutionalisation, while being a leading source of health care costs.
Dunlop added: "It means older adults need to reduce the amount of time they spend sitting, whether in front of the TV or at the computer, regardless of their participation in moderate or vigorous activity."
However, the study does not definitively determine sedentary behavior causes disability, as it only examines data at one point in time. Dunlop explained that it was drew "attention to the fact that this is a potential problem".
To cut down on sitting time, Dunlop suggests standing up while on the phone or at a meeting, parking further away from your destination, walking for short errands and taking the stairs instead of a lift.