Pensioners with pets spend an average of 30 minutes a day outside when they would otherwise be sat down.
Experts believe the health benefits are so great they say dog walking should be prescribed to keep people fit into old age.
The findings come from a study carried out between 2006 and 2011 in which 3,123 adults with an average age of 69 were asked to wear a pedometer for seven consecutive days and provide information on regular physical activity.
They were also asked whether they owned a dog, and if so, how often they took it for a walk.
One in five said they owned a dog and two thirds said they walked it at least once a day.
The sample spent an average of around 11 hours every day sitting down and tended to be less active when it rained.
Regular dog walkers were less active on rainy days too, but they were still more active on these days than people who did not own a dog.
Their physical activity levels were typically 20 per cent higher, and they spent 30 fewer minutes every day sitting down than did people who didn’t own dogs.
In all, owners who regularly walked their pets were more active and less sedentary on the days with the worst weather conditions than were people who didn’t own a dog on days with the best weather conditions.
Yu-Tzu Wu, of the University of Exeter which carried out the research, said: “Our findings hint at the important additional role of extrinsic motivation, in this case the need for the dog to be exercised even in poor weather.
“Those who walked dogs were consistently more physically active than those who did not regardless of environmental conditions.
“These large differences suggest that dog walking, where appropriate, can be a component of interventions to support physical activity in older adults.”
It is estimated that less than half of all older adults in Britain engage in the recommended weekly quota of at least 150 minutes of moderate physical activity.
The data was gathered from people aged between 49 and 91 from Norfolk as part of the European Prospective Investigation into Cancer and Nutrition (EPIC).
EPIC, which started in 1993, originally aimed to look at the potential links between diet and cancer but has broadened its focus to include the factors associated with long term conditions, disability, and death in middle age and later life.
The research team, which included experts from the University of East Anglia and Cambridge Institute of Public Health, suggest their findings “may have considerable potential to support the maintenance of physical activity in older adults and could form part of exercise on prescription schemes.”
They add: “In cases where dog ownership is not possible but where the functional status allows, dog walking opportunities for older adults who do not own a dog could be organised by local community organisations or charities, and dog walking groups may provide wider wellbeing benefits associated with increased social contact.”