Even low levels of weekly exercise could help reduce blood pressure and improve fitness, scientists say.
Exercising on just three days a week could have health benefits
Experts say walking for half an hour, five days a week, is the minimum required to achieve health benefits.
But a Journal of Epidemiology and Community Health report from Northern Ireland found walking on just three days a week gave similar benefits.
The finding could encourage those with sedentary lifestyles to take up exercise gradually, the authors say.
This could be helpful as few people currently meet the minimum recommendations for exercise, with many saying they do not have enough time.
Blood pressure drops
The study, led by researchers at Queen's University, Belfast, looked at 106 healthy but sedentary civil servants aged between 40 and 61.
The participants took part in a 12-week exercise programme - some were assigned to do 30 minutes of brisk walking five days a week, others did it three days a week, and the rest did not change their lifestyles.
In all, 93 people completed the study and their blood pressure, weight and hip circumferences, and other indicators of fitness were all measured before and after the 12-week programme.
There were no changes in the non-walking group, but in both walking groups there was a significant drop in blood pressure and waist and hip measurements.
This could reduce the risk of having a heart attack or stroke.
All walkers also had improved overall fitness.
Five days minimum
The authors said such changes were enough to make a difference to an individual's risk of dying from cardiovascular disease.
And they concluded: "The results may encourage people who feel they do not have time to exercise on five days each week to consider finding time to commit to a lower weekly target of exercise."
Dr Mark Tully, lead author of the research at Queen's University said exercising five days a week should still be the minimum goal, as it had greater positive effects on blood pressure.
But he said: "To get to that goal the first hurdle could be to exercise three days a week - it's a more achievable target to build up from.
"And people would still be getting benefits."
But he said more research was needed to assess the long-term effects of these levels of exercise.
Blood pressure could be lowered by even light exercise
Ellen Mason, a cardiac nurse for the British Heart Foundation, said the study was a reminder that blood pressure could be reduced even through simple activities, such as brisk walking.
She said: "As this study suggests, the best results can be achieved through exercising for 30 minutes a day, five times a week.
"However, benefits can also be had from exercising three times a week.
"Doing any physical activity is better than doing none."
And Ken Fox, professor of health and exercise sciences at the University of Bristol, said it was "good news" that exercising three days a week had health benefits, but that exercising five days would still be better.
He said: "The message is to exercise five times a week, so you're doing something most days.
"It would be a mistake to change the recommendations from one study."