Even low levels of weekly exercise could help reduce blood pressure and improve fitness, scientists say.
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.
Source - BBC