A brisk walk even once a week is enough to significantly reduce the chances of early death, a new study has found.

Analysis showed that weekly gentle exercise, such as walking or gardening, could cut the risk by nearly 20 per cent.

But being active for longer or participating in vigorous sports has additional health benefits, researchers said.

The new study, published online in the British Journal of Sports Medicine, shows that even low-level physical activities are associated with a lower risk of death from heart disease, cancer or any cause.

Meanwhile higher amounts of activity or more vigorous activities - such as running, cycling and competitive sports - are associated with additional health benefits that are not outweighed by the risks of participating in these activities, according to the findings.

Every year, a representative sample of the US population is asked about their health and lifestyle for the National Health Interview Surveys.

The researchers used figures collected through the surveys between 1997 and 2008 to estimate the activity levels of 88,140 people aged 40 to 85, and linked that data with registered deaths up until the end of 2011.

Compared with people who were inactive, those who participated in just 10 to 59 minutes per week of moderate physical activities during their leisure time had an 18 per cent lower risk of death from any cause over the study period - and the health benefits continued to mount as activity levels went up.