Walking for just 2.5 hours a week could add more than seven years to your life, researchers believe.

The study found even half of that is beneficial, with 75 minutes of brisk walking a week enough to extend life by almost two years.

The analysis of the lives of more than 600,000 men and women aged 40 and over also added weight to the idea that it is possible to be fat and fit.

The experts from the US government’s medical research agency and Harvard University crunched the results of six previous long-term studies into health and lifestyle.

The analysis focused on moderate exercise – defined as walking fast enough to break into a sweat but slow enough to hold a conversation.

The benefits were clear, with two and a half hours of brisk walking a week adding 3.4 years to life on average.

Doing twice this added 4.2 years, while walking for seven and a half hours weekly added 4.5 years to life.

The biggest gains were seen in people of a healthy weight, where two and a half hours of moderate exercise a week extended life by more than seven years, the journal PLoS Medicine reported.

However, people of a healthy weight who didn’t exercise could expect to die 3.1 years earlier than obese people who did stay active – a finding that underlines the importance of exercising whatever your weight.

The study also revealed the association between physical activity and life expectancy was similar between men and women, and that black people gained more years of life expectancy than white people.

The relationship between life expectancy and exercise was stronger among those with a history of cancer or heart disease than those with no history of either disease.

Dr. I-Min Lee, the study’s senior author, said: “We must not underestimate how important physical activity is for health – even modest amounts can add years to your life.”