Staying fit reduces your risk of both dying from cancer and getting the disease in the first place, research suggests.
In the largest study of its kind, researchers found being active slashes your odds of developing lung cancer by 77 per cent.
And those with bowel cancer reduce their risk of dying from it by an astonishing 89 per cent if they exercise regularly, the research added.
Being active has been shown to boost the health of the heart, lung and immune system health, which may lower the risk of cancer, the scientists believe.
Regular exercise also reduces inflammation in the body, which could trigger some forms of the disease.
The research was carried out by John Hopkins University and led by Dr Catherine Handy Marshal, assistant professor of oncology.
'Our findings are one of the first, largest, and most diverse cohorts to look at the impact of fitness on cancer outcomes,' Dr Handy Marshal said.
'Fitness testing is commonly done today for many people in conjunction with their doctors.
'Many people might already have these results and can be informed about the association of fitness with cancer risk, in addition to what fitness levels mean for other conditions, like heart disease.'
Lung cancer kills more adults in the US than any other forms of the disease and was responsible for 1.8million fatalities last year alone, according to the American Lung Association.
Bowel cancer is the third leading cause of cancer-related deaths in the US and is expected to kill 51,020 people this year, American Cancer Society statistics show.
In the UK, 35,419 people died from lung cancer in 2012, according to the British Lung Foundation. And more than 16,000 people die from bowel cancer every year, Bowel Cancer UK statistics reveal.
Exercise has been shown to help food move through the digestive tract. This reduces the amount of time any harmful chemicals found in human waste are in contact with the bowel, lowering the risk of colon cancer.
Being active also lowers inflammation, which, if excessive, causes cells to divide more often. Uncontrolled cell division can lead to the formation of tumours.
But despite its benefits, only two in five adults exercise for two-and-a-half hours a week as recommended by the NHS, The Times reported. And one in six deaths can be linked to inactivity, according to Public Health England.
To uncover how exercise affects cancer risk, the researchers analysed 49,143 people with an average age of 54. The participants underwent treadmill fitness tests between 1991 and 2009, and were each followed for around seven years.
From the start of the study, 388 of the participants went on to develop lung cancer and 220 had bowel tumours. Of which, 282 lung-cancer patients, and 89 of those with bowel cancer, died.
Results - published in the journal Cancer - revealed the fittest fifth of the participants were 77 per cent less likely to develop lung cancer and 61 per cent less at risk of bowel tumours.
And of those who did develop the disease, the fittest fifth lung-cancer patients were 44 per cent less likely to die, while the most active bowel-cancer sufferers were 89 per cent less likely to pass away from the disease.
The researchers hope future studies will investigate whether improving our fitness influences our cancer or mortality risk.
Source: The Daily Mail