Cycling to work almost halves the risk of cancer and heart disease, according to new research.
A study of more than 250,000 British people found those who got on their bike were 41 per cent less likely to suffer a premature death.
Their risk of developing a tumour or heart disease was reduced by 45 and 46 per cent, respectively, according to the findings published in The BMJ, compared to those who took a "non active" commute such as the train or bus.
The findings add to mounting evidence of the dramatic benefits of exercise to health.
Meanwhile, people who walked to work were 27 per cent less likely to suffer cardiovascular disease and 36 per cent less likely to die from it.
But it did not protect against cancer - or premature death overall.
The study analysed data from 264,337 participants from UK Biobank, which contains detailed information on adults aged between 40 and 69.
They were asked questions about their usual mode of commuting to work and then followed up for five years.
The new cases of cancer, heart attacks and deaths in that period were assessed and related to their method of transport.
The results suggest policies designed to make it easier for people to commute by bike may present major opportunities for public health improvement.
Dr Jason Gill, of the Institute of Cardiovascular and Medical Sciences at the University of Glasgow, said: "Cycling all or part of the way to work was associated with substantially lower risk of adverse health outcomes.
"Those who cycled the full length of their commute had an over 40% lower risk of heart disease, cancer and overall mortality over the five years of follow up.
"If these associations are causal, these findings suggest that policies designed to make it easier for people to commute by bike, such as cycle lanes, city bike hire, subsidised cycle purchase schemes and increasing provision for cycles on public transport may present major opportunities for public health improvement."
The greater benefits seen with cycling compared with walking may be because cyclists covered longer distances, the intensity of the effort is more and they had higher levels of fitness.
Dr Gill said: "What we have shown is cycling reduces the risk of premature death from all causes, including heart disease and cancer.
"Cyclists get bigger benefits to their health than walkers, and there are probably a number of reasons for that.
"What we need now is a step change in the way we develop transport systems like we have seen in the Netherlands and Scandinavia where cycling is normal and cities are built around it.
"It is the biggest study into modes of commuting and their effect on health than all the previous ones put together and shows conclusively that cycling to work reduces the risk of cancer and heart disease.
"The main benefits to health are seen in middle aged and older people. It is no use doing plemty of physical activity when you are young if you do not keep it up.
"Going to the gym becomes more difficult as we get older because of time constraints so building exercise into your daily routine is a way of getting around this."
Co author Dr Carlos Celis-Morales said: "Walking to work was associated with lower risk of heart disease, but unlike cycling was not associated with a significantly lower risk of cancer or overall death.
"This may be because walkers commuted shorter distances than cyclists - typically six miles per week, compared with 30 miles per week - and walking is generally a lower intensity of exercise than cycling."
A study of 45,000 middle aged Danes last year found those who consistently spent 90 minutes on their bike a week were 24 per cent less likely to develop angina or have a heart attack over the next 20 years.
And those who spent just half an hour cycling a week - even as a leisure activity - had a 16 per cent reduced risk.
The NHS advises that people do 150 minutes of moderate exercise a week, such as walking or cycling, or 75 minutes of strenuous exercise such as running or playing football.
But four out of five Brits fail to achieve the target, fuelling an epidemic of obesity and diabetes.
Walking or cycling as part of the daily commute - or other regular activities such as walking the dog - are considered an ideal way to persuade people to exercise consistently.
Another study that followed 20,000 middle aged and elderly Swedes for a decade found those who biked to work were less likely than non bikers to be obese, have high cholesterol, high blood pressure or pre-diabetes.
Dr Mike Knapton, associate medical director at the British Heart Foundation, said: "It is worrying levels of physical activity in the UK are falling as this is associated with an increasing number of heart attacks, strokes and other conditions - including cancers.
"Commuting to work by walking, or better still, cycling, is a great way to combine physical activity into your normal daily routine.
"This study shows people who cycle to work or walk for two hours a week have a significantly reduced risk of heart attack, stroke, and death.
"It is paramount to make physical activity easier and more accessible if we are to reduce the burden of ill health caused by inactivity.
"Local authorities and workplaces should support this by making using active transport as a means to get to work an easy option."
The findings, published in The BMJ, showed the risk of developing a tumour or heart disease was reduced by 45 and 46 per cent, respectively, compared to those who took a "non active" commute such as the train or bus.