| Cycling and physical health outcomes |
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A large body of data from prospective cohort studies indicates that participation in cycling is associated with lower risk of mortality from any cause, cardiovascular disease and type 2 diabetes.
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The dose-response relationship is curvilinear with the largest lowering of risks seen when comparing no cycling with moderate levels of cycling. Thus, the largest potential for health gains likely to come from increasing participation amongst those who do not currently cycling regularly, rather than encouraging those who already cycle regularly to cycle more.
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Evidence from prospective cohort studies for an association of cycling participation and cancer incidence and mortality is more mixed, with one major study showing lower cancer risk amongst regular cyclists, but other studies showing no significant association. This may reflect, in part, insufficient statistical power to detect any such associations.
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In prospective cohort studies, there is evidence of a modest association between cycling participation and lower bodyweight (<1 kg difference compared with not cycling) and waist circumference (by ∼0.5 cm). These differences are relatively small on an individual level but may at a population level be sufficient to elicit a public health gain.
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The association between cycling and bone health appears to be neutral at best, and may be negative for high level competitive cycling. Thus, particularly for people at risk of osteoporosis (for example women and older adults), the available evidence suggests that cycling should probably not be the sole form of physical activity undertaken, and should ideally be supplemented with other forms of bone-strengthening weight-bearing physical activities to maximise bone health.
Evidence from a small number of intervention trials indicates that increasing cycle commuting leads to improvements in cardiovascular fitness, but effects on body weight or on biomarkers of chronic disease risk are unclear. |
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The observational nature of the majority of the available data makes difficult to draw firm conclusions about the extent to which the associations between cycling and health outcomes are causal, or the extent to which pragmatic, real-world interventions to increase cycling are likely to induce a sustained impact on health outcomes (or biomarkers of risk for such health outcomes).
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Effects of cycling interventions on health outcomes other than cardiorespiratory fitness are currently unclear, as studies have generally been small, short-term, with insufficient statistical power to detect such effects.
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Large-scale, long-term (at least 1 year duration, ideally longer) interventions trials (ideally randomised) are needed to evaluate the sustained effects of increasing cycling participation amongst those who don't currently cycle regularly on health biomarkers causally related to risk of chronic disease (for example, adiposity, blood pressure, blood lipids, glucose, insulin).
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Such trials would ideally encompass a wide range of demographic groups.
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Such trials will provide evidence of a causal relationship between cycling participation and health outcomes and enable quantification of the extent to which health outcomes can be realistically altered by increasing cycling participation. This is vital evidence for public health decision makers.
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| Cycling and mental health, quality of life and wellbeing |
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In cross-sectional studies, participation in cycling is associated with lower levels of perceived stress, higher levels of commuting enjoyment, better perceived general health and higher perceived quality of life. This is consistent with the wider evidence base on physical activity in general and mental health, quality of life and wellbeing outcomes.
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Cross-sectional and prospective cohort studies suggest that cycle commuting is associated with less sickness absence amongst employees
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It is not known whether associations between cycling and favourable mental health, quality of life and wellbeing are causal. From the available evidence it is not possible to fully exclude the possibility that those with better perceived health or quality of life may be those who choose to cycle more, rather than cycling leading to improvements in these health outcomes.
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It is not known the extent to which pragmatic, large-scale interventions to increase cycling amongst those who do not cycle regularly can produce sustained improvements in mental health, quality of life and wellbeing outcomes.
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Intervention trials (ideally randomised) are needed to evaluate the effects of increasing cycling participation amongst those who don't currently cycle regularly on these outcomes.
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Such trials would ideally be large, encompass a wide range of demographic groups, and long enough to evaluate sustained effects (ideally at least 12 months). These trials will also enable quantification of the extent to which these outcomes can be altered by increasing cycling participation.
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| Risks of cycling associated with collisions and exposure to air pollution |
Collisions
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Risks of collisions with cycling are somewhat higher than driving, but still very low in absolute terms
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The health benefits of cycling are more than 25 times greater than the slightly increased risk of collision risk
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Collision risks are lower where there is good cycling infrastructure and providing physical separation between bicycles and motor vehicles improves safety
Air pollution
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Higher ventilation rates during cycling mean inhalation of air pollution particles can be higher during cycling than driving, but pollution gradients are steep on and near roadways so small changes in position on the road relative to vehicles can have substantial effects on exposure
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Using cycle lanes and lower traffic routes can reduce exposure to air pollution for cyclists
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The health benefits of cycling substantially outweigh the potential risks of increased exposure to air pollution in all but the most extreme air pollution conditions worldwide. Even in Delhi (the most polluted city on the WHO database) undertaking up to 45 min of cycling per day was estimated to provide a net health benefit.
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Collision risks of cycling compared with driving when true like-for-like comparisons are made (for example excluding motorway driving, and off-road cycling such as mountain biking and BMX)
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Risks of cycling in polluted environments for susceptible populations, for example those with respiratory problems are uncertain
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Limitations in modelling risks associated with pollution, for example by only considering long-term average exposure levels, add uncertainty to the risk estimates
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Further studies making better like-for-like comparisons of collisions associated with cycling and other modes of transport
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Studies examining the risks of cycling at different levels of air pollution in populations who may be more susceptible to adverse consequences of high levels of air pollution
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More sophisticated studies modelling the impact of pollution exposure during cycling on health outcomes, taking into consideration varying exposures to air pollution
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| Economic benefits and costs of cycling |
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Replacing car journeys with cycling journeys is likely to be cost saving to the individual. Limited data suggest that overall cost per km travelled, taking into account direct financial outlays, costs of time, health benefits and risks of collisions for cycling is less than half that for car journeys.
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Limited data suggests that increasing cycling amongst employees is likely to be cost saving to employers in terms of lower absenteeism costs.
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Cycling generate has the potential to substantial economic benefits to related to health. For example, economic modelling studies have projected that:
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Increasing cycling to 25% of all journeys in the UK by 2050 would provide over £42 billion in economic benefit (including £35.5 billion due to personal health gains).
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Increasing cycling by 3 km per day and walking by 1 km amongst individuals in urban centres in England and Wales would result in £17 billion in savings to the NHS over 20 years
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Replacing car journeys with cycling would result in economic benefits in terms of lower pollution and emissions
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Losses related to reduced duty and taxation associated with replacing car journeys with cycling are more than an order of magnitude lower than the benefits. It may be cost effective to society to subsidise cycling to increase uptake.
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In 2011, cycling contributed an estimated £2.9 billion to the UK economy
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Investing in cycling infrastructure creates more jobs than the same level of investment for other transport infrastructure
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Economic models of cost-benefit of replacing car journeys with cycling for the individual have only been undertaken in limited settings, and do not currently include key aspects such as personal valuation of safety, potential discomfort and other costs such as insurance.
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Estimates of absenteeism cost savings to employers associated with cycling amongst employees are based on observational estimates in a limited range of occupations, and the extent to which interventions to increase cycling participation would change absenteeism rates are not known. The effects of cycling amongst employees on productivity outcomes other than absenteeism is also not known.
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RCTs which capture the full cost savings to an individual (and employer) and their value of time have not been conducted. This would inform the most worthwhile investment of new cycling initiatives.
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Methodologies such a cost-benefit analyses, conducted from a societal perspective are challenging to conduct and to date few have been fully societal in their assessment of benefits.
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From a behavioural economics perspective, we don't know which attributes predict changes in cycling behaviour of the adult population and what the trade-offs are. For example, are people willing to commute for a longer time to increase their personal health benefits? Are people willing to accept financial incentives to increase their cycling level? Is there a gender balance effect on cycling levels and if so, what do women/men need to incentivise them to increase cycling activity?
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Large-scale, long-term interventions which capture all resource use and costs relating to an individual's cycling behaviours and their health-state would facilitate a more accurate understanding of costs and possible associated benefits.
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Societal cost-benefit analyses detailing the costs and benefits across multiple sectors such as health care, employment, transport, retail and education would generate the full societal picture of increasing cycling.
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Evidence is needed on the attributes (and levels) which predict cycling uptake for women and men along with evidence on the trade-offs between attributes such that initiatives can be optimally designed tailed to increase cycling.
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