Men and older people reap the health benefits of London’s bike hire scheme, according to researchers who modelled how injuries and pollution affect those who cycle.
Data on all users between April 2011 and March 2012, show that 578,607 of them spent 2.1m hours riding the bikes and made a total of 7.4m trips – around 12% of the total number of excursions made by all adult cyclists in the hire zone.
But while the benefits of exercise from cycling can have a big impact on health, cyclists also contend with other negative effects such as breathing in road fumes and – as the spate of London cyclist deaths recently showed – traffic accidents. The researchers, from Cambridge, UCL, the London School of Health and Tropical Medicine and the Polish Academy of Scientists, wanted to work out whether they could calculate a net benefit in disability adjusted life years (DALYs), a measure used to show the number of years lost due to ill-health, disability or early death, for this period.
To measure health benefits, the researchers used a measure called metabolic equivalent of tasks (MET), which assigns a score to different activities per hour carried out. Cycling at less than 10mph, for example, gives you a score of four, but upping pace to 10-16mph gives a score of six to ten. They then looked at the relative risks and associations of physical activity with conditions including stroke, depression, dementia, breast cancer and diabetes and the findings from two large studies into physical activity and mortality, including one 400,000 cohort study.
From the modelling results, published in the British Medical Journal, the biggest health benefit for men was a reduction in coronary heart disease but for women it was a reduction in depression.
Age and injury
But all things not being equal, the researchers wanted to know how much of an impact injuries, deaths and air pollution had on how healthy it was to cycle on a Boris bike. To do this they considered a range of other collected data, including injury and death rates for all cyclists in the cycle zone and pollution figures.
While their findings showed there was still an overall benefit in terms of health and DALYs, they also found that what age and gender you are might affect the size of the benefit.
Around 70% of all cycle trips in the hire zone were made by men, but twice as many women were killed in collisions involving heavy goods vehicles (although women were half as likely as men to be involved in other types of collisions with motor vehicles).
The group also found that the risk of injury from cycling increased with age, the benefits from physical activity increased more rapidly. So overall, they concluded, the benefits of cycling substantially outweighed the harms. However, in younger people between 15 and 29-years-old, the “medium-term benefits and harms were both small and potentially negative,” they said. This was due to the relatively small benefits from being more active among this age group, in an area with relatively high injury risks.
To model the impact of injury on health, the team used information from police injury reports and cycle injury rates. But the researchers said the scheme hadn’t been operating long enough to get a conclusive picture from this – in the period that the researchers measured only one bike hire death was recorded, Woodcock said. So they used information on injury rates across all cyclists in the cycle zone.
“What we did find was a statistically worse result with [ordinary] bikes,” Woodcock said. However, it wasn’t clear why. “We can only make suggestions,” he said. “It could be because the bikes are different, they might be heavier, where they’re ridden, or because drivers treat them differently.”
Something in the air
The researchers also compared potential exposure to PM2.5 air pollution (particles that are small enough to travel between the lungs and considered the biggest health problem) between cyclists and people travelling on the London Underground, where concerns about “Tube dust” have been raised. But the report concluded: “In aggregate across all [types of] trips, the benefit from the averted exposure to PM2.5 in the underground approximately balanced the harms from increased inhalation of pollutants as a result of the higher ventilation rates associated with cycling.”
James Woodcock, a senior research associate at the University of Cambridge and co-author of the study, said that while exposure overground was lower, cyclists breathed in more. The researchers also considered how people had travelled before and after hiring a bike. In other words, you breath in more pollutants when you cycle but it depends where you go before and after.
“There’s very detailed air pollution data on every street in London,” Woodcock said. “We then used them to work out exposure along likely routes … Then you can measure average exposure.”
He added: “The exposure overground is much lower than on the Tube but cyclists have a higher ventilation rate and not all trips would have previously been Tube. So for those trips previously by Tube total inhaled PM falls now the person is cycling while for the non-Tube trips it increases, so the total impact approximately zero.”
Air pollution had only a small overall effect on health impacts for those using the bike hire, the researchers said.
The study is one of the most comprehensive studies of its kind looking at the health impact of a cycle scheme. But modelling of this size involves lots of data and lots of variables.
For example, the lack of enough data on older age group injury risk meant the researchers used cyclist data from the Netherlands, which as an established cycling network, to look at relative risks related to older age. This was “because we don’t have enough senior citizens over 60 cycling,” Woodcock said.
But while “the data isn’t perfect”, he said “what it does give you are indications of likely harms and benefits, what conditions lead to what benefits. It would be a mistake to focus only on DALYs.”
Philip Insall, director of health at cycle charity Sustrans, said the methodology was tested. “As long as we accept this is modelling and there will be some variables then I’m very confident in these findings,” he said. “There’s lots of epidemiology studies that show that shifting from sedentary transport like cars to active transport like bikes has a significant impact on disease.”
He said that while they were very concerned about air quality, there was still much more to know about the level of risk it posed. “The balance is still in favour of the advantages of disease reduction from being physically active … There are obviously risks, which we saw in the horrible accidents in London, but nowhere near as much as using vehicles like cars.”
More than 600 cities worldwide have adopted cycle hire schemes including ones in Paris and Barcelona. But while the scheme in London has been popular, the researchers said the data showed most cycle hire users used the scheme infrequently. So while there was a combined health benefit overall, it’s likely that individuals will still need to cycle more to feel the benefit. And according to the study, compared to other forms of transport on average, cycling reduced estimated journey time by about 20%.