Intended for healthcare professionals


Just one cigarette a day seriously elevates cardiovascular risk

BMJ 2018; 360 doi: (Published 24 January 2018) Cite this as: BMJ 2018;360:k167

Air pollution almost as bad as everyone smoking a cigarette a day

There are profound implications for preventative medicine from the fact that just 1 cigarette a day, like passive smoking and current levels of air pollution, has a third to half the additional CHD risk of smoking 20 a day[1].
Only 15.8% of UK adults smoke[2], so the excess population-weighted risk of active smoking is less than 16% of that of the average smoker. Passive smoking has an even lower population-weighted excess risk, thanks to comprehensive smoke-free laws for public places resulting in large (~15%) drops in hospital admissions for cardiac, cerebrovascular, and lung disease[1].
That leaves air pollution, which is much deadlier than previously thought[3]. In Launceston, Tasmania, wintertime deaths from respiratory disease fell by 28% and cardiovascular disease by 20% when woodsmoke pollution was reduced by 17 ug/m3 PM2.5 in winter. Year round, for men, the reductions were 23% (respiratory) and 18% (cardiovascular)[4].
In Canada, deaths from ischemic heart disease increased by 30% when annual PM2.5 exposure increased by just 10 ug/m3[5]. The increase in hospital admissions for heart attacks in another Canadian study was greatest when the particles came from winter wood heating. On such days, a 10 ug/m3 increase 3-day mean PM2.5 increased hospital admissions for heart attacks by 38% in those aged 65+[6]. In Hong Kong, a 10 ug/m3 increase annual PM2.5 exposure increased the risk of cancer by 22%, including a 42% increase for upper digestive tract cancers and 80% for breast caners in women[7].
Population exposure of 10 ug/m3 PM2.5 above background could therefore cause twice the health damage of current UK smoking levels. The damage from London’s average of 13.7 ug/m3 PM2.5 above background[8] is expected to be even worse. London had extraordinary levels of health-hazardous pollution - 3-day mean PM2.5 of 78 ug/m3 in Kensington and 74 ug/m3 at the Sir John Cass School- on 22-24 January 2017, when about half the pollution was attributed to domestic wood burning[9].
Many people do not realize that the UK’s largest single source of PM2.5 - 37,200 tonnes - is domestic wood burning, representing 2.7 times the 13,900 tonnes emitted by road transport[10]. An eco-labelled wood stove is allowed to pollute as much as 25 ten-year-old diesel trucks. When measured under ideal conditions (good air intake and small pieces of dry wood), real-life emissions of an eco-labelled wood stove were 600 times worse than a small diesel truck[11]. Despite this, Defra’s consultation on domestic burning (open until 27/2/2018) “is not seeking to prevent” the use or installation of new stoves, simply “encourage consumers to switch to cleaner wood burning”[12].
Such strategies have not worked in other countries. Despite extremely strict regulations, and substantial public education on how to burn cleanly, real-life emissions of 5 stoves in Christchurch, NZ, averaged 9.7 g/kg, 12 times worse than the lab test results averaging 0.82 g/kg[13].
Despite the mild climate in Sydney, Australia, the average new wood stove emits more PM2.5 per year than 1,000 petrol cars. Only 5% of households use wood as the main form of heating, yet chemical fingerprinting of particulate pollution showed that 25% of Sydney’s premature deaths from air pollution were from domestic wood heating. Estimated health costs amount to thousands of dollars per stove per year[14].
A New Scientist review in 2017 concluded that “log-burning stoves are harming our health and speeding up global warming”. As well as strokes and heart attacks, the mixture of PM2.5 and toxic chemicals emitted by wood stoves increases the risk of lung diseases, cancers, cot deaths, asthma, Alzheimer's, genetic damage in babies and reduced IQ, anxiety and attention deficit when children start school[15].
Many effects appear to be substantial. Increased exposure of just 1 ug/m3 PM2.5 increased the risk of dementia by 8%, Alzheimer's by 15% and the risk of Parkinson’s diseases by 8%. Increased exposure of 3.5 ug/m3 reduced the volume of white matter in the brain by 6.2 cubic centimetres. Exposure to PM2.5 pollution above the US EPA standard of 12 ug/m3 nearly doubles the risk of cognitive decline and all-cause dementia for most people and quadrupled the risk for those with 2 copies of the APOE gene[15].
Non-polluting heating is readily available. An efficient 5 kW air source heat pump can cost less to buy and install than a 5 kW stove and needs only about 1.1 kWh of electricity (costing about 13 p) to provide 5 kW heat. By contrast, although the nominal emissions limit for a 5 kW stove approved for use in smokeless zones is 6.7 g/hr[16], real-life emissions are expected to exceed 10 g/hr implying health costs of £1.58/hr in inner and £0.90/hr outer London, many times greater than the cost of environmentally-friendly heating[8].
A study of airborne particles in UK cities estimated that wood burning was between 23% and 31% of urban derived PM2.5 in London and Birmingham. Woodsmoke pollution was higher at weekends and in the evenings, but poorly correlated with daily temperature, suggesting that it “is in large part decorative and not being used for primary heating.”[17]
With PM.25 pollution causing more damage to population health than cigarettes, with domestic wood burning the largest single-source of UK PM2.5 emissions and ready availability of affordable, non-polluting, environmentally-friendly alternatives, sensible policies are needed to protect public health.
Can there be any justification for allowing the installation of new stoves with estimated annual health costs (for an average 563 hours a year) of £889 in inner and £510 in outer London? At the very least “polluter-pays” taxes equal to the estimated health costs should be levied.
The health damage from misguided diesel policies continues. Policies on wood stoves will be even more misguided, unless many health professionals participate in the consultation ([12] before Feb 28) and argue for effective regulations to protect public health.

1. Johnson, K.C., Just one cigarette a day seriously elevates cardiovascular risk, 2018, British Medical Journal Publishing Group.
2. Guardian. Smoking rate in UK falls to second-lowest in Europe. Available at: 2017.
3. Robinson, D.L., What makes a Successful Woodsmoke-Reduction Program? Air Quality and Climate Change, 2016. 50(3-4).
4. UTAS. Reduction in air pollution from wood heaters associated with reduced risk of death. University of Tasmania media release. . 2013; Available from:
5. Crouse, D.L., et al., Risk of Non-accidental and Cardiovascular Mortality in Relation to Long-term Exposure to Low Concentrations of Fine Particulate Matter: A Canadian National-level Cohort Study. Environ Health Perspect, 2012.
6. Weichenthal, S., et al., Biomass Burning as a Source of Ambient Fine Particulate Air Pollution and Acute Myocardial Infarction. Epidemiology, 2017. 28(3): p. 329-337.
7. Wong, C.M., et al., Cancer Mortality Risks from Long-term Exposure to Ambient Fine Particle. Cancer Epidemiology Biomarkers & Prevention, 2016.
8. Walton, H., et al., Understanding the Health Impacts of Air Pollution in London. Available at:, 2015.
9. Page, M.L., Wood-burners: London air pollution is just tip of the iceberg. Available at: New Scientist, 2017.
10. NAEI. UK emissions data selector. Available at (select domestic combustion). 2018.
11. Kåre Press-Kristensen, Pollution from residential burning, Danish experience in an international perspective. Available at:, 2016, Danish Ecological Council.
12. Defra. Call for Evidence - Domestic Burning of House Coal, Smokeless Coal, Manufactured Solid Fuel and Wet Wood - 2018.
13. AAQG. New Woodheaters Pollute - 2016.
14. AAQG. Sydney - 2016.
15. AAQG. Health experts advise that current wood heater models are too polluting to be allowed. Australian Air Quality Group. Available at: 2015.
16. Air Quality Expert Group, The Potential Air Quality Impacts from Biomass Combustion. Available at:, 2017.
17. Font, A. and G. Fuller, Airborne particles from wood burning in UK cities. Available at:, 2017.

Competing interests: No competing interests

10 February 2018
Dr Dorothy L Robinson
Adjunct Senior Research Fellow
University of New England
Armidale, Australia