2 The health effects of secondhand
smoke
9. Secondhand smoke (also known as environmental
tobacco smoke, ETS, or 'passive smoking') is produced from two
sources. The first is so-called 'mainstream smoke'; this is smoke
which is puffed by the smoker, inhaled and then exhaled. The second
is 'sidestream smoke', which is released into the ambient air
from the smouldering tip of a lit cigarette between puffs. The
constituents of mainstream and sidestream smoke are similar but
their concentrations differ, in general being higher in sidestream
smoke. The great majority of SHS consists of sidestream smoke.
10. Tobacco smoke contains more than 4,000 different
chemicals, at least 50 of which are known carcinogens. These include
benzo[a]pyrenes, aromatic amines and tobacco-specific nitrosamines.
It also contains nicotine, toxins such as carbon monoxide and
hydrogen cyanide and irritants such as acrolein. SHS consists
of a gas phase and a particulate phase, the former including carbon
monoxide, ammonia, dimethylnitrosamine, formaldehyde, hydrogen
cyanide and acrolein, the latter, the complex of compounds collectively
termed tar, including benzene and benzo[a]pyrene. Nicotine is
present in both the gas phase and the particulate phase.[7]
11. High levels of particulates are found in tobacco
smoke. Dr Richard Edwards, a Senior Lecturer in Public Health
at the University of Manchester, told the Committee:
When you are talking about exposure from particles
which are known to affect health, and there are plenty of studies
to show that particulate matter affects health, some of the places
where you get the very greatest exposure is in the indoor environment
in smoky pubs, much more than you do from traffic pollutants at
the road side.[8]
12. The level of exposure to SHS can be measured
in a number of ways. It is possible to measure directly the concentration
of known constituents of SHS in the air. Surveys and questionnaires
can collect information on a person's duration and frequency of
exposure. Personal monitors can be used to measure exposure to
nicotine or smoke particles. It is also possible to detect the
constituents or metabolites of SHS in hair, blood, saliva or urine.
In this way, the amount of SHS absorbed by a person can be assessed
by levels of biomarkers such as nicotine (and, more usually, its
breakdown product, cotinine) as well as by markers of DNA and
protein damage.[9]
13. Since mainstream and sidestream smoke contain
the same chemicals, exposure to SHS is likely to cause most, if
not all, of the diseases caused by active smoking, but with a
lower absolute level of risk.[10]
Scientific studies have employed two main designs to investigate
the effects of SHS on disease risk for non-smokers:
- The case-control study, which
compares exposure to SHS of people with and without a particular
disease and thereby determines whether people with a disease are
more likely to have been exposed;
- The cohort study, which compares the incidence
of disease in those with and without exposure to SHS prospectively
over a period of time.
Many case-control studies have examined the effects
of SHS by determining whether non-smoking women who have developed
a smoking-related disease are more likely to have lived with a
smoking partner than non-smoking women who do not have the disease.
The focus has been predominantly on women because smoking has
historically been much more common in men than in women.
14. A considerable body of evidence has accumulated
over the last thirty years which has demonstrated with increasing
certainty that exposure to SHS both causes illnesses and exacerbates
existing ill health. In 1983, the Department of Social Services'
Independent Committee on Smoking and Health affirmed a link between
secondhand smoke and ill health, and, in 1988, went on to note
that exposure to SHS could cause several hundred deaths from lung
cancer in non-smokers in the UK each year. In 1986, the United
States Surgeon-General had concluded that exposure to SHS presented
a major risk to health.
15. More recently, the case that SHS is harmful to
public health has been made by the Department of Health's Scientific
Committee on Tobacco and Health. In 1998, it produced a report
which concluded that exposure to SHS was a cause of lung cancer
and heart disease in adults, as well as of a variety of diseases
in children.[11] As a
result, the report recommended restrictions on smoking in public
places, and, where possible, a ban on smoking in the workplace.
In 2004, SCOTH released Secondhand Smoke: Review of evidence
since 1998, in which it concluded that:
- There is an estimated 24% increased
risk of lung cancer in non-smokers exposed to SHS;
- There is an estimated 25% increased risk of heart
disease in non-smokers exposed to SHS;
- Exposure to SHS is strongly linked to an elevated
risk of pneumonia, bronchitis, asthma, middle ear infection, decreased
lung function and sudden infant death syndrome in children.[12]
16. In July 2005, the Royal College of Physicians
(RCP) published Going smoke-free: The medical case for clean
air in the home, at work and in public places, a report on
secondhand smoke by the RCP Tobacco Advisory Group. This study
presented a comprehensive survey of the available scientific data,
as well as examining issues such as public response to potential
smoke-free legislation and the likely health and economic effects
of a ban on smoking in public places. It attempted to quantify
the deaths attributable to SHS in the UK in 2003, and divided
these deaths into those caused by exposure to SHS at home (the
vast majority) and in the workplace.
17. The data were updated from those in a study by
Professor Konrad Jamrozik, a public health specialist at the University
of Queensland, which suggested that SHS caused approximately 12,200
deaths in the UK in 2003, of which a minimum of 500 were due to
smoke in the workplace. Within that subsection, it was estimated
that perhaps 50 deaths were due to smoke in hospitality industry
workplaces. The Royal College of Physicians' report, in recording
these figures, noted that the estimate of 12,200 deaths "is
likely to be conservative".[13]
The study also noted that a large proportion of the deaths occurred
in those aged under 65.
18. Recent evidence has also demonstrated a disturbing
aspect of the epidemiology concerning exposure to SHS, namely
that even low levels of exposure can cause a significant increase
in the risk of heart disease. A cohort study published in the
British Medical Journal in 2004 suggested that the risk of ischaemic
heart disease[14] in
non-smokers who were exposed to SHS was comparable to that in
regular smokers who smoked between one and nine cigarettes per
day. Giving evidence to the Committee, Dr Allan Hackshaw, Deputy
Director of the Cancer Research UK and University College London
Cancer Trials Centre and a specialist in epidemiology and medical
statistics, summed up the issue:
The relationship between passive smoking and
lung cancer is linear, but for heart disease it is not. You only
need a small amount of exposure and that gives you your big risk
of heart disease. That has been shown in lots of studies of active
smokers, as in passive smokers as well.[15]
19. The tobacco industry does not accept the weight
of scientific evidence that SHS is a substantial hazard to the
health of non-smokers. Dr Steve Stotesbury, Industry Affairs Manager
and Chief Scientist for Imperial Tobacco Ltd, told the Committee
that "the scientific evidence, if you take it as a whole—and
that includes the lung cancer, heart disease and chronic bronchitis—is
currently insufficient to establish that other people's tobacco
smoke is a cause of any disease".[16]
He went on to cast doubt on the effect of SHS on the health of
children, saying that there was "insufficient evidence"
to demonstrate a link.[17]
20. Dr Stotesbury drew attention to a study carried
out by Professors James Enstrom and Geoffrey Kabat which was published
in the British Medical Journal in 2003. The study was an analysis
of data collected by the American Cancer Society's Cancer Prevention
Study, which monitored 118,094 Californian adults from 1959 to
1998. In particular, Enstrom and Kabat concentrated on the 35,561
non-smokers who were married to smokers, on the grounds that they
would be exposed to SHS on a regular basis. The study concluded
that exposure to SHS had no significant association with an increased
risk of death from lung cancer or coronary heart disease.[18]
21. However, the study by Enstrom and Kabat has also
been widely criticised. It was funded by the tobacco industry
and supported by the Centre for Indoor Air Research (CIAR), a
now-defunct group founded by, and financially dependent on, tobacco
manufacturers. The methodology has also been questioned, on the
grounds that it does not distinguish sufficiently clearly between
people who were exposed to SHS and those who were not, and that
it was based on a small subset of the American Cancer Society's
data. The Chief Medical Officer, Professor Sir Liam Donaldson,
concluded that Enstrom and Kabat "carried out a study with
a flawed methodology which led them to the wrong conclusions".[19]
22. The central issue, as the Royal College of Physicians'
report stressed, is the importance of examining and analysing
all of the evidence rather than focusing on a single study. It
noted that individual studies are susceptible to bias, but that
systematic overviews and quantitative meta-analysis could address
the problems inherent in the individual studies. Finally, it reported
that "for studies of ETS effects on health there is an overall
consistency within the published literature, derived from diverse
locations and a variety of study designs, which is impressive".[20]
23. Dr Hackshaw went on to summarise the scientific
evidence:
Passive smoking you can think of as a mild form
of active smoking, so it must be associated with some risk. There
are many studies on active smoking. There have also been many
studies in passive smoking in non-smokers. There are over 50 on
lung cancer and they consistently show that the increase in risk
is of the order of 25%. Similarly for the studies of heart attacks:
they consistently show that the risk is of the order of about
25% […] Estimates of the number of deaths were published
in the BMJ [British Medical Journal] recently by Professor Jamrozik.
That was a simple analysis based on various estimates of the prevalence
of exposure, people who are exposed to passive smoke, the increase
in risk associated with four specific disorders and the number
of people who get lung cancer, heart disease, stroke and chronic
lung disease each year, and if those estimates are put together
in a formula you get a rough idea of how many deaths per year
you can expect […] The figure quoted in the report is about
12,000.[21]
The Chief Medical Officer told the Committee that
"any doubts or scepticism about the health impact of secondhand
smoke are resolved scientifically in my view".[22]
He went on:
There have been syntheses of the research evidence
by major international bodies and expert committees that have
reviewed the validity of the research and essentially the risks
to non-smokers of inhaling a smoker's smoke through being exposed
to 50 carcinogens, which is roughly the number of cancer causing
chemicals in cigarette smoke, and to carbon monoxide. There are
both short-term risks of an increased risk of clotting of the
blood and therefore of a heart attack and longer-term risks such
as cancer, coronary heart disease, chronic bronchitis and promoting
asthma attacks in children.[23]
24. We
are convinced by the evidence of experts, including the Chief
Medical Officer, the Royal College of Physicians, SCOTH, the US
Surgeon General and the World Health Organisation, that secondhand
smoke is a serious and preventable cause of death and ill-health.
7 Royal College of Physicians, Going smoke-free:
The medical case for clean air in the home, at work and in public
places, July 2005, ISBN 1 86016 246 0. Back
8
Q 72 Back
9
See, for example, Report of the British Medical Association Board
of Science and Education and Tobacco Control Resources Centre,
Towards smoke-free public places, November 2002, p. 1. Back
10
See Ev 4, 6, 9, 17 and 23, Volume II Back
11
First Report of the Scientific Committee on Tobacco and Health,
March 1998. Back
12
Report of the Scientific Committee on Tobacco and Health, Secondhand
Smoke: Review of evidence since 1998, November 2004; see also
World Health Organisation International Agency for Research on
Cancer, Tobacco Smoke and Involuntary Smoking, IARC Monographs
Volume 83, 2004. Back
13
Royal College of Physicians, Going smoke-free: The medical
case for clean air in the home, at work and in public places,
July 2005, ISBN 1 86016 246 0. Back
14
Also known as coronary artery disease; the accumulation of fatty
deposits on the walls of the coronary arteries, limiting the supply
of oxygen to the heart muscle. Back
15
Q 83 [Dr Hackshaw] Back
16
Q 136 Back
17
Q 147 Back
18
James E. Enstrom and Geoffrey C. Kabat, Environmental tobacco
smoke and tobacco related mortality in a prospective study of
Californians, 1960-98, British Medical Journal, vol 326 (May
2003), p 1057. Back
19
Q 442 Back
20
Going smoke-free, p 26. Back
21
Qq 65-66 Back
22
Q 433 Back
23
Q 434 Back
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