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Wednesday, February 10, 2010

Does Secondhand Smoke Kill?

By now everyone knows that smoking can kill, but does secondhand smoke really kill and how do we know that?

The National Institute of Health (NIH) has a good resource on Secondhand Smoke, and it is perhaps a good place to start. The NIH starts with a very general description from the National Cancer Institute:

You don't have to be a smoker for smoking to harm you. You can also have health problems from breathing in other people's smoke. Secondhand smoke is the combination of smoke that comes from the burning end of a cigarette, cigar or pipe and the smoke exhaled by the smoker. Secondhand smoke contains more than 50 substances that can cause cancer. Health effects of exposure to secondhand smoke include lung cancer, nasal sinus cancer, respiratory tract infections and heart disease.  There is no safe amount of secondhand smoke. Children, pregnant women, older people and people with heart or breathing problems should be especially careful.

The National Institute of Health and the American Heart Association

Let's dig deeper to see if they are just blowing smoke. Most discussions of secondhand smoke define it in an equivalent manner.  Secondhand smoke is exposure to the smoke that emanates from the lit end of cigarettes, cigars, pipes etc.  To find evidence, I skipped to the part of the website entitled research.  Four articles sourced to the American Heart Association (AHA) are cited. A link is provided to news releases about these articles on the AHA website.  Unfortunately, the news releases do not provide full citations; so the conclusions require us to trust the AHA.

The first study
... is a meta-analysis of 13 studies in which researchers examined changes in heart attack rates after smoking bans were enacted in communities in the United States, Canada and Europe. The researchers found that heart attack rates started to drop immediately following implementation of the law, reaching 17 percent after one year, then continuing to decline over time, with about a 36 percent drop three years after enacting the restrictions.

The second study finds that effects of secondhand smoke are worse in toddlers and children than adults to include cardiovascular effects and that obesity increases these effects. The third study looked at 1,209 women in China.  This study found that the incidence of peripheral artery disease in women who were exposed to secondhand smoke was much greater than those who has not been exposed.  Of these women, the incidence of stroke was also much higher.
In a population-based study of 1,209 women in Beijing, China, researchers found a 67 percent increased risk of PAD in those exposed to secondhand smoke compared to those who were not exposed. 
As for the incidence of stroke and heart disease:
Researchers also found the risk of ischemic stroke increased by 56 percent, while the risk of coronary heart disease (CHD) increased by 69 percent compared to those who were never exposed to secondhand smoke.
The fourth study found that toddlers were most affected from secondhand smoke at home.


Certainly, these studies suggest that secondhand smoke has serious health effects and can even kill, but let's see what the Centers for Disease Control (CDC) have to say.  According to the CDC:
There is no risk-free level of exposure to secondhand smoke. Secondhand smoke causes numerous health problems in infants and children, including severe asthma attacks, respiratory infections, ear infections, and sudden infant death syndrome (SIDS). Some of the health conditions caused by secondhand smoke in adults include heart disease and lung cancer.
The CDC cites several sources to support these claims.  The first source is the Surgeon General's 2006 Report on the Health Consequences of Involuntary Exposure to Tobacco Smoke.

 The Surgeon General's Report
This report is more comprehensive than anything I am going to be able to write.  I recommend reading it, or at least the executive summary.

I provide a few highlights from the report below.

In 2005, it was estimated that exposure to secondhand smoke kills more than
3,000 adult nonsmokers from lung cancer, approximately 46,000 from coronary heart disease,
and an estimated 430 newborns from sudden infant death syndrome. In addition,
secondhand smoke causes other respiratory problems in nonsmokers such as coughing,
phlegm, and reduced lung function. According to the CDC’s National Health Interview
Survey in 2000, more than 80 percent of the respondents aged 18 years or older believe that
secondhand smoke is harmful and nonsmokers should be protected in their workplaces.
 Chapter 6 of the report analyzes the respiratory effects of secondhand smoke in children.  The chapter includes an extensive literature review and synthesis of data from multiple studies.  It finds that the evidence suggests that secondhand smoking is a cause for:
  1.      Lower Respiratory Illnesses in Infancy and Early Childhood
  2.      Middle Ear Disease 
  3.      Respiratory Symptoms and Prevalent Asthma in School-Age Children 
  4.      Adverse effects on Lung Growth and Pulmonary Function

There were also conditions that the evidence was suggestive, but not sufficient to infer that they were caused by secondhand smoke and other conditions for which the evidence was insufficient to show a connection.

Chapter 7 looks at cancer among adults from being exposed to secondhand smoke. Similar to chapter 6, chapter 7 includes an extensive review of the literature and meta-analysis and synthesis of the data. there is also an extensive appendix that summarizes each of the studies the conclusions are based upon.  the conclusions:
  1. The evidence is sufficient to infer a causal relationship between secondhand smoke expo-sure and lung cancer among lifetime nonsmokers. This conclusion extends to all secondhand smoke exposure, regardless of location.
  2. The pooled evidence indicates a 20 to 30 percent increase in the risk of lung cancer from secondhand smoke exposure associated with living with a smoker.
Again, there were several conditions where the evidence was suggestive but not sufficient:

  1. The evidence is suggestive but not sufficient to infer a causal relationship between secondhand smoke and breast cancer.
  2. The evidence is suggestive but not sufficient to infer a causal relationship between secondhand smoke exposure and a risk of nasal sinus cancer among nonsmokers.
Also, there were some conditions where the evidence was inadequate:

  1. The evidence is inadequate to infer the presence or absence of a causal relationship between secondhand smoke exposure and a risk of nasopharyngeal carcinoma among nonsmokers.
  2. The evidence is inadequate to infer the presence or absence of a causal relationship between secondhand smoke exposure and the risk of cervical cancer among lifetime nonsmokers.
Chapter 8 looks at cardiovascular disease from exposure to secondhand smoke.  The approach is similar to the previous chapters: it analyzes the literature and synthesizes conclusions.   It is worth pausing here to quote the introduction of this section because cardiovascular disease is the biggest killer in the United States:
Cardiovascular disease is the leading cause of death in the United States (Hoyert et al. 2006).
Cardiovascular disease includes coronary heart disease (CHD), which causes the most deaths, and stroke, which ranks as the third leading cause of death (Hoyert et al. 2006). In 2003, CHD was responsible for approximately 480,000 deaths and stroke was responsible for approximately 158,000 deaths (Hoyert et al. 2006). Each year, an estimated 1.2 million Americans experience a new or recurrent heart attack, and an estimated 700,000 people suffer a new or recurrent stroke (American Heart Association 2005). Active smoking is one of the most important modifiable risk factors for both CHD and stroke (U.S. Department of Health and Human Services [USDHHS] 2004). This chapter considers the evidence that links secondhand smoke to these two major outcomes as well as to carotid arterial wall thickness, an indicator of the degree of atherosclerosis.
 This section starts by reviewing the conclusions form the 2001 report:

  1. The data from the existing cohort and case-control studies “. . .support a causal association between ETS [environmental tobacco smoke] exposure and coronary heart disease mortality and morbidity among nonsmokers” (p. 356).
  2. Secondhand smoke “. . .is associated with risk for CHD mortality (fatal events), morbidity (non-fatal events), and symptoms. Most of the data on the association with mortality were from cohort studies, but most of the data on the association with morbidity were from case-control investigations. Nonetheless, the magnitude of association is similar in both sets of results”
The 2006 report concludes:

  1. The evidence is sufficient to infer a causal relationship between exposure to secondhand smoke and increased risks of coronary heart disease morbidity and mortality among both men and women.
  2. Pooled relative risks from meta-analyses indicate a 25 to 30 percent increase in the risk of coronary heart disease from exposure to secondhand smoke.
Translation: yes, secondhand smoke kills. They also found:
  1. The evidence is suggestive but not sufficient to infer a causal relationship between exposure to secondhand smoke and an increased risk of stroke.
  2. Studies of secondhand smoke and subclinical vascular disease, particularly carotid arterial wall thickening, are suggestive but not sufficient to infer a causal relationship between exposure to secondhand smoke and atherosclerosis.
In the overall implications, they state:
Cal/EPA has estimated that 46,000 (a range of 22,700 to 69,600) cardiac deaths in the United States each year are attributable to secondhand smoke exposures at home and in the workplace (Cal/EPA 2005).
Chapter 9 looks at respiratory effects in adults.  Again it follows a similar methodology.  In this case, the evidence was sufficient to "infer a causal relationship between secondhand smoke exposure and odor annoyance" and " to infer a causal relationship between secondhand smoke exposure and nasal irritation," but we did not need the Surgeon General to tell us that.

The evidence was suggestive but not sufficient to conclude:
  1. that persons with nasal allergies or a history of respiratory illnesses are more susceptible to developing nasal irritation from secondhand smoke exposure.
  2. a causal relationship between secondhand smoke exposure and acute respiratory symptoms including cough, wheeze, chest tightness, and difficulty breathing among persons with asthma.
  3. a causal relationship between secondhand smoke exposure and acute respiratory symptoms including cough, wheeze, chest tightness, and difficulty breathing among healthy persons.
  4. a causal relationship between second-hand smoke exposure and chronic respiratory symptoms.
  5. a causal relationship between short-term secondhand smoke exposure and an acute decline in lung function in persons with asthma.
  6. a causal relationship between chronic secondhand smoke exposure and a small decrement in lung function in the general population.
  7. a causal relationship between secondhand smoke exposure and adult-onset asthma.
  8. a causal relationship between secondhand smoke exposure and a worsening of asthma control.
  9. a causal relationship between secondhand smoke exposure and risk for chronic obstructive pulmonary disease.
There were several conditions for which the evidence was inadequate.

The Other Side

For those willing to believe sources such as the Surgeon General, the CDC, the American heart Association, and the National Institute of Health, this case should be closed. The strongest indictment of secondhand smoke seems to be the increased risk of cardiovascular disease and coronary heart disease,the biggest killer in the US.

Still the work is not finished without looking for another side. I have no doubt that it is possible to find websites that say secondhand smoke is not bad for health. in fact, one can probably find somewhere a website touting the health benefits of secondhand smoke. Rather than troll through the morass of the Internet, let's look at what Phillip Morris has to say. Phillip Morris has a financial interest in selling more cigarettes; if there were a case to be made that secondhand smoke was safe, certainly they would provide that data.

the website of Phillip Morris proclaims:
Phillip Morris U.S.A is the nation's leading cigarette manufacturer and for more than 20 consecutive years has had the highest revenues, income, volume, and market share in the US cigarette business.
 Here is what they have to say about secondhand smoke:
Public health officials have concluded that secondhand smoke from cigarettes causes disease, including lung cancer and heart disease, in non-smoking adults, as well as causes conditions in children such as asthma, respiratory infections, cough, wheeze, otitis media (middle ear infection) and Sudden Infant Death Syndrome. In addition, public health officials have concluded that secondhand smoke can exacerbate adult asthma and cause eye, throat and nasal irritation.

Philip Morris USA believes that the public should be guided by the conclusions of public health officials regarding the health effects of secondhand smoke when deciding whether to be in places where secondhand smoke is present, or if they are smokers, when and where to smoke around others. Particular care should be exercised where children are concerned and adults should avoid smoking cigarettes around them.

We also believe that the conclusions of public health officials concerning environmental tobacco smoke are sufficient to warrant measures that regulate cigarette smoking in public places. We also believe that where cigarette smoking is permitted, the government should require the posting of warning notices that communicate public health officials' conclusions that secondhand smoke causes disease in non-smokers.
 Case closed.



ghasnain said...

How dangerous is second hand smoke compared to first hand smoke? For example, if I am a non-smoker living my whole life with my twin who is a regular cigarette smoker, how much shortening of my natural life should I expect due to second-hand smoke, compared to what my twin might expect from direct smoking? Given that on average I will be inhaling smoke that is diluted by a factor of 1000 or more relative to what my twin inhales while smoking.

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