Wednesday, May 1, 2013

Does Tobacco Smoking Trigger Asthma?

What Is Asthma?

Asthma is a chronic lung disease that inflames and narrows the airways. Asthma causes recurring periods of wheezing (a whistling sound when you breathe), chest tightness, shortness of breath, and coughing. The coughing often occurs at night or early in the morning.

Asthma affects people of all ages, but it most often starts during childhood. In the United States, more than 25 million people are known to have asthma. About 7 million of these people are children.

To understand asthma, it helps to know how the airways work. The airways are tubes that carry air into and out of your lungs. People who have asthma have inflamed airways. This makes them swollen and very sensitive. They tend to react strongly to certain inhaled substances.

When the airways react, the muscles around them tighten. This narrows the airways, causing less air to flow into the lungs. The swelling also can worsen, making the airways even narrower. Cells in the airways might make more mucus than usual. Mucus is a sticky, thick liquid that can further narrow the airways.

This chain reaction can result in asthma symptoms. Symptoms can happen each time the airways are inflamed.

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Sometimes asthma symptoms are mild and go away on their own or after minimal treatment with asthma medicine. Other times, symptoms continue to get worse. When symptoms get more intense and/or more symptoms occur, you're having an asthma attack. Asthma attacks also are called flareups or exacerbations.

Asthma Causes and Triggers

No one really knows what causes asthma. What we do know is that asthma is a chronic inflammatory disease of the airways. The causes of asthma symptoms can vary for different people. Still, one thing is consistent with asthma: when airways come into contact with an asthma trigger, the airways become inflamed, narrow, and fill with mucus.


Almost all asthma sufferers have allergies. In fact, over 25% of people who have hay fever (allergic rhinitis) also develop asthma. Allergic reactions triggered by antibodies in the blood often lead to the airway inflammation that is associated with asthma.

Common sources of indoor allergens include animal proteins (mostly cat and dog allergens), dust mites, cockroaches, and fungi. It is possible that the push towards energy-efficient homes has increased exposure to these causes of asthma.


Many people with asthma have aspirin-sensitive asthma and it's possible they're sensitive to other medications such as anti-inflammatory drugs like ibuprofen (Advil, Motrin), naproxen (Aleve, Naprosyn), aspirin, and beta-blockers (used to treat heart disease, high blood pressure, and glaucoma). If you know you're sensitive to these drugs, make sure your doctor has the problem documented on your chart, and always talk to your pharmacist about this reaction before taking a new medication.

Environmental Factors

Allergic reactions and asthma symptoms are often the result of indoor air pollution from mold or noxious fumes from household cleaners and paints. Other indoor environmental factors associated with asthma include nitrogen oxide from gas stoves. In fact, people who cook with gas are more likely to have symptoms such as wheezing, breathlessness, asthma attacks, and hay fever.

Pollution, sulfur dioxide, nitrogen oxide, ozone, cold temperatures, and high humidity have all been shown to trigger asthma in some individuals.

During periods of heavy air pollution, there tend to be increases in asthma symptoms and hospital admissions. Smoggy conditions release the destructive ingredient known as ozone, causing coughing, shortness of breath, and even chest pain. These same conditions emit sulfur dioxide, which also results in asthma attacks by constricting airways.

Weather changes have also been known to stimulate asthma attacks. Cold air can lead to airway congestion, bronchoconstriction (airways constriction), secretions, and decreased mucociliary clearance (another type of airway inefficiency). In some populations, humidity causes breathing difficulties as well.


Overweight adults - those with a body mass index (BMI) between 25 and 30 - are 38% more likely to have asthma compared to adults who are not overweight. Obese adults - those with a BMI of 30 or greater - have twice the risk of asthma. According to some researchers, the risk may be greater for non-allergic asthma than allergic asthma.

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The way you enter the world seems to impact your susceptibility to asthma. Babies born by Caesarean sections have a 20% increase in asthma prevalence compared to babies born by vaginal birth. It is possible that immune system-modifying infections from bacterial exposure during Cesarean sections are responsible for this difference.

When mothers smoke during pregnancy, their children have lower pulmonary function. This may pose additional asthma risks. Research has also shown that premature birth is a risk factor for developing asthma.


People who undergo stress have higher asthma rates. Part of this may be explained by increases in asthma-related behaviors such as smoking that are encouraged by stress. However, recent research has suggested that the immune system is modified by stress as well.


Strenuous exercise can cause a narrowing of the airways in about 80% of people with asthma. In some people, exercise is the main trigger for their asthma symptoms. If you have exercise-induced asthma, you will feel chest tightness, coughing, and difficulty breathing within the first five to eight minutes of an aerobic workout. These symptoms usually subside in the next 20 to 30 minutes of exercise, but up to 50% of those with exercise-induced asthma may have another asthma attack six to 10 hours later. It is important to warm up slowly and adequately prior to rigorous exercise. This may prevent an attack.

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It is possible that some 100 genes are linked to asthma - 25 of which have been associated with separate populations as of 2005.

Genes linked to asthma also play roles in managing the immune system and inflammation. There have not, however, been consistent results from genetic studies across populations - so further investigations are required to figure out the complex interactions that cause asthma.

Mom and Dad may be partially to blame for asthma, since three-fifths of all asthma cases are hereditary. The Centers for Disease Control (USA) say that having a parent with asthma increases a person's risk by three to six times.

Genetics may also be interacting with environmental factors. For example, exposure to the bacterial product endotoxin and having the genetic trait CD14 (single nucleotide polymorphism (SNP) C-159T) have remained a well-replicated example of a gene-environment interaction that is associated with asthma.

Sinusitis and Other Upper Respiratory Infections

Much like asthma causes inflammation in the lining of the airways, sinusitis causes inflammation in the mucous membranes that line the sinuses. This inflammation causes the mucous membranes in the sinuses to secrete more mucus -- also similar to asthma. When the sinuses get inflamed, the airways respond similarly in many people with asthma, leading to sinusitis with asthma. Prevention and prompt treatment of a sinus infection is often necessary to help relieve asthma symptoms.

Airway Hyperreactivity

Researchers are not sure why airway hyperreactivity is another risk factor for asthma, but allergens or cold air may trigger hyperreactive airways to become inflamed. Some people do not develop asthma from airway hyperreactivity, but hyperreactivity still appears to increase the risk of asthma.


Atopy - such as eczema (atopic dermatitis), allergic rhinitis (hay fever), allergic conjunctivitis (an eye condition) - is a general class of allergic hypersensitivity that affects different parts of the body that do not come in contact with allergens. Atopy is a risk factor for developing asthma.

Some 40% to 50% of children with atopic dermatitis also develop asthma, and it is probable that children with atopic dermatitis have more severe and persistent asthma as adults.

Smoking as Risk Factor for Asthma

The well-established approach to the connection between tobacco smoking and asthma is very conservative. Smoking (first-hand or second-hand) is a substantial risk factor for asthma development. Most public resources support this point of view: that smoke from cigars, cigarettes, and pipes is a powerful trigger for asthma symptoms.

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The mechanism of action is defined as following. When a person inhales tobacco smoke, irritating substances settle in the moist lining of the airways. These substances can cause an attack in a person who has asthma. In addition, tobacco smoke damages tiny hair-like structures in the airways called cilia. Normally, cilia sweep dust and mucus out of the airways. Tobacco smoke damages cilia so they are unable to work, allowing dust and mucus to accumulate in the airways. Smoke also causes the lungs to make more mucus than normal. As a result, even more mucus can build up in the airways, triggering an attack.

As to the second-hand smoking, adults and children who live with a smoker are more likely to develop respiratory illnesses. Children are especially at risk because their lungs are smaller and still developing. Exposure to second-hand smoke can lead to decreased lung function and symptoms of airway inflammation such as cough, wheeze, and increased mucus production, especially in children. Children with asthma are especially sensitive to second-hand smoke. They are more likely to develop asthma symptoms when exposed to second-hand smoke. They are also more likely to develop lung and sinus infections. These infections can make asthma symptoms worse and more difficult to control.

The problem is that the results of the related studies are surprisingly mixed, offering a strong positive correlation of up to 30% asthma development risk increase for smokers in one study and substantial negative correlation results in another. For example, one study in Finland revealed the fact that asthma risk increased with number of cigarettes smoked per day up to 14 but was significantly lower in those who smoked 15 or more cigarettes per day. The same trend held true for cigarette years, with asthma risk being higher in the 1-to-199 cigarette years category, and lower in the over 200 category. Another interesting discovery was that for ex-smokers the risk to develop asthma is higher than for active smokers.

Here are some other results obtained from the studies:

  1. From the National Jewish Medical and Research Center comes a 2012 report that the heavier pollution during the winter months does not worsen asthma.  A three year study focusing on minority children in urban areas found that respiratory infections, such as colds, rather than particulate matter, such as found in secondhand smoke, is responsible for triggering asthma attacks.  The press release ends with some common sense advice for parents to not worry about air pollution but pay closer attention to "preventing and treating the real wintertime threat to their children's health - colds and other respiratory infections."
  2. Based on Government Environment Protection Agency (EPA) report, the number of children whose blood levels showed effects from second hand smoke declined by about one-fifth to one-half between 1988 and 2000, depending on their levels of exposure. Those figures are obtained by tracking the amount of cotinine, a breakdown product of nicotine in blood. But the report also found that the percentage of children getting asthma has doubled in two decades, rising from 3.6 percent in 1980 to 8.7 percent, or 6.3 million children by 2001. These results distortion is not in EPA interests, since this organization was trying to reach an opposite conclusion. It is obvious that there are other risk factors for asthma development, much stronger than tobacco smoking.
  3. There is one more research, performed in California, which showed the similar trends. The percentage of Californians who have been diagnosed with asthma at some point in their lives is significantly higher than the national average, while California has the second lowest rate of smoking in the nation. The San Francisco Bay Area, the most health obsessed region in the state has higher rates of asthma than the rest of the state. One of the researchers suggested that the asthma cases are indeed triggered by environment, but with a completely negative connotation.  "Our clean living ways perhaps might be leading to this global rise in asthma and allergies. Most people assume asthma results from air pollution or other dirt in the environment. But it may be caused by just the opposite. The latest research shows the cleaner the environment, the more cases of asthma. It has to do with our immune systems”.

There have been other studies that suggest that our hyper-consciousness of "health" and our attempt to raise children in an antiseptic environment contribute to weak immune systems.  May be, it is time to reverse our cleanness-conscious attitude, and make a step back to the Mother Nature?

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