Asthma is a chronic respiratory condition resulting in breathing difficulties caused by inflammation and narrowing of the major airways (the bronchi) in the lungs. Although asthma is a chronic illness, the process of inflammation and bronchial narrowing is usually reversible and this happens either naturally or aided by medications. Exacerbation of asthma symptoms usually requires an obvious trigger which irritates the smooth muscles of the bronchi causing them to constrict and produce more mucus which makes it hard to breath. During an acute worsening of symptoms a sufferer is said to be experiencing an asthma attack. The severity of the symptoms of asthma differs from person to person, from mild to severe.
Asthma is relatively common and is estimated to affect around 300 million people worldwide1. In the US alone asthma affects roughly 20 million, including 5-6 million children, and results in roughly 4000 deaths every year2, while in the UK 5 million people have asthma and over 1300 deaths per year are attributed to acute asthma attacks3.
The severity and duration of asthma symptoms vary from person to person and also in the same individual. The primary symptoms of asthma are:
- Shortness of Breath (gasping)
- Tightness in the Chest (like a heavy weight is pushing down on your chest)
- Coughing (more common in children)
- Wheezing (a whistling sound when breathing)
A severe asthma attack can often take a considerable amount of time to develop. It may take between 6 and as many as 48 hours before symptoms become serious.
This fact however allows asthma sufferers to look out for signs of an impending asthma attack and take measures to reduce the chances of it occuring, or at least be prepared to deal with it. Signs that should alert an asthma sufferer to the chance of an attack include:
- Increase Pulse Rate,
- Increase Wheezing
- Feeling Agitated or Restless.
- A Drop in Peak Expiratory Flow Rate*
*Peak Expiratory Flow Rate refers to the amount of air you are able to breathe out of your lungs. It can be measured with a hand-held device known as a peak flow meter which your doctor may give you to monitor your symptoms and triggers or you can purchase one privately.
Symptoms of an acute asthma attack commonly include:
- Rapid Worsening of Symptoms
- Breathing and Talking Become Difficult
- Racing Pulse
- Lips and/or Finger Nails May Turn Blue (due to lack of oxygen)
- Tightening of Skin Around the Chest and Neck
- Nostrils May Flare When Trying to Breathe
Asthma is usually diagnosed during a consultation with your doctor who will be listening for the symptoms described above and will want to know about your medical history and if you have a family history of allergic conditions in your family, since this increase the chances of you having asthma. Your doctor will also usually perfrom a chest examination and listen to your breathing with a stethoscope to see if he/she can hear any signs of asthma such as constricted airways, wheezing, and increased respiratory rate (the number of times you breathe in and out during a minute)
Your doctor will also be interested in the circumstances surrounding the onset of your symptoms (or those of your child), including when and where they occurred. Other important details the doctor needs to know is if any medicines are being taken, details about work/school and home environments, and occupation in adults. This information can be used to help identify possible triggers for the asthma.
A common problem surrounding diagnosis is that people with asthma can appear perfectly healthy unless they are experiencing an asthma attack. If the doctor is not sure of the diagnosis he may have you take a test such as the peak expiratory flow rate (PEFR) test, which was briefly described above. After an initial reading is taken at the doctor's surgery, you will usually be given a short course of a medicine known to be effective in treating asthma. On a return visit to the doctor a second reading is then taken. If your peak expiratory flow rate is significantly higher after taking the anti-asthma medicine, then the diagnosis of asthma is normally confirmed.
Asthma Causes & Triggers
There are a number of well known factors that can predispose an individual to develop asthma, either in childhood or later in life. The most common and important of these include:
- Family history of asthma, or other related allergic conditions (known as atopic conditions), including eczema/atopic dermatitis and hayfever.
- Having or developing another atopic condition yourself.
- Frequent respiratory infections.
- Being male
- Having bronchiolitis as a child (a common childhood lung infection).
- Being exposed to tobacco smoke as a child.
- Being born prematurely and/or with a low birth weight.
Research has shown increasing incidence of asthma in developed nations over the past few decades, including the USA4 and Europe5. The link between genetic predisposition and asthma is well established but cannot explain why asthma has become so much more common in a relatively short space of time. It is therefore likely that environmental and dietary factors are major contributors.
Asthma is a hypersensitivity of the airways to various triggers. Anything that can trigger the process of inflammation in the bronchi can trigger asthma. Some of the most important of these include:
Viral chest infections are a common cause of asthma since any infection of the airways causes immune activation and the inflammation which causes airway constriction and the symptoms of asthma. Bacteria, fungi, and parasites may also be responsible for causing respiratory infections and asthma in some people.
Certain drugs are well known triggers of asthma. The most common being the class of painkillers known as nonsteroidal anti-inflammatory drugs (NSAIDs), the most well-known of which are aspirin and ibuprofen. Also, a class of medications called beta-blockers, which are used in the treatment of high blood pressure, and sometimes for anxiety and panic attacks, can sometimes trigger symptoms of asthma.
Changes in weather conditions, particularly rapid changes or extreme conditions, are known to trigger asthma attacks. The trigger is often particularly cold or dry air.
Exercise is a factor that is well known for bringing on the symptoms of asthma. It is thought that the increased respiratory rate causes cooling and drying of the lining of the airways which in turn causes irritation and triggers asthma. Not all forms of exercise are likely to be problematic for all asthma sufferers so individuals need to be aware of their own triggers. Running outside in cold or polluted air for example is more likely to bring on an attack than swimming in a warm climate (unless chlorine is a problem).
A review of epidemiological and human challenge studies found that both ozone and particulate matter can exacerbate airway inflammation in asthmatics6. Ozone is a principal component of smog and at ground level is produced when nitrogen oxides (NOx) and volatile organic compounds (VOCs or hydrocarbons) from vehicle exhausts and industrial sources react. This process is increased by sunlight and warm temperatures. The US Environmental Protection Agency describes particulate matter as "...a complex mixture of extremely small particles and liquid droplets. Particle pollution is made up of a number of components, including acids (such as nitrates and sulfates), organic chemicals, metals, and soil or dust particles." Particulate matter is produced by natural processes such as forest fires but more importantly is produced when pollutants from industry and vehicle exhausts (particular diesel vehicles) react in the air. Although industrial processes and vehicles are becoming more efficient and less polluting the rapidly increasing number of power plants, factories, and vehicles, coupled with higher temperatures due to climate change, suggest asthma rates will only continue to climb.
A study carried out by the University of Sourthern California in 2006 found that children living within 75 metres of a major road were 50% more likely to have exhibited asthma symptoms in the past year than children who lived more than 300 metres away7. Higher traffic volumes were also related to increased rates of asthma. In another study in New York City found that that among children aged four and five, asthma rates fell by 25% for every extra 343 trees per square kilometre8. The suggestion being that trees absorb pollution making for cleaner air in areas with a higher density of trees (read more about trees, pollution and asthma).
Other forms of air pollution that can trigger asthma include cigarette smoke and fumes from household chemicals. Children living in households where there is heavy use of chemical products such as disinfectants, bleach, window cleaners, air fresheners, and pesticides, are 41% more likely to develop asthma by age 7 than children in households with the lowest use of these products9. Strong evidence also links frequent use of chlorinated swimming pools with an increased risk of childhood asthma10.
Since asthma is an atopic condition it shares many features in common with allergies and those who suffer from asthma are much more likely to suffer from other allergic conditions than otherwise healthy individuals. Those with asthma tend to have higher levels of immunoglobulin E (IgE) (the type of antibody associated with the allergic response) than those without, and the higher an asthma sufferer's IgE level, the more severe the asthma11.
Common airborne allergens associated with triggering asthma attacks include pollen (hayfever), dustmites, and pet/animal dander12, while a large European study found that sensitisation to moulds was linked to both incidence and severity of asthma13. Airborne allergens directly trigger an inflammatory response in the airways that can result in an asthma attack. First, IgE antibodies bind to the allergen and then this complex binds to cells known as mast cells which release histamine and other inflammatory chemicals, initiating the inflammatory response. In asthmatics this inflammatory response is more severe than in those without asthma and can result in excessive mucus production and closing of the airways, which in turn cause the symptoms of an asthma attack.
Although the connection may seem less obvious there is also a link between food allergies and asthma. More than a third of children who have food allergies also have asthma and up to 8% of asthmatic children have food allergies; food allergies are seen as a hidden trigger for asthma attacks which are often life-threatening14. Food allergens have been shown to trigger bronchospasm and asthma attacks but why this is the case is uncertain15. It is likely that food allergies trigger systemic inflammatory responses involving IgE and other immune mechanisms. What is known is that the development of food allergies early in life increases the risk for the development of inhalant allergies and respiratory symptoms later in life16. The most common food allergens are often referred to as the "big eight" and are fish, shellfish, milk, egg, soy, wheat, peanuts, and tree nuts such as walnuts, cashews.
Besides food allergies there are a number of other dietary factors that can increase the risk for asthma or trigger an attack.
A well known trigger of asthma in foods are sulphites (sulfites - US). Sulphites occur naturally in the body during the metabolism of sulphur-containing amino acids, are found naturally in many foods and beverages, and are common in fermented foods and beverages. Sulphites are also used as a food additive as a preservative. In asthmatics, consumption of sulphite-containing foods can trigger airway constriction. The mechanisms for this are not fully understood but Inhalation of sulphur dioxide (SO2) produced in the stomach following ingestion of sulphur-containing foods or beverages, a deficiency in a mitochondrial enzyme, and an IgE-mediated immune response have all been implicated17. To learn more about sulphite sensitivity and problematic foods see the article: Sulfites: Safe for Most, Dangerous for Some
The type of fats and oils consumed in the diet appear to be an important factor in asthma risk. During the 20th century there was a large increase in the amounts of Omega-6 fatty acids consumed due to widespread use of margarine, vegetable-based cooking oils, and their use in processed and packaged foods and meals. At the same time the consumption of Omega-3 fatty acids found in fish and certain plant foods remained the same or actually decreased. Scientists now know that the Omega-3:Omega-6 ratio in the diet is an important factor in disease development. Studies have shown that both higher blood concentrations of Omega-3 fatty acids and a higher Omega-3:Omega-6 ratio are protective against asthma18. The reasons for this are complex but simply speaking, Omega-3 fatty acids tend to produce anti-inflammatory chemicals in the body while Omega-6 fatty acids produce chemicals that are more likely to promote inflammation.
A low intake of antioxidants including vitamin C, selenium, manganese, and bioflavonoids in the diet through consumption of fruit and vegetables has also been linked to the development of asthma in both children19 and adults20,21. Antioxidants may afford a protective effect against asthma by neutralising free radicals from pollution and other sources and by modulating the inflammatory immune response.
The gastrointestinal tract is estimated to contain 100 trillion bacteria and other microorganisms which interact with the human host in a number of ways, particularly in terms of the immune system and immunity. Studies have shown the gut microflora plays a major role in the maturation of the immune system and the development of oral tolerance to foods, ensuring allergies do not develop; differences between the microflora of healthy and atopic infants have also been noted22. The use of antibiotics and the standard Western diet can both negatively impact the composition of the gut microflora and icrease the risk for asthma; these changes being found to influence the sensitivity of the airways23.