Asthma affects as many as 334 million people of all ages in all parts of the world.(1) This number continues to increase rapidly, and researchers believe this is due to a number of factors including increased air pollution and allergens, as well as obesity and dietary habits. In the UK, there are 5.4 million people with asthma (1.1 million children and 4.3 million adults), which means that asthma affects one in every 11 people.
It is reported that every ten seconds someone in the UK is having a potentially life-threatening asthma attack.(2) In the US, the number of adults who currently have asthma is 17.7 million and the number of children is 6.3 million.(3)
Asthma is a chronic inflammatory disease of the airways of the lungs and it is one of the most common chronic inflammatory disorders. It is characterised by recurrent attacks of breathlessness and wheezing, which vary in severity and frequency from person to person. Symptoms may occur several times in a day or perhaps several times per week in affected individuals. The triggers of asthma also vary and can include physical exercise, cold weather, hot weather, pollen, pollution or physical exercise. We don’t know what causes asthma and there is currently no known cure for asthma but most people with asthma who receive the right treatment find they can control their symptoms and lead normal lives. he most overwhelming symptom for most people that suffer from asthma is difficulty breathing, but it is not the only one. Asthma is often accompanied by a sensation of tightness in the chest, making you feel as if your chest is being squeezed, somewhat like a wide rubber band stretched tightly around the chest. Wheezing is also a symptom of asthma and coughing is also common which can become worse at night.
My youngest son has asthma and I see the effects of this chronic condition first hand. I remember when my son came downstairs one morning and he was having a real hard time breathing due to an asthma attack. This was a very scary situation as you can probably imagine. Sometimes, we underestimate how serious asthma is because it is generally controlled by mediation and inhalers. However, it is at times like this that we get a chilling reminder of just what this condition can do. To get a better understanding of asthma and its impact on health, we need to learn a little bit about how the lungs work. Let’s take a closer look.
How the Lungs Work
When you breathe in, you take in air. The lungs extract the oxygen from the air that is vital for every cell in our body. The oxygen is then passed into the blood and circulated around the body. Carbon dioxide is the waste product of this exchange and this is what we breathe out.
Figure 1.1 The lungs and the bronchial tree
Lets go into more detail on this amazing process that gives us the oxygen for life. In figure 1.1 above, we can see that when we take a breath the air travels down the windpipe (trachea). The trachea then branches into two sections, each one called a bronchus. The right bronchus goes to the right lung and the left bronchus goes to the left lung. Each bronchus then branches out into more bronchi (the plural for bronchus) and then these bronchi, in turn, branch out into smaller tubes called bronchioles. This trachea, bronchi and bronchiole structure is known as the bronchial tree, with the trachea as the trunk of the tree. The final branches, or the last bronchioles in the bronchial tree, are called the respiratory bronchioles, and these divide onto tiny openings called alveolar ducts. These microscopic tubes open into the alveoli, which is the plural for alveolus. There can be several alveoli coming off one duct so that they are clumped together.
It is in the alveoli that one of the most important processes that sustains all of life takes place – the gas exchange of oxygen and carbon dioxide. Oxygen is transported into the bloodstream by diffusing through the walls of the alveoli and into the capillaries. From here, the oxygen is carried around the body by a protein called haemoglobin in the red blood cells. This freshly oxygenated blood is carried from the lungs to the left side of the heart and pumped around the body. Once the oxygen has been used, the blood – now carrying waste products such as carbon dioxide – is carried back to the right side of the heart in the veins, where the waste products are then pumped into the lungs. The lungs will then remove the carbon dioxide through the alveoli, so that we can breathe out the carbon dioxide. Now that we know a little bit more about how the lungs work, we can move on to take a closer look at asthma.
Common Asthma Triggers
An asthma trigger is anything that can set off your asthma by irritating your sensitive airways. There are many asthma triggers and what sets off one person’s asthma symptoms can be different from someone else’s. For example, a high pollen count can trigger asthma symptoms in one person whereas cold weather will be a trigger in another person.
A person with asthma can have more than one trigger and at the same time. When this happens, there can be a stronger reaction and the asthma symptoms can be worse. Sometimes, a known asthma trigger won’t have much of an effect and this is because the sensitivity of the airways can vary on a day-to-day basis. If you have asthma, it is important to understand your triggers. In my son’s case, we know what that high pollen counts and freshly cut grass are particularly potent triggers; however, being around our lovable pet cat, who he adores, has no effect at all. The list below shows the most common asthma triggers.
Sometimes, a bit of detective work is required to identify what the triggers are, and it is a good idea to keep a diary of activities and symptoms if you suffer with asthma. This will help you identify any patterns and take action accordingly.
What Happens in Asthma?
Take, for example, a summer’s day and the pollen count is high. You may be out in the garden mowing the lawn – this is an irritant that can trigger asthma. The airways become inflamed and the muscles around the airways start to tighten up so that the airways become narrower. This is called bronchoconstriction. There can also be a build-up of mucus and the already narrowed airways become congested, making it harder to get air in and out of the lungs. Essentially, asthma is an immune response in the bronchial airways that is triggered by certain stimuli. In figure 1.2 below we can see the difference between a normal airway and the constricted, narrower airway of a person with asthma.
Figure 1.2 Normal airways and airways of a person with asthma
Asthma that is triggered by an allergen is known as allergic asthma, and this is the most understood of the factors that cause asthma. An estimated 80% of asthma patients have an allergy of some kind and, as mentioned previously, allergies have been increasing in recent years. Researchers are not entirely sure on the reasons for this rise, but it is thought that air pollution, antibiotics and dietary habits could be part of the reason. Studies show that children who grow up on farms – where they are exposed to more pollen, grass, dirt and bacteria – actually have fewer allergies than children growing up in cities.(4)
Essentially, a person with asthma has a susceptibility to environmental influences, such as allergens, and this can be made worse by exposure to a viral infection. This culminates in an inappropriate inflammatory response to allergens that are normally harmless. Activated T-cells have the capacity to control the amount and nature of inflammatory responses and research has shown that asthma patients have an increased level of Th2 cells or what is called Th2 dominance.
The Inflammatory Response in the Airways
The inflammatory response in the airways involves a complex interplay of the respiratory tract or epithelium, the innate immune system and the adaptive immune system. Chronic inflammation in asthma usually includes an increase in the number of activated Th2 cells. These cells produce the inflammatory cytokines which are responsible for IgE (immunoglobulin E) antibody production. White blood cells called eosinophils are released into the circulation and these are a rich source of leukotrienes, which contract the smooth muscle in the airways. It is these leukotrienes that are primarily responsible for the bronchoconstriction in asthma.
So now we have a number of reactions going on here in response to a stimulus such as an inhaled allergen. We have structural changes happening in the lungs as the walls of the airways become inflamed, we have increased mucus production by goblet cells and we have immune cells being activated to seek and destroy the foreign invaders. In addition, we have a number of ‘transcription factors’ involved in asthmatic inflammation. Transcription factors are proteins involved in the process of converting, or transcribing, DNA into RNA. As we know, DNA is the molecule that contains our genetic code – all of the information needed for our cells to do their jobs throughout our lives. However, these genes need to be copied through a process called ‘transcription’. The copy is called mRNA and it is this copy that is then turned into a gene product. However, not every gene needs to be expressed (or ‘switched on’) at the same time or in the same amount, and so gene expression needs to be controlled. This is the role of transcription factors. In asthma, these transcription factors act on genes to initiate the inflammatory cytokines and mediators that induce and perpetuate the inflammation involved in asthma.
Several years ago, it was discovered that a degree of inflammation is present in the bronchial tubes of people with asthma, even when they are feeling well with no symptoms. Now this inflammation may be so mild as to go unnoticed most of the time; however, this persistent and low-level inflammation makes the bronchial tubes more susceptible. The bronchial tubes are said to be ‘twitchy’ and more vulnerable to being triggered by stimuli such as allergens or the cold, for example. While the cause of asthma is not fully understood and a huge amount of research is going on in this area, chronic inflammation is thought to be a key factor in making the bronchial tubes twitchy.
Current Treatments for Asthma
Corticosteroids, which are often the treatments prescribed to manage asthma, modulate immune inflammatory responses in asthma by inhibiting the transcription factors listed above. In conjunction with corticosteroids, beta2-agonists are also used as effective bronchodilators.
These bronchodilators make breathing easier by relaxing the muscles in the lungs and widening the airways or bronchi. There are two types of bronchodilators called ‘short acting’ and ‘long acting’. The short acting bronchodilators are also known as relievers or rescue medication, and are used for acute asthma symptoms or sudden asthma attacks to open up the airways. The long acting bronchodilators are used to control longer term asthma symptoms, to reduce the ‘twitchiness’ of the bronchial tubes and make them less vulnerable to an inflammatory response that narrows the airways and produces mucus. That is why a person with asthma will take these medications every day, even when they feel well. Essentially, bronchial dilators control the systemic, low level inflammation that is present in the bronchial tubes.
It is not known how we can turn off this low level inflammation in the bronchial tubes, but there are a number of ways to reduce it. One method, of course, is through the long acting bronchodilator medication explained above. The other primary method is to avoid or reduce the exposure to triggers such as allergens, pollution, dust, pet dander and cold. However, that is easier said than done in today’s world where we are exposed to a myriad of pollutants and allergens every day. However, awareness is the first step to being able to make more informed decisions.
Can Food Have an Impact on Asthma?
Certainly, there are foods that are known to make asthma symptoms worse, such as shellfish, cow’s milk, eggs, yeast products and nuts. Just how much of an impact these foods have will vary from person to person; therefore, if you have asthma, it is important to monitor how these foods affect you.
By the same token, there are foods that can help to reduce the severity of asthma symptoms and improve lung function. Research shows that eating a diet rich in fruit and vegetables can help, which is really no surprise. Researchers hypothesised that the change in diet with westernisation may be responsible for the increase in asthma prevalence. Observations have shown that the consumption of foods rich in anti-oxidants (vitamin C, vitamin E, carotenoids, flavonoids, selenium and zinc) has decreased in countries such as the UK, while asthma prevalence has increased. Research has shown that diets rich in vitamin C, beta-carotene, magnesium and selenium are associated with a reduction in asthma prevalence and can potentially prevent or at least limit the inflammatory response in the airways.(5) In one study, adolescents with the lowest dietary intakes of anti-oxidant and anti-inflammatory micro-nutrients had lower lung function and increased respiratory symptoms, suggesting that adequate dietary intake may promote respiratory health and lessen the effects of oxidative stress.(6) In another study, researchers found symptomatic asthma in adults to be associated with a low intake of the dietary anti-oxidants vitamin C and manganese. The low intake of vitamin C appears to be primarily associated with a diet deficient in fruit.(7)
Recent epidemiological studies reported that a low incidence of asthma was significantly observed in a population with a high intake of flavonoids. Flavonoids possess anti-allergic activities that inhibit histamine and interleukin-4 and fruit and vegetables are high in flavonoids.(8)
Other dietary studies included a study of 598 Dutch school children ranging from 8 to 13 years old, which found that the risk of asthma was lessened by 54% in those that consumed wholegrains frequently and by 66% in those who consumed fish frequently.(9) In addition, diets high in the omega 6 fatty acids found in vegetable oils, margarines and farm raised meats has been associated with the increasing number of people with asthma. This increase in consumption of omega 6 fatty acids has coincided with a decrease in the consumption of saturated fats. There is also evidence showing a decrease in the consumption of oily fish, which contains omega 3.(10) This situation has led to the huge imbalance of omega 6 and omega 3 fatty acids, which is contributes to many inflammatory conditions.
Research has shown that adherence to the Mediterranean diet has a very beneficial effect on asthma and other allergies such as rhinitis. It was observed that for children in Crete, Greece, asthma and rhinitis were very rare and a study was conducted to see if this was attributed to the Mediterranean diet. They found that 80% of children ate fresh fruit at least twice a day and 68% ate vegetables twice a day.
These included grapes, oranges, apples and fresh tomatoes because these are the main local products in Crete. The results of the study showed that these foods were protective for wheezing and rhinitis. A high consumption of nuts was also found to be inversely associated with wheezing, whereas margarine increased the risk of both wheeze and allergic rhinitis. In conclusion, the results suggest that adherence to the Mediterranean diet, with fruits and vegetables eaten every day, had a beneficial effect on the symptoms of asthma and allergic rhinitis, and explains the relative lack of allergic symptoms in this population.(11)
Asthma is a complex disease that has many contributing factors including genetics, dietary habits, environmental toxins and lifestyle. It is clear to see from the research above that diet plays an important role in the development of asthma and also in reducing the symptoms of asthma. A healthy diet that is rich in fruit, vegetables, wholegrains and oily fish has been shown to reduce the symptoms of asthma and improve lung function. This is certainly food for thought, not just for those suffering from asthma but for everyone looking for healthier dietary habits. Are you getting your 5 a day?
For more information on asthma:
1. Global Asthma Network. The Global Asthma Report 2014. Vol 5.; 2014. doi:ISBN: 978-0-473-29125-9\r978-0-473-29126-6.
2.Asthma UK. Asthma UK | Asthma facts and statistics. https://www.asthma.org.uk/about/media/facts-and-statistics/.
3. CDC. FastStats - Asthma. https://www.cdc.gov/nchs/fastats/asthma.htm.
4. Sciences HH, Miller ME, Byington RP, et al. Exposure to Environmental Microorganisms and Childhood Asthma. N Engl J Med. 2011:2545-2559. doi:10.1056/NEJMoa1402685.
5. Kim J-H, Ellwood PE, Asher MI. Diet and asthma: looking back, moving forward. Respir Res. 2009;10:49. doi:10.1186/1465-9921-10-49.
6. Burns JS, Dockery DW, Neas LM, et al. Low dietary nutrient intakes and respiratory health in adolescents. Chest. 2007;132(1):238-245. doi:10.1378/chest.07-0038.
7. Patel BD, Welch AA, Bingham SA, et al. Dietary antioxidants and asthma in adults. Thorax. 2006;61(5):388-393. doi:10.1136/thx.2004.024935.
8. Kawai M, Hirano T, Higa S, et al. Flavonoids and related compounds as anti-allergic substances. Allergol Int. 2007;56(2):113-123. doi:10.2332/allergolint.R-06-135.
9. Tabak C, Wijga AH, De Meer G, Janssen NAH, Brunekreef B, Smit HA. Diet and asthma in Dutch school children (ISAAC-2) Topic collections Diet and asthma in Dutch school children (ISAAC-2). Thorax. 2006;61:1048-1053. doi:10.1136/thx.2005.043034.
10. Black PN, Sharpe S. Dietary fat and asthma: Is there a connection? Eur Respir J. 1997;10(1):6-12. doi:10.1183/09031936.97.10010006.
11. Chatzi L, Apostolaki G, Bibakis I, et al. Protective effect of fruits, vegetables and the Mediterranean diet on asthma and allergies among children in Crete. Thorax. 2007;62(8):677 LP-683. http://thorax.bmj.com/content/62/8/677.abstract.
Sports & fitness nutritionist, researcher and author on a mission to improve the human condition. Focusing on evidence-based and outcome-based nutrition, training, mindset & environment