What is bronchial asthma?
Bronchial asthma, also called bronchial asthma or just asthma, is a chronic inflammation of the bronchial tubes and the resulting hypersensitivity of these. As a widely branched system of tubes, the so-called bronchi conduct the human respiratory air from the trachea to the alveoli (i.e. pulmonary alveoli), where the gas exchange, i.e. the absorption of oxygen into the blood and the release of carbon dioxide into the exhaled air, also takes place. The mucous membrane inside the bronchial tubes swells and develops a viscous mucous fluid. This causes the inner diameter of the bronchial tubes to narrow, making it difficult for the affected person to breathe in and out. Consequently, the breathing rate is increased and the person breathes faster. If the case is severe, it can lead to hyperinflation, in which the exchange of gases is limited and a lack of oxygen in the human blood can develop. Since asthma occurs in episodes, the symptoms can always improve in between. In general, there are two types of asthma: allergic asthma is usually triggered by pollen, dust or food. Non-allergic asthma is triggered by physical exertion, cold, tobacco smoke or stress.
Bronchial asthma is an inflammatory disease - the omega-3 fatty acids eicosapentaenoic acid (EPA for short) and docosahexaenoic acid (DHA for short) investigated in the study are thought to have an inflammatory effect: DHA) are thought to have anti-inflammatory effects, which is why their causality with chronic airway inflammation has now been explored.
Two important fatty acids:
EPA and DHA are fatty acids composed of a carbon chain, oxygen and hydrogen atoms. In addition to EPA and DHA, there is also alpha-linolenic acid, which the human body can convert into eicosapentaenoic acid, docosahexaenoic acid and docosapentaenoic acid. Omega-3 fatty acids serve the body, among other things, as components of cell membranes (i.e. for flexibility and permeability) and as a starting substance for the formation of tissue hormones (i.e. effect on blood pressure, immune defence and inflammation). In addition, the human brain is also largely composed of fat, with DHA as the most important fatty acid component of the cerebrum (i.e. brain). With the help of a specific enzyme - delta-6 desaturase - the body can produce EPA and EHA with enzymes from plant-derived omega-3 fatty acids. There is a common variant (i.e. rs1535) in the gene of this enzyme that reduces enzyme activity. Consequently, people with this gene variant rely on dietary intake of DHA and EPA.
Cohort study in London:
The study, published in January 2021, in the journal European Respiratory Journal, used data from a large UK birth cohort (i.e. Children of the 90s) that recruited mothers who were pregnant in the early 1990s and have been studying their offspring since. The study, led by Queen Mary Univesity of London, analyzed the association between intake of EPA and DHA from fish in children at age 7 and the incidence of new cases of asthma with clinical diagnosis at ages 11 to 14.
According to the British Birth Cohort Children of the 90s, about 44.5% (2025 of 4542 children) of participants had the rs1535 gene variant (i.e., body can produce less EPA and DHA by itself). According to study research, it was researched that these same children were more likely to have asthma between the ages of 11 and 14 when parents recorded in the dietary questionnaire at baseline at age 7 that their children were less likely to eat fish.
Is there a link?
For the top quarter of children with the highest dietary intake of EPA and DHA, it was found that this higher fatty acid content was associated with a lower risk of asthma, as the risk was 51% lower compared to the lowest cohort quarter of omega-3 intake.
No link was found for children without the rs1535 gene variant (i.e. body can produce more EPA and DHA itself). Consequently, this study suggests a possible significant cause of bronchial asthma in children. Although the researchers were able to corroborate the findings on another cohort (Swedish BAMSE study), a clear causality has not yet been proven by this observational study.
Therefore, omega-3 fatty acid intake from fish was not directly associated with asthma in the cohort. Since gene variation can be detected by simple blood tests, randomized trials with placebo are possible - children at increased risk of developing asthma would thereby be treated with either fish oil capsules or placebo. If the incidence of asthma were to decrease, this therapy could potentially show a direct association.