Immune Responses, Asthma & The Diet, by Dr Nina Bailey


Asthma, characterised by wheezing, coughing, tight chest and shortness of breath, is a common chronic inflammatory disease affecting the airways.  One in every five households in the UK will contain at least one asthma sufferer, with around 5.4 million people (of which 1.1 million are children) currently receiving treatment for the condition.

When a person with asthma comes into contact with something that irritates their airways, the muscles around the walls of the airways tighten and the airways narrow. This causes the lining to become inflamed, leading to swelling, which then causes difficulty in normal breathing.  The build-up of mucus, which is common in an attack, narrows the airway further, making it even more difficult to breathe.  If the attack is extreme and left untreated, the condition can be fatal.  For someone who suffers from asthma, the symptoms of airflow obstruction and bronchospasm can cause intense distress, and can have a profound effect on quality of life.  Many sufferers rely on inhaled corticosteroids, which act immediately to reduce the inflammation and allow normal breathing.

Sufferers are also often prescribed anti-leukotriene agents to control their asthma, since leukotrienes play a key role in an asthma attack (Hallstrand et al, 2010).  The primary function of these chemical substances, released by the many different cells of our immune system, is to help the body fight against infection.  In the case of asthma, the causes of a response can include: pollen, household cleaners and pets, all which can set off an allergic reaction in which the immune system goes into overload.  Leukotrienes exert their biological activities by binding to specific receptors and many pharmaceutical treatments for these conditions focus on blocking their actions at these receptor sites, therefore blocking the response.

Leukotrienes are complex molecules belonging to a larger family of hormone-like substances termed eicosanoids, of which some are inflammatory, setting the body in motion to fight against infection. Others are anti-inflammatory, with these released at the end of the response in order to send messages telling the body when the process is complete, and thus decrease the inflammatory process.  The over-production of inflammatory products, combined with the insufficient production of anti-inflammatory products can, however, have detrimental effects on the body.  Leukotriene B4 or LB4 is one such example of a highly inflammatory product produced by a specific omega-6 fatty acid called arachidonic acid (AA).  The products of AA are known to be involved in the development of several inflammatory diseases including asthma.

Given that different types of fat give rise to different end products, it is possible to manipulate the production of inflammatory or anti-inflammatory products simply by modifying our dietary intake of fat.  This is because the fat that we consume is incorporated into our cell membranes and therefore we really are, to some extent, what we eat.  Certain fats are released from our membranes at specific times and are converted to biologically active components. It is the long-chain omega-3 and omega-6 fats within our cell membranes that ultimately control the inflammatory process.

Consuming too much saturated fat and trans fat, both of which are associated with heavily processed foods and junk foods, takes up vital space within our cell membranes.  Combining this with a high intake of omega-6, as found in many plant oils and red meat, with a low intake of omega-3, found in fish and shellfish, will increase the risk of unhampered inflammation.   Indeed, an increased intake of omega-6, and especially low intakes of omega-3, is suggested to play a causal role in the increasing incidence of asthma (Galli & Calder 2009).  It has also been suggested that supplementation with fish oil during pregnancy may reduce sensitisation to common food allergens and reduce the prevalence and incidence of asthma, as well as eczema and  hay fever.

Encouragingly, omega-3 supplementation is being investigated as a viable non-pharmaceutical method to decrease the severity of asthma attacks in sufferers.  Dietary supplementation with omega-3 fatty acids on their own, or combined with zinc and vitamin C, have been shown to significantly improve asthma control tests, pulmonary function tests and pulmonary inflammatory markers in children with moderately persistent bronchial asthma (Biltagi et al, 2009; Schubert et al, 2009).

Environmental pollutants have often been blamed for the increase in asthma prevalence witnessed over the last few decades, and whilst there may indeed be some truth to this, significant changes in dietary eating patterns have also taken place in the last few decades, which may have a greater role in asthma prevalence than previously thought. Indeed, high intake of omega-6 and low intake of omega-3 is known to enhance inflammation and simply by correcting the balance of omega-6 to omega-3, this can bring significant improvements where inflammation is predominant. The role of high strength omega-3 supplements in inflammatory conditions is certainly emerging as a viable treatment, not only for asthma sufferers but also for many other conditions in which there is chronic inflammation.

References

Biltagi MA, Baset AA, Bassiouny M, Kasrawi MA, Attia M. Omega-3 fatty acids, vitamin C and Zn supplementation in asthmatic children: a randomized self-controlled study. Acta Paediatr. 2009 98:737-42.

Galli C, Calder PC. Effects of fat and fatty acid intake on inflammatory and immune responses: a critical review. Ann Nutr Metab. 2009 55:123-39.

Hallstrand TS, Henderson WR Jr. An update on the role of leukotrienes in asthma. Curr Opin Allergy Clin Immunol. 2010 10:60-6. Review.

Schubert R, Kitz R, Beermann C, Rose MA, Lieb A, Sommerer PC, Moskovits J, Alberternst H, Böhles HJ, Schulze J, Zielen S. Effect of n-3 polyunsaturated fatty acids in asthma after low-dose allergen challenge. Int Arch Allergy Immunol. 2009 148:321-9.

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