What is allergy?
An allergy is the inappropriate immune response to a normally harmless substance and for a sufferer it can be immensely distressing. An allergy can cause an array of symptoms; it may be anything from a runny nose and itchy eyes to an unpleasant skin rash and gastrointestinal symptoms that may include stomach ache and vomiting. The most severe allergies (known as anaphylaxis) can cause breathing problems or a drop in blood pressure that can be, in some cases, life-threatening.
Allergies first start when cells of the immune system wrongly identify a substance as an attacker and produce a class of antibodies known as IgE (immunoglobulin E). Specific to that particular allergen, IgE is then produced each time the allergen is encountered, alerting mast cells and basophils within the immune system to produce the histamine and proteins known as cytokines responsible for the allergic symptoms.
Are we too hygiene focused?
The cells of the immune system directly influence individual susceptibility to developing allergies. TH or T helper type white blood cells aid in fighting bacteria and viruses, and protect us against allergies. The cells known as Th2 cells can fight parasite infections, but make us more vulnerable to developing allergies. At birth, the immune system adapts to be either allergy prone (Th2) or non-allergy prone (Th1), depending on genetics (inherited) and environment; a reduced microbial exposure in early life is possibly responsible for a shift of the Th1/Th2 balance in the immune system towards the pro-allergenic Th2 response1.
It is generally accepted that when we are young the normal exposure to a variety of micro-organisms and bacteria enables the immune system to respond appropriately later in life. Unfortunately, we now live in an environment where we attempt to protect children from such contact through the use of cleaning products containing anti-microbial agents, and children are generally discouraged from getting ‘dirty’. Thus, this inadequate exposure to environmental micro-organisms could result in the immune system developing a tendency towards allergy, certainly in atopic Th2 children.
How many people suffer from an allergy?
Recent estimates from the Royal College of Physicians suggest that almost one-third of the total UK population – approximately 18 million people – will develop allergy at some time in their lives and that asthma, hay fever and eczema have increased in incidence two- to three-fold in the last 20 years2.
Common causes of allergy symptoms include:
- Food allergies, such as peanut, soy, wheat and dairy allergy
- Seasonal allergies such as hay fever resulting from grass, tree pollen or various moulds.
- Pet allergies, or allergies to house dust mites can also cause miserable symptoms such as itchy eyes, sneezing, nasal congestion and wheezing, while allergic skin conditions can cause a rash and itchy skin.
Can we influence our risk of developing an allergy?
One possible explanation for the observed increase in the incidence of allergic diseases over the last 20-40 years centres on the change in the typical Western diet from a relative balance between anti-inflammatory omega-3 fatty acids and pro-inflammatory omega-6 fatty acids, to a diet in which omega-6 fatty acids are overwhelmingly predominant. As the omega-6 family favour a Th2 differentiation of the immune system, the importance of dietary intake of omega-3 and omega-6 during pregnancy and infant development becomes significant: because high intake of omega-3 can displace the activity of pro-inflammatory omega-6 and lead to the more desirable production of anti-inflammatory products of the immune system, it has been hypothesised that supplementation during pregnancy and lactation may not only be beneficial to normal growth and development but also serve as a method of primary prevention of allergic diseases in childhood by shuttling the immune system to develop along a more balanced Th1/Th2 status3.
Is it safe to eat seafood during pregnancy?
When choosing oily fish, it is important to bear in mind that they can contain some environmental pollutants, such as methylmercury, PCBs (polychlorinated biphenyls) and dioxins. The general consensus is that the benefits of consuming fish outweigh the risks; pregnant women, however, are advised to consume no more than two portions a week and avoid larger longer-living fish species such as marlin and swordfish. Oily fish such as salmon, mackerel, sardines and anchovies are particularly rich in omega 3 fatty acids, as well as important protein and other vitamins and nutrients which are not only good for mum but also good for the developing baby. For those mothers with concerns over environmental pollutants, it is worth considering the use of highly purified and concentrated omega-3 supplements which can provide a convenient alternative to fish consumption.
- Ngoc, P.L., Gold, D.R., Tzianabos, A.O., Weiss, S.T. & Celedon, J.C. Cytokines, allergy, and asthma. Current opinion in allergy and clinical immunology 5, 161-6 (2005).
- Klemens, C.M., Berman, D.R. & Mozurkewich, E.L. The effect of perinatal omega-3 fatty acid supplementation on inflammatory markers and allergic diseases: a systematic review. BJOG: an international journal of obstetrics and gynaecology 118, 916-25 (2011).