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Asthma and allergy in Norway
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- Asthma and allergies are a frequent cause of ailments in children and adolescents in industrialised countries.
- More boys than girls have asthma and allergies before puberty.
- We know little about the causes of asthma and allergy.
- There are currently no known interventions to prevent the development of asthma and allergies among those who are healthy.
- Respiratory infections, allergens and environmental factors such as cigarette smoke, particulate matter and exhaust fumes, as well as chemicals from consumer products, may worsen symptoms in those who are already sick.
About asthma and allergies
Asthma is a chronic inflammatory condition or irritation of the respiratory tract that can be triggered by various factors (e.g. allergens, respiratory infections, exercise and air pollution). This can cause symptoms such as repeated coughing bouts, chest tightness, wheezing or rattling, especially at night or early morning. Between episodes, breathing can be normal. There are different types of asthma, including allergic and non-allergic, exercise-induced or occupational asthma.
Allergy is caused by an overreaction of the immune system following contact with various proteins, metals or chemicals. There are many types of allergies, and the most common are hay fever (rhinitis), atopic eczema, allergic contact dermatitis and food allergies.
The symptoms of hay fever are nasal discharge and itching nose and eyes. Impaired concentration, fatigue and lethargy may also occur. Most people with hay fever react to allergens in house dust, pets and pollen, as well as mould spores if there is high humidity.
Atopic eczema (often called infantile eczema) is a disease with itchy rashes that are typical in early childhood. Most of the children with atopic eczema grow out of their eczema before the teens. The trigger causes are unclear but children with allergic and asthmatic parents have an increased risk of developing atopic eczema.
Allergic contact dermatitis and hives
Allergic contact dermatitis often appears as a red and itchy rash that appears a few hours after contact with an allergen. In some cases, contact dermatitis only appears after the skin has been exposed to sunlight. This is called photo allergy. Hives (urticaria) occur rapidly after exposure and are characterised by localised swelling, redness and itchy skin sensations after direct contact with an allergenic substance. The most common contact allergen in children and adults is nickel, but several preservatives and fragrances also cause reactions. Proteins in food may also cause allergic skin reactions.
Food allergy is an immunological reaction that is limited to reactions to food that can be detected by specific IgE antibodies in blood samples (serum). Food allergies are caused by proteins in food, and usually trigger rapid reactions. It is common for symptoms to appear in other organs than the gastrointestinal system, such as the skin, respiratory and cardiovascular system.
The most common severe reactions in children are to egg, hazelnut, peanut and milk. Most children grow out of egg and milk allergies before school age. Nut allergy, and particularly peanut allergy, often last throughout life. In adults, reactions to hazelnut, peanut and wheat are most common, whereas reactions to fish are rarely reported.
Prevalence of asthma and allergy
There are no nationwide studies of the number of people with asthma and allergies in Norway, only studies that cover smaller geographic areas. Different diagnostic criteria and methods of data collection make it difficult to compare studies and to find reliable figures for the proportion of the population with the various diseases. Figures from Norwegian studies are largely based on questionnaires and should therefore be interpreted with caution.
Based on different studies, there appears to be a high incidence of asthma and allergic diseases in the population, and the number of cases appears to have increased over the last 20-30 years.
Asthma in children
Results from a cross-sectional study of children aged 7-14 from Nordland showed that the prevalence of self-reported asthma was 18 per cent in 2008 (Hansen, 2013). This corresponds with the results of a study among children in Oslo in 2003 where the prevalence was measured to be 20 per cent among ten-year-olds (Lødrup Carlsen, 2006). The prevalence in both studies was based on whether the child had ever had asthma.
Many preschool children have transient asthma-like symptoms, but do not develop asthma. This trend is supported by the reduction in the use of asthma medication seen in children after preschool age, see Figure 1. The diagnosis can be made with greater certainty from about five years of age.
Of those who develop asthma, about three out of four will have developed the disease before school age. A large proportion of these will become free of symptoms during school age, but new cases emerge during childhood, adolescence and adulthood.
Asthma in adults
Bronchodilators and anti-inflammatory agents are central in the treatment of asthma. Use of asthma medicines may reflect the proportion of the population with active asthma and who need treatment. Figures from the Norwegian Prescription Database are the best data we have about the prevalence of asthma in adults. The use of medicines is relatively stable until 30 years of age where a slight increase is seen for both sexes.
Figure 1 shows the proportion of the population who were prescribed medicine for asthma and asthma-like symptoms in 2005 and 2013. After 40-50 years of age, these medicines are also used in the treatment of chronic obstructive pulmonary disorder (COPD) and will therefore not represent treatment of asthma.
It is also shown that elite athletes in endurance sports such as skiing and swimming have an increased prevalence of asthma-like symptoms.
|Figure 1: Users of asthma medication in 2005 and 2013, per 1000 inhabitants, aged 0-44 years. Users are people who have collected at least one prescription of a medicine from a pharmacy during the year. Asthma medication includes corticosteroids, short- and long-acting beta2-agonists for inhalation, combination drugs with corticosteroids and beta2-agonists for inhalation, and leukotriene receptor antagonists. Source: Norwegian Prescription Database.|
Many children and young people have hay fever and atopic eczema
Several Norwegian studies have found that lifetime prevalence of hay fever (rhinitis) is about 25 per cent of school-aged children and 30 per cent among young people in puberty (Selnes, 2005; Hansen, 2013; Hovland, 2014). For adults, there is a reported incidence of 23 per cent for Western Europe (BAUCHAU, 2004).
The prevalence of atopic eczema is 17 per cent among two-year-old children, and between 21 and 33 per cent among children aged 9-11 years. These figures result from Norwegian studies in the period 2000-2009 (Selnes, 2005; Smidesang, 2009; Hovland, 2014). Corresponding figures are reported from studies in Sweden and Denmark (Mortz, 2001; Rönmark, 2009).
One in five adults has allergic contact dermatitis
The incidence of allergic contact dermatitis varies both over time and between countries. This is due to different usage patterns of products, as well as national regulations for the use of chemicals. In a review article from 2001, where studies from countries in Europe, North America and Asia were included, a prevalence of 7 per cent for allergic contact dermatitis was reported in 12-16 years old children (Simonsen, 2011). For adults in Scandinavia (years 1966-2007) there is a similar incidence of 21 per cent (Thyssen 2007).
Certain professions are particularly at risk for the development of skin allergy. This applies to occupations with frequent hand washing and work with skin irritants and allergenic substances, such as rubber chemicals, fragrances, preservatives, hair dye and metals.
Six to eight per cent of children have symptoms of food allergy
Reports from Europe and the US shows that 6-.8 per cent of young children and 3-4 per cent of adults have symptoms of food allergy with a positive allergy test (specific IgE in serum) (Gupta, 2007; Sicherer, 2010; Allen, 2012). However, there are many more who have allergic reactions to one or more foods than can be detected by the methods available (Sampson, 2005; Ben-Shoshan, 2010).
Figures 2a and 2b show foods that commonly give positive allergy test in children under five years and among people between 6 and 80 years. The figures are based on voluntarily submitted reports by doctors to the National Register of Severe Reactions to Food from 2000 to 2013. The Food Allergy Register receives between 80 and 100 reports including blood samples per year, but it is unknown whether these figures are representative of the Norwegian population (Namork, 2011; National Register of Severe Allergic Reactions to Food).
|Figure 2a: Foods that most commonly give a positive allergy test (specific IgE in serum) in the age group 0-5 years. The findings are consistent with those reported for Europe and USA. Source: National Register of Severe Allergic Reactions to Food.|
|Figure 2b: Foods that most commonly give a positive allergy test (specific IgE in serum) in the age group 6-80 years. The findings are consistent with those reported for Europe and USA. Source: National Register of Severe Allergic Reactions to Food|
Many have both asthma and allergy
There is a large degree of comorbidity between asthma and allergic diseases. In a Norwegian study of 10-year-olds, 87 per cent of children with hay fever (rhinitis) also had asthma, atopic eczema or conjunctivitis (itching / eye discharge), while 12 per cent of children had all these diseases (Bertelsen, 2010). In a Swedish study, hay fever was associated with asthma and / or eczema in 33 per cent of 12-year-old children (Ballardini, 2012). Furthermore, they found that asthma was associated with eczema and / or hay fever among 67 per cent of children (Ballardini, 2012).
A large European study found that the relative risk for comorbidity at eight years of age was 63 per cent if the child also had asthma, hay fever and eczema at four years of age (PINART, 2014). This suggests that children with two or more diseases in early childhood are at increased risk for continued comorbidity later in childhood.
Development over time and international comparison
The prevalence of asthma has increased in Norway. A study among children aged 7-14 from Nordland showed that the prevalence of self-reported asthma increased from 7 to 18 per cent from 1985 to 2008 (Hansen, 2013). In the study, the prevalence was based on whether the child had ever had asthma. In contrast to this, figures from the same time period for other Western countries such as Germany, Sweden and the United States show that the prevalence will soon level out, and in some countries it is even declining (Zollner IK, 2005; Akinbamia, 2009; Bjerg, 2010).
Results of a study in northern Norway show an increase in both the incidence of hay fever from 17 to 30 per cent in the period 1985-2000, and in atopic eczema from 13 to 21 per cent in the period 1985-1995 (Selnes, 2005). There was no further increase in the incidence of atopic eczema up until 2000 (Selnes, 2005). It is difficult to determine whether these trends are nationwide when the figures are based on only one study.
There are large international differences in the prevalence of hay fever and atopic eczema among children aged 6-7 years and 12-13 years (Asher, 2006). This is shown in the ISAAC study which includes many regions in major parts of the world. It was conducted in 1992-1998 and was repeated in 1999-2004. During the period between the first and second round of the ISAAC study, a slight increase in the incidence of hay fever worldwide was found (Asher, 2006). Several of the areas with high incidence at the first examination, however, had a lower incidence in the second round. For the age groups 6-7 and 12-13 years there was an increase in the incidence of atopic eczema in 84 and 59 per cent of the study centres, respectively.
Several reports suggest an increasing incidence of food allergy in Europe, but good documentation is lacking (Moneret -Vautrin, 2004; Burney, 2014).
An increased prevalence of pollen allergy in Europe and especially in Scandinavia will, due to climate changes, be expected to give a subsequent increase in both hay fever and pollen-related food allergy (so-called oral food allergy syndrome) (Eriksson, 2004; Madsen, 2005; Signs of Climate Change in Nordic Nature, 2009; D'Amato, 2013). These cross-reactions occur because allergens in pollen are similar to the proteins in the food.
Incidence changes in puberty
Boys have higher rates of asthma and allergies than girls until puberty. After puberty, the incidence among girls is higher than in boys. The reasons for the gender difference is uncertain, but hormonal changes during puberty and differences in environmental exposures may be significant (Almqvist, 2008; Chen, 2008).
There are no apparent age or gender differences in the incidence of allergic contact dermatitis.
Published literature suggests that there is a higher incidence of asthma among individuals with low socioeconomic status (Almqvist, 2005; Hammer-Helmich, 2014). There also appears to be a similar relationship between increased severity of asthma and socioeconomic status (Lang, 2010; Trupin, 2013). The results, however, are not clear-cut since the effect of socioeconomic status on the development of asthma seems to vary with the age of the child (Hafkamp-de Groen, 2012).
The relationship between socioeconomic status and allergic diseases is uncertain, various studies point in different directions (Almqvist, 2005; du Prel, 2006; Kotz, 2011; Hammer-Helmich, 2014). The reason for the conflicting findings is unknown but may be related to different methods of data collection, different definitions of socioeconomic status or different diagnostic criteria.
We have a lack of knowledge about regional differences in the prevalence of asthma and allergy in Norway. A study of schoolchildren living in Oslo, Upper Hallingdal and Odda in 1997 showed that there was little difference in the incidence of asthma, hay fever and eczema (Nystad, 1997).
Risk factors and prevention
The causes of asthma and allergic diseases are mostly unknown; hence, there are no interventions that can prevent these diseases.
Hereditary predisposition is an important factor. Results from twin studies have shown that 65-67 per cent of the variation in the tendency to develop asthma is largely attributable to heredity (Nystad, 2005).
Environmental factors may play a role in asthma and allergic diseases. Altered microbial diversity (bacterial composition in the body), respiratory infections early in life and exposure to allergens and environmental chemicals are considered to be possible causes of disease progression and / or deterioration. Other possible risk factors are obesity and inactivity.
It is important to distinguish between factors that can influence the development of disease among those who initially do not have asthma or allergies, and factors that may increase symptoms in those who are affected.
Those who have already developed the disease should:
- avoid exposure to what they are allergic to
- avoid or reduce exposure to factors that can worsen the symptoms, such as infections, allergens, air pollution (smoke, dust, exhaust fumes) and environmental chemicals.