Kate from Oz

Asthma Client Research


requested literature review for AES client

Client requested prioritization of weather-related and environmental Asthma triggers, with demographic risks as secondary in a summary format. All information comes from peer-reviewed journals. My primary search locations for information included JStor, PubMed, Medline, Google Scholar, and the Wichita State University library. This is the resultant research provided to the client.

Asthma Triggers and Risk

There are many factors that increase the prevalence of patients seeking treatment (hospitals or clinics) for an asthma attack including weather, air pollution, allergies, demographic differences, geographic location, and lifestyle. Beyond the well-known triggers like air pollution and aeroallergens (pollen), there are many interesting triggers including thunderstorms, river valleys, urban living, and obesity. Each of the following categories will address the current research on that asthma trigger(s) with bibliographic information at the end.

            In locations around the world, there have been isolated cases of a significant increase in asthma patients seeking treatment following a thunderstorm. Researchers found that this correlation between thunderstorms and asthma attacks requires a very specific set of conditions due to typical thunderstorms not inducing asthma responses. What is most frequently hypothesized: dry updrafts carry whole pollens into the high humidity at the cloud base of a large sferic dense thunderstorm where pollens may rupture and cold downdrafts carry pollen fragments to ground level. (D’Amato 14) Sferics are lightning flashes. Researchers have found that thunderstorms with high density sferics show increases in asthma attacks even after zero or low pollen averages but significant increases in attacks with high pollen averages. This amplification of thunderstorms and high pollen has a greater effect on adults compared to children. (Newson 684)
            Major thunderstorm-asthma outbreaks that have been studied include Birmingham UK (1983), London (1994), Melbourne AUS, Wagga Wagga AUS (1997), and Naples Italy. (D’Amato) Researchers found that urban residents were more affected than rural residents. (D’Amato 12)

            River valleys, especially with urban environments, present an interesting situation involving the exacerbation of asthma symptoms. Researchers found that “weather characterized by high levels of humidity together with low and similar air and dew point temperatures have an adverse effect on respiratory health. These meteorological conditions are associated with formation of mists and fogs or high levels of airborne water droplets especially in lower altitude areas of river valleys.” (Price 217) Reasoning for increases associated with river valleys is that the downslope airflows associated with differences in valley temperatures could contribute to an increase of pollution from high elevation areas to the bottom of the river valley with intensification from high levels of water droplets and droplet born pollutions. (Price 234) Further findings from this research show meteorological conditions, low or similar air temperature and dew point as well as high relative humidity, are common during mist/fog episodes or high levels of airborne water droplets. (Price 239) When there are high levels of air pollution or pollen and increased levels of moisture droplets, asthma will be exacerbated due to more aeroallergens and air pollution getting deeper into patients’ lungs. Further evidence of increased rates of emergency room visits for asthma was found in Utah valleys when winter temperature inversions occur. (Beard)

            In multiple studies, the researchers found higher rates of asthma attacks in urban populations versus rural populations. Price found increased admission rates for asthma patients in urban areas of the United Kingdom which was linked to higher air pollution levels. D’Amato found the same results when studying aeroallergens. Patients living in urban areas tended to be more affected by plant-derived respiratory disorders than those living in rural areas with possibly an increase in pollen allergens due to exposure to environmental pollution. (D’Amato 12) While more researchers found a link with higher asthma hospitalization rates in urban areas, Akinbami found no difference in asthma rates between metropolitan and nonmetropolitan areas.

            One of the most impressive studies linking air pollution and asthma hospitalizations/treatment occurred when Beijing hosted the 2008 Summer Olympics. The city significantly reduced traffic congestion in the weeks leading up to and including both the Olympics and Para-Olympics. Li compared the average number of outpatient visits for asthma during the pre-Olympic period to the Olympic period. There was a 41.6% overall decrease in outpatient visits during the Olympics. The main difference that could account for this massive decrease is the heavy restrictions placed on vehicle traffic in the city. Air pollution measurements confirm a significant reduction in air pollution levels during the Olympics.
            Air pollution has been found to directly affect asthma sufferers around the world of all age groups and is potentially the most common trigger. (Goksel) Air pollution includes CO, NO2, O3, SO2, particulate matter, etc. While all age groups are significantly affected by air pollution, children (0-14 years) have higher relative risk of hospitalization compared to adults (16-65). (Ko) Silverman found that children age 6-18 years were specifically at the highest risk for asthma hospitalization, but Villeneuve found young children (2-4 years) at the highest risk. The elderly had a shorter lag time to developing asthma exacerbation when exposed to high air pollution compared to those aged 65 and under, and were at higher hospitalization risk (Ko, Villeneuve). (Ruffoni, Tosca, Ko, Delamater)
            The lag effect is also highly important when looking at the relationship between air pollution and asthma hospitalizations. The elderly had the shortest lag time between peak air pollution and asthma exacerbations. Overall, Nastos found that there was statistically significant air pollution lag time (7-8 days) and asthma hospitalizations. Villeneuve also found significant relationship with multi-day lag times and asthma hospitalization.
            Multiple researchers found interesting correlations with air pollution and aeroallergens (pollen). Villeneuve found that when adding aeroallergens, there was not a significant effect on air pollution and asthma hospitalizations. Cakmak identified an association between aeroallergens and asthma hospitalizations, with an increased risk related to higher air pollution.

            Along with air pollution, aeroallergens (pollen, pet dander, etc.) are a significant trigger for asthma hospitalizations and treatment. Pollen from flowering plants and grasses seem to be the most dangerous for asthma patients. A 10 year study from Italy found that pollen from Parietaria (from the Nettle family), was most strongly associated with asthma hospitalizations in both children and adults. (Ruffoni, Tosca) Researchers found that high tree pollen counts coincided with higher risks of asthma hospitalization in the Bronx (NYC). (Jariwala) Erbas found that as grass pollen increased, the same day and one lag day risk for childhood asthma hospitalization increased as well. Risk of pollen-induced asthmatic symptoms can be further exacerbated by exposure to air pollution. (Cakmak)
            Weather can also have a significant effect on aeroallergens and asthma hospitalization. Greater humidity, fog, mist, and thunderstorms all increase the amount of airborne moisture that can trap pollen, pollen starches, aqueous phase oxidation of air pollution, etc. that can then be more easily inhaled, and find its way deeper into the lungs, which can lead to great risk for asthma attacks and needed treatment. (Price)

Many researchers studying asthma triggers found significant correlation with the various seasons, heat waves, and cold spells. Researchers also found measurable differences with different age groups and these specific conditions. Weather change is the second most common asthma trigger. (Goksel)

Cold Finnish researchers did a population study based on 1623 young adult subjects whose family participated in a multi-year questionnaire study starting in 1991 with follow-ups in 1997 and 2011. (Hyrkas 64) Cold-related respiratory symptoms, including wheezing and cough, increased up to 23.1% for subjects with asthma compared to 2.0/5.8% among healthy subjects. (Hyrkas 66) In another population study, the researchers found that cold-related breathlessness was found among 51-72% of subjects with asthma living in Lapland, the northernmost region of Finland. (Hyrkas 69) In Japan with adult subjects, Abe found that cold temperatures are related to an increased risk of significant exacerbation of asthma. Scheuerman found that over a three year period in Israel, peak asthma admissions rates were in winter months while lowest rates were in the summer. In Shanghai, researchers found a significant relationship between cold temperature spells and pediatric asthma treatment. The lower the temperature, the higher the risk for children with asthma to have attacks. (Guo 1) Further studies found that asthma-related doctor appointments peaked in February. (Buckley 4) On the other side of the world, Greece, there is a significant association between bronchial asthma admissions with O3 two day lag during the winter season. (Nastos) Jariwala confirms the Greece conclusions by finding asthma-related hospital visits to be highest in winter with a positive correlation with air pollution (SO2 and NOx). Yet there is research that finds no statistically significant relationship between air pollution and asthma clinical treatment in the period of autumn and winter. (Villeneuve 4)

Heat Researchers studying extreme temperature effects on asthma hospital admission rates found male children and children aged 0-4 were most susceptible to effects on asthma during heat waves. (Xu 730) Many research studies did find that summer had the lowest overall rates of asthma treatments compared to the other seasons. (Nastos, Scheuerman, Buckley)  For children, there was a correlation between the summer and increased O3 and PM2.5 (particulate matter) with higher rates of asthma attacks. (Silverman) When factoring in high air pollution (especially vehicular traffic related pollution), all age ranges experience increased risk for asthma attacks in the summer months. (Villeneuve 6)

Spring/Autumn Peak Especially for researchers using population studies to learn more about asthma triggers, many found asthma hospitalizations/treatment peak in the Spring and Autumn. This did not change when looking at various age groups; it is consistent for both children and adults. (Ruffoni, Tosca, Nastos, Jariwala) Reasoning behind the Spring peak is often contributed to significant increases in aeroallergens, including pollen, exacerbating asthma symptoms. Researchers studying adults in North Carolina did come to different conclusions; they found a decreased risk for emergency room asthma visits during the Spring and Autumn months. (Buckley) The researchers also found that September was unique for high hospital admissions for asthma attacks in children (especially toddlers and elementary aged children). These studies should not discredit the reseachers who found winter/cold to be most significant on asthma hospitalization/treatement rates. It would be interesting to further look into how the environment effected the peak season for asthma in each of the studies that studied effects of seasons on asthma risk.

Misc Nastos did find a positive correlation with cooling power, relative humidity, and wind speed and the risk of asthma hospitalizations for children. There was a negative correlation with discomfort index, air temperature, and absolute humidity. A different study found that fluctuations in humidity and temperature influence risk for asthma hospitalizations. (Mireku)

Demographics and lifestyle attributes addressed will include age, gender, income, ethnicity, US regions, and weight.

Gender/Age Female adults are at a slightly higher risk to develop asthma when compared to males. The difference typically ranges from 1-2% higher. (Akinbami, Hyrkas, Villeneuve, Ginde) The opposite is actually true for children. Male children have a higher risk of developing asthma compared to female children. (Xu, Akinbami) When studying asthma hospitalizations or asthma exacerbation, children, especially aged 0-4 years, are the most likely to have to seek treatment or visit the hospital. (Akinbami, Ko, Silverman, Scheuerman, Villeneuve, Ginde, Nastos) At the opposite end of the spectrum, the elderly are also at greater risk for asthma hospitalizations and significantly higher asthma death rate compared to the population as a whole or adults (18-65 years). (Ko, Villeneuve, Akinbami)

Ethnicity In the United States, white persons have been experiencing a steady decline in asthma prevalence compared to other ethnicities. Puerto Ricans, African-Americans, American Indians, and non-Mexican Hispanics have higher asthma prevalence when compared to white persons. Asians and Mexican-Americans had some of the lowest rates of asthma. What was truly shocking was the asthma death rate for African-Americans compared to white Americans. The asthma death rate is 75% higher for African-Americans. The researchers did not give a reason for this high rate compared to white Americans. (Akinbami, Ginde)

Income/Region Families with combined income below, at, or near the poverty level have higher asthma prevalence when compared to families/persons with incomes of at least 200% of the poverty level. Near poverty level is considered families/persons with income 100-200% of the poverty level. (Akinbami) When studying regions of the United States, the Northeast and Midwest had higher rates of asthma prevalence when compared to the West and South regions. (Akinbami, Ginde)      

Obesity Obesity is a major risk factor for asthma but the reasons and mechanisms for it are still poorly understood. Asthma may contribute to obesity, but weight gain and obesity may trigger latent asthma. (Huovinen, Beuther) Some studies have found a slightly higher risk of asthma for obese women compared to obese men, but this would follow the slightly higher risk of asthma for women in the general population. More importantly, weight loss has been shown to reduce the risk of developing asthma and decrease asthma symptoms. “If significant weight loss could be achieved in the population of overweight and obese individuals, it could be estimated that new asthma cases in United States adults might fall as much as 250,000 per year.” (Beuther 663, Sideleva, Huovinen) In males, increasing height was associated with lower asthma incidence even for males with BMI classification of overweight or obese. Leisure time physical activity had a mildly protective effect on asthma risk, and higher education decreased the risk too. For women, these factors were non-significant or marginal, and they did not have the protective effects of height, physical activity, and higher education as shown in men. (Huovinen 275) On the opposite side of obesity is the small subgroup of underweight Americans. This group, comprised of mainly women, have a similar risk of asthma as overweight women. Previous studies have shown underweight persons are prone to respiratory problems. Just like the link between obesity and asthma is poorly understood, the link between asthma and underweight persons is also poorly understood. (Huovinen 278)

Risks and triggers for asthma hospitalization are highly varied. Air pollution, aeroallergens, age, cold, and obesity have some of the most significant effects on both asthma prevalence and risk of asthma hospitalization and treatment. Age and aeroallergens are often beyond a person’s or government’s control but many different changes could make life significantly easier for asthmatics. This includes trying to continue to decrease air pollution in the environment, being at a healthy weight since obesity and underweight individuals are at significantly higher risk of developing asthma. Staying inside during Spring thunderstorms to minimize of the risk of asthma attacks and hospitalization. Weather has also been shown to have a significant impact on asthma hospitalization risk especially when looking at heat waves, cold spells, lightning-heavy thunderstorms during high pollen days, and rain and high relative humidity allowing for moisture rich air to make it easier for humans to inhale aeroallergens and air pollution. Risks for developing asthma, but also having asthma-related hospitalizations, are complicated by the high variety of triggers and factors.

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