Overall Asthma Prevalence
Asthma is a prevalent long-term respiratory disease that impacts millions of people across all age groups in the US, with an approximate 8–9% prevalence rate [14]. According to our estimated investigation, 8.7% of the population in the United States suffers from asthma. This percentage has varied in prior U. S publications, ranging from less than 3% to more than 20% [15–18]. Asthma prevalence varies by nation and is impacted by a variety of variables, including genetics, environmental circumstances, healthcare infrastructure, and lifestyle.
More than 8 million individuals in the UK, or almost 12% of the total population, have an asthma diagnosis. Nevertheless, while some individuals may have outgrown the condition, 5.4 million are currently undergoing treatment for asthma [19]. In Australia, the prevalence of asthma is 11%, much higher than the worldwide incidence of 4% [20]. In 2011–12, 3.8 million Canadians (or 10.8% of the population) had been diagnosed with asthma [21]. In Sweden, 8.3% of people had a physician-diagnosed case of asthma [22]. Most asthma cases in the Gulf States are reported from Saudi Arabia [23]. Asthma affects around 24% of the population [23]. The rates for Kuwait and Qatar are 16.8% and 19.8%, respectively [23]. This is followed by 13% in the UAE and 10% in Oman [23]. In adults in Ireland [24], the frequency is 7%, whereas in children, it is 21%. In 2018, there were 2.4% of people in Indonesia [25] who had asthma, and 57.5% of those people had relapses. In Africa [26], the average asthma prevalence was 6%.
Then, our investigation prevalence approximates developed countries' reports and discovered that the reported asthma prevalence is higher in developed countries than in developing countries, explaining that in developed countries, there may be more asthma awareness, better access to healthcare, and more robust healthcare systems. Conversely, asthma may go undiagnosed and untreated in underdeveloped nations for a variety of reasons, such as lack of knowledge, restricted healthcare access, and financial limitations.
Asthma Prevalence by Gender
The results of our research showed that the prevalence of asthma has significantly increased among females. Almost studies and reports found the same result [27–29], which could be explained by the effects of female sex hormones on lung cells, and changes in hormone levels during puberty, menstruation, pregnancy, and menopause can affect airway function, which among women with asthma, up to 30–40% have reported worsening of asthma symptoms at specific times of the menstrual cycle in some series [30]. Furthermore, research indicates that women often have narrower airways, which may increase their vulnerability to airflow blockage and asthma symptoms [31]. Additionally, since women spend more time indoors, they may be more susceptible to interior allergens, especially if they have domestic duties. Dust mites, pet dander, and mold are examples of indoor allergens that may aggravate asthma symptoms.
Asthma Prevalence by Age
Although the odds of having asthma among individuals above 60 years were roughly 1 compared to adults, the highest prevalence of asthma among elderly individuals was observed in our study. This finding is consistent with previous studies that have reported similar results [32,33]. The immune system of the aged changes, known as immunosenescence, which may lead to a greater vulnerability to respiratory infections and inflammation [34]. Older people may acquire and have worsening symptoms of asthma because of this compromised immune system. An aging-related disorder called "inflammaging" is linked to persistent low-level inflammation [35]. Asthma's defining characteristics, airway inflammation and hyperresponsiveness, might result from this ongoing inflammation. Elderly people get increasingly exposed to environmental elements such as pollution, allergies, and respiratory irritants [36]. Long-term exposure to these variables raises the likelihood of developing asthma by causing airway damage and sensitization. Comorbid health disorders, such as cardiovascular disease or chronic obstructive pulmonary disease (COPD), are more common among the elderly [37].
Asthma Prevalence by Race
Non-Hispanic whites exhibited the highest asthma prevalence, while the lowest asthma prevalence indicated among Mexican Americans, and align with our findings some studies in California, New Mexico, and Arizona had reported a lower risk of asthma and respiratory diseases among Mexican-American adults [38,39]. Genetic and biological differences among ethnic groups can influence their susceptibility to asthma. Certain genetic variations may make individuals prone to developing asthma or experiencing asthma-related symptoms [40]. Cultural practices, dietary habits, and health behaviors can vary among ethnic groups and impact asthma risk [41]. For example, dietary choices that include an abundance of fruits and vegetables, common among some Hispanic populations, may have protective effects against asthma. In addition, the migration patterns of different ethnic groups can play a major role in the difference of asthma prevalence [42].
Asthma Prevalence by Marital status:
Married individuals showed the highest asthma prevalence. The quality of the marital relationship and the presence of social support within marriage can influence asthma. For instance, a troubled or stressful marriage may contribute to increased asthma prevalence due to psychological stress, while a supportive and happy marriage may have a protective effect. Married individuals may be more likely to live with a partner who smokes, which can exacerbate asthma symptoms. Additionally, dietary habits and physical activity levels can be influenced by marital status. Other studies have not found a significant difference in asthma prevalence between married individuals and those who are unmarried [43,44].
Asthma Prevalence by Family income
Our analysis reported high asthma prevalence among those with low income. Studies consistently demonstrate that asthma is more prevalent among individuals with lower household incomes [45,46]. Factors like substandard housing, exposure to environmental pollutants, and limited access to healthcare can contribute to this disparity. Lower-income individuals often face disparities in healthcare access and quality, which can lead to inadequate management of asthma and increased prevalence [47]. They may have limited access to preventative care, medications, and asthma education. Low-income communities are more likely to be exposed to environmental triggers for asthma, such as air pollution, allergens, and tobacco smoke [48]. These exposures can exacerbate asthma symptoms and contribute to higher prevalence rates.
Asthma Prevalence by BMI
On this study, the highest asthma prevalence was observed among obese individuals. Numerous studies have observed a positive association between obesity, particularly higher BMI, and asthma prevalence [49,50]. Obesity is characterized by chronic low-grade inflammation, with the adipose (fat) tissue serving as an active source of pro-inflammatory molecules. This inflammatory state can extend to the airways, leading to airway inflammation. This systemic inflammation can exacerbate the inflammatory processes associated with asthma, making it more likely for asthma to develop and become more severe in obese individuals [51]. Increased fat in the chest and abdomen can limit the expansion of the lungs and diaphragm. This decreased lung volume can lead to reduced airflow and increased airway resistance, which are characteristic features of asthma [52].
Asthma Prevalence by Smoking
Higher prevalence of asthma was observed among smokers in this study. Previous studies have consistently shown that both active smoking (smoking cigarettes) and exposure to secondhand smoke (passive smoking) are associated with an increased risk of developing asthma [53,54]. Cigarette smoke contains numerous harmful chemicals and irritants that can directly damage the airways [55]. These irritants can trigger inflammation in the respiratory system, leading to airway constriction and mucus production. Smoking generates oxidative stress in the lungs, which can damage cells and tissues [56]. This oxidative stress can contribute to airway inflammation and bronchial hyperreactivity, key characteristics of asthma [56]. Smoking can disrupt the immune system's balance, leading to an enhanced response to allergens and respiratory infections. Exposure to secondhand smoke can make individuals, especially children, more sensitive to environmental allergens and respiratory irritants [57]. This heightened sensitivity can increase the likelihood of asthma development or exacerbation.
Asthma Prevalence by other respiratory conditions
Most of the asthma patients in this study suffered from other respiratory conditions like emphysema, chronic bronchitis, and COPD. According to previous study, asthma frequently coexists with other respiratory diseases [58,59]. This coexistence can complicate the management of these conditions and lead to poorer health outcomes [58]. Asthma, emphysema, chronic bronchitis, and COPD share common risk factors such as smoking, exposure to environmental pollutants, and genetic predisposition [60]. Smoking is a well-established risk factor for emphysema, chronic bronchitis, and COPD [61]. It is also associated with an increased risk of developing and exacerbating asthma [61]. The structural changes in the airways, such as airway remodeling, are common features of asthma and COPD [62]. These changes can result in increased airway hyperresponsiveness and decreased lung function, contributing to symptoms in both conditions. Emphysema also involves structural damage to the lungs.
Clinical implications:
The variation in asthma prevalence across different countries highlights the need for global awareness and standardized healthcare practices. Developed nations with higher asthma prevalence may serve as models for effective asthma management, emphasizing the importance of awareness, access to healthcare, and robust healthcare systems in reducing the burden of asthma.
Understanding the impact of hormonal changes on airway function is crucial. Tailoring treatment plans and education programs to address the unique challenges faced by women, such as hormonal fluctuations and increased exposure to indoor allergens, can improve asthma outcomes.
Recognizing the impact of immunosenescence and inflammaging on asthma symptoms is crucial. Regular monitoring, personalized treatment plans, and awareness campaigns targeting the elderly can enhance asthma care.
The strong association between obesity and asthma prevalence underscores the importance of incorporating weight management strategies into asthma care. Healthcare providers should prioritize weight reduction interventions, and obesity-related inflammation.
The higher prevalence of asthma among smokers highlights the critical role of smoking cessation programs in asthma prevention and management. Physicians should prioritize smoking cessation interventions, especially among vulnerable populations like children and adolescents, to reduce the risk of asthma development and exacerbation.
Limitations:
The reliance on NHANES data may raise concerns about the representativeness of the sample, potentially leading to the underrepresentation of specific subgroups within the U. S population. The cross-sectional design of the study, while informative about associations, cannot establish causality, leaving questions about the direction of relationships. Moreover, the study utilizes self-reported data, including self-reported physician diagnoses of asthma, introducing the possibility of recall bias and misclassification of asthma cases. While the analysis highlights the significance of age, shortness of breath, and respiratory conditions, it may overlook other unmeasured confounding variables. Comparative analyses with other studies, such as the European Community Respiratory Health Survey (ECRHS), offer valuable context but also pose challenges due to differences in study design and populations.
Additionally, its generalizability to other countries may be limited, given variations in culture, healthcare systems, and environmental factors. Lastly, the measurement of shortness of breath, while identified as significant, needs more detailed examination, potentially impacting the reliability of the findings. In addition, the COVID-19 pandemic forced the halting of NHANES 2019–2020 field activities in March 2020, after data had been gathered in 18 of the 30 survey sites in the 2019–2020 sample. Data from the previous cycle (2017–2018) were integrated with the obtained data, which were not nationally representative, to generate a pre-pandemic data file covering the period from 2017–March 2020. The pre-pandemic data set for March 2020 to March 2017 underwent a unique weighting procedure. Neither the 2017–2018 data alone nor the 2019–March 2020 data alone will provide nationally representative findings using these sample weights, nor are they suitable for independent studies of the 2019–2020 data.