Risk factors for asthma across India: Results from global asthma network (GAN) phase I study

Abstract

Introduction:

This study aimed to assess the risk factors and triggers predisposing to asthma in Indian children and adults.

Methods:

The Global Asthma Network Phase I study was a multicentre, international, school, and questionnaire-based cross-sectional study conducted across the world with nine centers in India from 2017-18, the current study being analysis of the Indian data.

Results:

There were 20084 children, 25887 adolescents, and 81296 adults from 9 sites across India. The adjusted odds ratio (AOR) and 95% confidence interval (CI) for atopic factors were as follows: parental history of asthma in adults (AOR 2.88, CI 2.21–3.75), hay fever in children (AOR 2.05, CI 1.62–2.58), and hay fever in adolescents (AOR 1.65, CI 1.40–1.94). Environmental triggers such as exposure to damp spots in the home (AOR1.28, CI 1.05–1.55), antibiotics consumption (AOR 1.80, CI 1.30–2.51), paracetamol taken during pregnancy (AOR 1.23, CI1.02–1.49), and laying on a woollen blanket in the first year of life (AOR 1.67, CI1.34–2.03) were the risk factors predisposing to current wheeze in the children. Risk factors for current wheeze in the adolescents included passage of trucks in front of the house (AOR 1.20, CI 1.04–1.39), and pet animal exposure (AOR 1.32, CI 1.14–1.53); and in the adults included damp spots in houses (AOR 1.61, CI 1.47–1.77), and the use of coal or kerosene or cow dung as a cooking fuel (AOR 1.48, CI 1.28–1.71). Personal factors such as the history of pneumonia in the children (AOR 1.71, CI 1.36-2.15); wheezing after exercise (AOR 1.45, CI 1.23–1.69), hospitalization in the past year (AOR 2.85, CI 2.61–3.59) and caesarean birth (AOR 1.28, CI 1.07–1.53) in the adolescents were associated with current wheeze. India-specific triggers included consumption of bananas (AOR 1.34, CI 1.10–1.63), curd (AOR 1.49, CI 1.23–1.82), packed crunchies (AOR 1.23, CI 1.03–1.48), ice-creams (AOR 1.31, CI1.12–1.53) in adolescents and use of mosquito repellents in adults (AOR 1.11, CI 1.01–1.22).

Conclusion:

The study identifies genetic, environmental, personal health, and dietary risk factors for asthma in India, underscoring the need for public health measures to improve air quality, promote dietary awareness, and reduce indoor hazards.

INTRODUCTION

Asthma is a significant public health concern in India, with its prevalence varying across regions and age groups. The international study of asthma and allergy in childhood (ISAAC) was a multicentre, international, school and questionnaire-based study conducted in three phases (1995, 1998, 2001–03, respectively) following a uniform approach.[1] The phase III ISAAC study revealed a prevalence of childhood wheeze in about 6% of children and adolescents in India.[2] ISAAC was reformulated as the global asthma network (GAN) study in 2012, the GAN phase I was conducted across multiple centers in the world in 2017–18 including 9 centers in India.[3] GAN phase I revealed a prevalence of current wheeze as 3.16–3.63% in children, adolescents, and adults.[3]

The prevalence of asthma varies partly due to varied environmental triggers such as weather, pollens, local customs, food habits, and inherent geographical differences in disease burden. The prevalence and associated environmental triggers vary as per the geographical region. Previous studies have found an association of symptoms of asthma with smoking[2] truck traffic near the house,[2] open fire cooking,[4] dampness in homes,[5] fast food intake,[6] obesity,[7] and paracetamol/antibiotic use.[8,9] Breastfeeding[10] and intake of fresh fruits and vegetables impart a protective effect. With the change in industrialization, economy, and environment many of these factors have changed in prevalence with an increase in breastfeeding practices and fresh fruits; a reduction in antibiotic/paracetamol use, exposure to farm animals, and fast food.[3] India’s diverse demographic profile is characterized by unique environmental factors that influence respiratory health. Additionally, cultural practices, traditional beliefs, and dietary habits also play a role in shaping perceptions of respiratory illnesses. One significant aspect is the prevalence of myths surrounding environmental factors and their impact on asthma. For instance, there is a common belief that consuming curd, cold beverages, or ice creams can trigger or worsen asthma symptoms. Understanding the true environmental triggers of respiratory diseases and addressing widespread myths is crucial for ensuring evidence-based management.

The primary aim of the study was to ascertain the environmental triggers that are associated with symptoms of asthma in children, adolescents and adults and to evaluate India-specific triggers of asthma such as bananas, guava, ice cream, curd, and mosquito coil/incense sticks.

METHODS

The GAN phase I methodology was improvised from the ISAAC phase III and has been described in detail previously.[3] This was a multi-center, multi-country, questionnaire, and school-based study. Asthma Bhawan, Jaipur, India an independent research institute was the national data coordinating center for the study in India. The study was approved by the institutional ethics committee as well as was registered in the clinical trial registry, in India (CTRI/2018/02/011758).

In 2017–18, nine centers in the 13–14 yr age group and 8 centers in the 6–7 yr age group participated across the country. Amongst these, seven were the same centers as previous studies, two (Kolkata and Mysuru) new centers participated for better geographical representation. Before the initiation of the study, all investigators met at the NDCC, Jaipur they were oriented and trained for the study. Subsequently, the field workers and data entry operators were trained at the Indian Institute of Health Management and Research (IIHMR), Jaipur. Each center procured the total list of schools including government and private schools in their area, the schools were randomly selected from this list. Each city was divided into four zones, and a proportion of schools was randomly selected from each zone. The randomization was done at IIHMR, Jaipur. Invitations were sent to school principals, and only those who consented were included in the study. The schools were contacted and consenting schools were then approached for the study. If a particular school refused the next on-list school was approached. The field workers distributed the questionnaires to the children. The 13–14 yr age group children filled in the questionnaire and returned immediately; they took their parent’s questionnaire home. The younger children took their and their parent’s questionnaire home to be filled and brought the next day to school. Consent was obtained passively from the children and adults. Refusals were communicated to the field workers either by phone call or written note. Patient confidentiality was maintained by keeping the questionnaires anonymous and each child was assigned a code which the child shared with the parent.

The questionnaire was designed to capture symptoms of asthma, allergic rhinitis, conjunctivitis, and eczema along with a history of exposure to various environmental triggers which could exacerbate asthma and allergic diseases. The environmental questionnaire used in the Indian centers had additional India-specific questions about certain foods such as bananas, guava, curd, ice creams, cold drinks, cakes, packed crunchies and the use of air coolers and mosquito coils/incense sticks at home. There were three questionnaires for the 6-7 yr age group, 13-14 yr age group, and adults respectively (Supplement A, B, C). They were available in English, Hindi, Marathi, Bengali, Punjabi, Malayalam, and Kannada (the translations were certified back-translated). Coding of the data and data entry was done as instructed in the GAN Protocol. The data was entered by the respective centers except for the Kottayam center which was entered by the National Coordinating Center. Double data entry was done for 10% of data for quality checks and any discrepancy if present was mutually by the IIHMR Team. Any discrepancies or missing data were clarified by contacting the parents. The consolidated data from all centers was sent to the GAN global center in Auckland, New Zealand for initial quality check and subsequently to the main data center in London, United Kingdom, where the data was again checked for consistency and duplicity. The clean data set was locked and used for analysis. Parent and child data were merged to analyze parental history as a risk factor for current wheezing and severe asthma in children. The presence of current symptoms was correlated with the environmental triggers to determine associations.

The symptoms of asthma were adjudged by the following questions: “Did you have any wheeze in the past 12 months?”-WHEZ12. “Was this child’s asthma confirmed by a doctor??”-ASTHDOC, “Have you ever had wheeze?”-WHEZEV. Severe asthma was diagnosed in subjects who had more than four attacks of wheezing in the past year or sleep or speech interruption due to wheezing during the past year.

Statistical analysis

The sample size targeted for each age group at each center was 3000 with potentially 6000 adults including father and mother. This sample size gives sufficient power to detect a 5% difference between two centers with 99% certainty (at a 1% level of significance). Using SPSS Version 27, Bangalore, India, descriptive analysis was used to describe demographics, prevalence rates of different symptoms, and health-related data. Continuous variables data were presented using N, mean ± SD, and categorical variables presented as frequency and percentage. Bivariate and multivariate analyses were performed to estimate the impact of environmental and health-related factors on the presence of current wheeze, and severe asthma. Bivariate analysis was performed using χ2 tests for categorical variables (categories without order such as male or female) and student t-tests for continuous variables (infinite number of values within a range). Results of χ2 tests were presented in the form of Odds Ratio (OR) with 95% confidence intervals. Unadjusted P values of less than 0.05 were considered significant and were further included for multiple comparisons. Multivariate analysis was performed using a binary logistic regression model to identify the variables associated with the presence of current wheeze or severe asthma. Binary logistic regression was used to determine the relationship between independent variables (predictors) and dichotomous outcomes (wheeze “yes” or “no”, severe asthma “yes” or “no”). Furthermore, the impact of multiple independent variables could be assessed simultaneously. The results were presented using adjusted OR and 95% CIs.

RESULTS

Of the 22947, 26808, and 81798 participants in the 6–7 yr age group, 13–14 yr age group, and adults respectively, 20084, 25887, and 81296 participants had complete data sets available. The center-wise distribution of symptoms of asthma shows that the prevalence of current wheeze varies from 0.35% in Bikaner to 8.54% in Chandigarh in the 6-7 yr age group; 0.89% in New Delhi to 6.62% in Jaipur in adolescents; and 0.88% in New Delhi to 6.02% in Kottayam in adults [Figure 1].

Figure 1.

Bar diagram showing the prevalence of current wheeze and severe asthma in the children (Panel a), adolescents (Panel b) and adults (Panel c) across the nine centers in India in Global asthma network study

Atopic factors such as the presence of allergic rhinitis, hay fever ever, and parental history of asthma; environmental triggers such as exposure to farm animals in the first year of life, damp spots in the home, antibiotics taken to treat infections, paracetamol taken during pregnancy, lay on sheepskin/pure woollen blanket in the first year of life, and smooth floor without rug were the risk factors predisposing to current wheeze in the 6-7 yr age group [Table 1]. Personal factors such as chest infections in the first year of life, and every diagnosis with pneumonia; and food triggers such as once or twice-per-week consumption of pulses, pasta, fast food, and soft drinks were associated with current wheeze in the children. Children with exclusive breastfeeding for more than six months, daily physical activity, fruits once a week or more, cooked vegetables once a week or more, bread consumption, olive oil consumption once or twice per week, and dairy products consumed once or twice per week were less likely to have current wheeze.

Table 1.

The association of various environmental factors with current wheeze and severe asthma in children ages 6-7 years old with adjusted odd’s ratio (AOR)

6–7 Year Children
Current Wheeze				Severe Asthma
Risk factors		AOR (95% CI)		Risk factors		AOR (95% CI)
Atopic factors
Allergic Rhinitis		2.00 (1.45–2.75)		Allergic Rhinitis		1.73 (1.09–2.72)
Hay fever ever		2.05 (1.62–2.58)		Hay fever ever		2.30 (1.69–3.13)
Parental history of Asthma		2.88 (2.21–3.75)		Parental history of Asthma		3.53 (2.56–4.86)
Environmental factors
Moisture or damp spots in the house		1.28 (1.05–1.55)		Mother smoked during pregnancy		0.30 (0.11–0.77)
Paracetamol taken during pregnancy		1.23 (1.02–1.49)		Cooler/AC used		0.76 (0.58–0.99)
Antibiotics taken to treat chest infection		1.80 (1.30–2.51)
Lay on a pure woollen blanket in the first year of life		1.67 (1.34–2.03)
Regular contact with Farm animals during the first year of life		1.49 (1.09–2.03)
Smooth floor without rug		1.34 (1.09–1.65)
Personal factors
Ever diagnosed with pneumonia/bronchopneumonia		1.71 (1.36–2.15)		Ever diagnosed with pneumonia/bronchopneumonia		2.19 (1.64–2.93)
Chest infection in the first year of life		1.73 (1.42–2.12)
Exclusive Breastfeeding >6 months		0.68 (0.52–0.89)
Physical activity daily in hours		0.63 (0.47–0.84)
Food factors
Pulses consumed once or twice per week/Most or all days in last 12 months		1.42 (1.12–1.80)		Margarin consumed once or twice per week/Most or all days in last 12 months		1.44 (1.06–1.96)
Pasta consumed once or twice per week/Most or all days in last 12 months		1.31 (1.02–1.69)		Milk consumed once or twice per week/Most or all days in last 12 months		1.57 (1.18–2.09)
Fast food consumed once or twice per week/Most or all days in last 12 months		1.47 (1.07–2.02)
Soft drink consumed once or twice per week/Most or all days in last 12 months		1.42 (1.06–1.91)
Bread consumed once or twice per week/Most or all days in last 12 months		0.68 (0.54–0.86)
Olive oil consumed once or twice per week/Most or all days in last 12 months		0.65 (0.50–0.85)
Dairy Products consumed once or twice per week/Most or all days in last 12 months		0.78 (0.63–0.97)
Vegetables cooked once or twice per week/Most or all days last12 months		0.77 (0.58–0.90)
Fruit once or twice per week/Most or all days last 12 months		0.81 (0.66–0.99)

In the adolescent group [Table 2], atopic factors such as the history of allergic rhino-conjunctivitis, hay fever ever, eczema ever, and parental history of asthma; environmental triggers such as frequent or almost all-day passage of trucks, and pet animal exposure in the past year were associated with current wheeze. Personal factors associated with current wheeze in this age group included caesarean birth, wheezy chest after exercise, and being hospitalized in the past year. Food triggers for current wheeze in adolescents include once or twice per week consumption of potatoes, bananas, curd, ice cream, and packed crunchies.

Table 2.

The association of various environmental factors with current wheeze and severe asthma in children ages 13-14 years old with adjusted odd’s ratio (AOR)

13-14 Year Children
Current Wheeze				Severe Asthma
Risk factors		AOR (95% CI)		Risk factors		AOR (95% CI)
Atopic factors
Allergic Rhino-conjunctivitis		1.70 (1.39-2.08)		Allergic Rhino-conjunctivitis		2.04 (1.58-2.63)
Hay fever ever		1.65 (1.40-1.94)		Hay fever ever		1.95 (1.59-2.38)
Eczema ever		1.53 (1.27-1.85)		Eczema ever		1.65 (1.31-2.08)
Parental history of Asthma		2.84 (2.31-3.49)		Parental history of Asthma		2.69 (2.06-3.52)
Environmental factors
Pet animal in the past 12 months		1.32 (1.14-1.53)		Pet animal in the past 12 months		1.43 (1.19-1.73)
Trucks pass through the street: frequently or almost the whole day		1.20 (1.04-1.39)
Personal factors
Child’s chest sounded wheezy during or after exercise		1.45 (1.23-1.69)		Child’s chest sounded wheezy during or after exercise		1.53 (1.26-1.850
Hospitalized in last 12 months		2.85 (2.61-3.59)		Hospitalized in last 12 months		3.49 (2.68-4.56)
Child Borm LSCS (caesarean)		1.28 (1.07-1.53)
Food factors
Banana trigger symptoms*		1.34 (1.10-1.63)		Banana trigger symptoms		1.36 (1.07-1.73)
Curd trigger symptoms*		1.49 (1.23-1.82)		Curd trigger symptoms		1.45 (1.13-1.86)
Pack crunchy trigger symptoms*		1.23 (1.03-1.48)		Pack crunchy trigger symptoms		1.39 (1.12-1.73)
Ice-cream trigger symptoms*		1.31 (1.12-1.53)		Guava trigger symptoms		1.32 (1.03-1.69)
Soft drink consumed once or twice per week/Most or all days in last 12 months		0.70 (0.59-0.82)		Meat consumed once or twice per week/Most or all days in last 12 months		1.40 (1.13-1.74)
Potato consumed once or twice per week/Most or all days in last 12 months		1.19 (1.03-1.38)

*India specific questions

In the adult group [Table 3], the atopic factors for current wheeze included hay fever ever and eczema ever; and environmental triggers such as moisture or damp spots in the houses, use of coal/kerosene/cow dung as cooking fuel, and use of mosquito coils/incense sticks in the house. Secondary education, previous use of tobacco, and current use of tobacco were the personal factors associated with current wheezing in adults. Food triggers such as consumption of once or twice per week of rice or pulses were less likely to have current wheeze in this age-group.

Table 3.

The association of various environmental factors with current wheeze and severe asthma in adult parents with adjusted odd’s ratio (AOR)

Adults
Current Wheeze				Severe Asthma
Risk factors		AOR (95% CI)		Risk factors		AOR (95% CI)
Atopic factors
Hay fever ever		4.99 (4.56–5.46)		Hay fever ever		6.09 (5.43–6.85)
Eczema ever		1.72 (1.55–1.90)		Eczema ever		1.63 (1.43–1.87)
Environmental factors
Moisture or damp spots in the house		1.61 (1.47–1.77)		Moisture or damp spots in the house		1.77 (1.57–1.99)
Fuel used for Cooking- Coal/Kerosine,/Dung, wood, crop residue		1.48 (1.28–1.71)		Fuel used for Cooking- Coal/Kerosine,/Dung, wood, crop residue		1.48 (1.23–1.79)
Any type of fuel for cooking		1.41 (1.25–1.59)		Any type of fuel for cooking		1.41 (1.21–1.65)
Used cleaned Cooler/AC in house*		0.67 (0.61–0.74)		Used cleaned Cooler/AC in house		0.61 (0.54–0.69)
Mosquito coils/incense sticks in the house*		1.11 (1.01–1.22)
Personal factors
Primary Education		1.13 (1.13–1.46)		Primary Education		1.25 (1.06–1.47)
Secondary education		0.83 (0.72–0.95)		Secondary education		0.78 (0.65–0.93)
Ever used tobacco but not now		1.65 (1.31–2.07)		Currently using tobacco		1.82 (1.59–2.08)
Ever used and now too tobacco		1.59 (1.43–1.77)
Food factors
Seafood consumed once or twice per week/Most or all days in last 12 months		1.20 (1.09–1.33)		Seafood consumed once or twice per week/Most or all days in last 12 months		1.33 (1.14–1.54)
Rice consumed once or twice per week/Most or all days in last 12 months		0.85 (0.78–0.94)		Rice consumed once or twice per week/Most or all days in last 12 months		0.79 (0.69–0.89)
Pulses consumed once or twice per week/Most or all days in last 12 months		0.84 (0.76–0.94)		Pasta consumed once or twice per week/Most or all days in last 12 months		0.79 (0.69–0.93)
				Nuts consumed once or twice per week/Most or all days in last 12 months		1.15 (1.01–1.31)

*India-specific questions

The associated factors for severe asthma in all the age groups are elaborated in Tables 1-3, respectively.

DISCUSSION

A myriad of environmental triggers were associated with the prevalence of asthma including the presence of allergic rhinitis, eczema, hay fever, the presence of asthma in parents, exposure to farm animals in the first year of life, chest infections in the first year of life, wheezing in the first year of life, damp spots in the home, made changes in the home, laying on sheep skin as an infant, eating curd and ice-creams, caesarean section birth, and mosquito coils.

A difference was noted in the prevalence of asthma in the age groups in between different centers also which has been noted in the worldwide data as well.[11] The regional difference in the prevalence of asthma may be due to regional differences in climate, humidity, vegetation, pollen, air pollution levels, genetic variation, and diet. Kottayam has lesser variations in temperature due to the proximity of coastal regions with more humidity. Jaipur had a high prevalence in adolescents and adults; a city with a dry, arid climate with sandstorms in the summer months. Sand particles in sandstorms have been associated with low lung functions in patients with asthma.[12] Despite this, Bikaner, another desert city known for its extreme climatic conditions and frequent sandstorms, exhibited a relatively lower prevalence of asthma symptoms—a finding that remains challenging to explain. One possible reason for this unexpected observation could be the influence of other environmental factors that differ between Bikaner and regions with higher asthma prevalence. For instance, Bikaner may have comparatively lower urban air pollution levels, which is a well-established trigger for respiratory conditions. However, further research is needed to systematically assess these factors and determine their potential impact on respiratory health in Bikaner.

The current study reinforced the association of allergies and asthma in the family, with parental history of asthma being a strong risk factor for current wheezing and severe asthma in children and adolescents [Tables 1 and 2].[13] A familial history of asthma, allergic rhinitis, and hay fever was strongly associated with symptoms of asthma; so was the presence of atopy in the same subject, emphasizing the inter-relationship of the allergic diseases. The presence of childhood infections and wheezing were also found to be associated with symptoms of asthma predominantly in the 6–7 yr age group. This is rather a contentious relationship, where some reports have found a positive association between childhood infections and the development of asthma depending on the type, duration of infection, and host susceptibility.[14] Other reports, however, after longitudinal assessment have failed to find an association between the two.[15]

Damp spots in the house were found to be associated with current wheeze in children and adults. The common culprit fungi include Alternaria, Cladosporium, Aspergillus, and Penicillium.[16] Cohort studies have documented a sevenfold greater increase in the risk of asthma in children residing in homes with heavy fungal growth.[17,18] Exposure to farm animals and pet animals was found to be associated with symptoms of asthma in children and adolescents respectively [Tables 1 and 2]. Contradictory findings have been reported in previous studies. A systematic review has reported that early-life pet exposure leads to the development of asthma.[19] However, the birth cohort PIAMA study has not found early pet exposure predisposing to asthma in children up to 8 years of age.[20] Previous studies have supported the hygiene hypothesis and farm animal exposure in childhood has been reported to be protective in preschool and school-aged children against the risk of asthma.[21] ISAAC phase III study showed a positive association between early life exposure to farm animals and the development of asthma in non-affluent countries.[22]

Laying on sheep skin provides heavy and assorted microbial exposure at an important point in the development of the immune system. A study from New Zealand found that laying on sheepskin in the first year of life increases the prevalence of current asthma by 1.9 times.[23] Our study, however, noted that laying on woollen blankets as an infant predisposes to symptoms of asthma in the 6–7 year age group of children in India (AOR 1.67, 95% 1.34–2.03). Many of these factors may not act alone but in conjunction with other factors such as socio-economic conditions, climate, and food habits.

In the ISAAC Phase III study, children exposed to open-fire cooking had 2.17 times higher odds of experiencing wheezing in the past year, while adolescents had 1.35 times higher odds.[4] However, this study did not assess the impact on adults who are exposed to open-fire cooking for longer durations and with greater intensity. In our current study, we found that using fuels such as coal, kerosene, cow dung, and wood is associated with a 1.48 times higher risk of developing current wheeze and severe asthma. This highlights the need to consider long-term exposure and its effects, especially among adults who may face chronic respiratory issues due to prolonged and intense exposure to these pollutants, emphasizing the need for clean fuel in the kitchen. Caesarean section birth was associated with the development of asthma in adolescents (AOR 1.28, 95%CI 1.07–1.53) in the current study. However previous meta-analyses have revealed normal birth to be protective against the development of asthma and atopy in childhood.[24] However, again most of the studies analysed in the systematic review were done in Europe.

There is a widespread belief that ice, fizzy drinks, fried food, and nuts can trigger asthma. Therefore, we included relevant questions in our study and analyzed the data accordingly. These questions though not present in the GAN questionnaires used in the other countries, were imbibed in the Indian questionnaire. A positive association was noted with the consumption of curd (AOR 1.49, 1.23-1.82) and ice creams (AOR 1.31, 1.12–1.53) in the 13–14 year age group. In a previous questionnaire-based study conducted in the United Kingdom, Asian children attributed their symptoms of asthma to food such as ice, fizzy drinks, fried food, and nuts.[25] Six of these children demonstrated bronchial responsiveness after consuming the food.[25] Another more recent study from Ecuador found that children consuming either cold drinks or specific foods (milk or nuts) reported more attacks of asthma leading to emergency visits.[26] However, a positive food mix Ig E was not found associated with either attacks or recurrences. A positive association of symptoms of asthma in adults was noted with exposure to mosquito coils and incense sticks (AOR 1.11, 95%CI 1.01–1.22).[13]

Given the stark regional disparities in asthma prevalence and the clear role of environmental triggers, policymakers must take immediate action to implement targeted interventions in high-risk areas. Strengthening air quality regulations, controlling dampness in houses and offices, promoting the widespread adoption of clean cooking fuels, and launching public health campaigns to mitigate known asthma triggers should be national priorities. Strategies need to be planned to provide healthcare support in regions with a higher prevalence of asthma symptoms and to minimize exposure to known risk factors, particularly for individuals with a family history of asthma and allergies.

The study is associated with the limitations of being a questionnaire study including recall bias, with patients often forgetting the symptoms of the past and also not correctly identifying their symptoms. Furthermore, response bias may arise when participants report exposures linked to common myths about triggering wheeze or cough, such as ice cream and cold drinks. There have been previous questionnaire-based studies that have been subjective and have been instrumental in generating data. The uniform methodology with the previous ISAAC studies and across the world helped in generating a large database for comparison across a wide time frame. The second limitation was the lack of an objective marker for the diagnosis of asthma such as spirometry. However performing spirometry for such a large number of individuals would have been logistically unfeasible, with normal spirometry not ruling out asthma. The third limitation was the presence of selection bias. Though every attempt was made to minimize this bias, by randomly selecting schools in each center, all parts of the country could not be covered. The rural areas were under-represented in the study due to logistic limitations.

CONCLUSION

This has been the largest study in recent times across India, recruiting children, adolescents, and adults. The study has provided valuable insights into the prevalence of symptoms of asthma with varied prevalence in different parts of the country. A possible interplay of environmental and genetic factors could have been responsible for this difference. Myriad environmental triggers were found to be associated with symptoms of asthma including allergic history in parents, exposure to farm animals in the first year of life, damp spots in the home, laying on sheep skin as an infant, tobacco use, use of kerosene/wood/cow dung as cooking fuel, use of mosquito coils/incense sticks, chest infections in the first year of life, wheezing in the first year of life, caesarean section birth, and food such as curd, and ice-creams. Strategies need to be planned to provide healthcare support in regions with a higher prevalence of symptoms of asthma and avoid incriminating exposures, particularly in individuals with a positive family history of asthma and allergies. Policymakers must urgently address these issues by enforcing air quality regulations, promoting clean cooking fuels, and launching targeted public health initiatives. While this study provides crucial epidemiological insights, future research should focus on unraveling the genetic predisposition to asthma in different populations to better understand regional variations in prevalence.

Conflicts of interest

There are no conflicts of interest.

Funding Statement

Cipla foundation.