Introduction

Cardiovascular diseases (CVDs) stand as the predominant cause of global deaths, with approximately 17.9 million deaths in 2019, which accounted for 32% of all worldwide deaths [1]. Of all cardiovascular diseases, 85% of the deaths were due to stroke and heart attack [1]. The burden of CVD worldwide is increasingly linked to environmental exposures [2]. The global health landscape has been increasingly marred by the nexus of air pollution and CVD, a duo responsible for a significant burden of morbidity and mortality across diverse regions. In the year 2020, it was observed that household air pollution (HAP) had associations with an estimated 3.2 million fatalities on an annual basis [3]. The combined impact of outdoor and HAP contributes to around 6.7 million premature deaths yearly [3]. According to a study, air pollution accounted for 8·0 percent of all Disability-Adjusted Life Years (DALYs) in 2021, making it the primary cause of disease worldwide [4]. Exposure to various diseases in individuals is commonly attributed to air pollution [5] which is considered a predominant environmental risk factor. Particulate matter (PM2.5) and HAP, primarily from the combustion of biomass fuels, have been identified as critical environmental determinants of elevated blood pressure and IHD, leading to a surge in global CVD deaths.

In the year 2019, air pollution accounted for 18% of the total number of fatalities within the geographical region of India [6]. Although India has experienced a decline in the death rate attributable to HAP, the death rate from outdoor air pollution has increased during 1990-2019 by 115%. Moreover, premature deaths and morbidity from air pollution resulted in an economic loss of about 14% of the GDP [6]. In India, open burning of dumped waste has been evidenced as a potential source of atmospheric pollution of gaseous and particle bound organic toxicants [7,8]. The primary contributors to outdoor particulate matter pollution in India include the burning of biomass in homes and businesses, dust carried by the wind, combustion of coal for power production, emissions from industries, burning of crop residues in agriculture, incineration of waste, construction work, operation of brick-making furnaces, emissions from transportation, and the use of diesel-powered generators [9,10]. Furthermore, the primary factor contributing to indoor air pollution is the use of solid fuels for cooking activities [11,12]. In India, the interconnection between air pollution and CVD emerges with stark clarity against the backdrop of its escalating cardiovascular disease epidemic. Studies have emphasized the association between personal exposure to pollutants like PM2.5 and CO with increased blood pressure among pregnant women and a broader CVD risk among the general population [10,13]. The situation is exacerbated by socio-economic development, where economic growth paradoxically aligns with increased CVD burden, possibly due to heightened exposure to air pollution from vehicular emissions and industrial activities [14]. This complex scenario presents a unique challenge for India, distinguishing its experience from global patterns and underscoring the need for targeted research and policy interventions.

Previous studies have underscored the pervasive impact of air pollution on cardiovascular health, highlighting an elevated risk across various cohorts from resource-poor settings in Guatemala, Peru, India, and Rwanda to the Eastern Mediterranean Region (EMR) [15,16]. Exposure to HAP and ambient particulate matter, particularly PM2.5 and black carbon, has been linked to increased blood pressure in pregnant women, a known risk factor for cardiovascular diseases [10]. Furthermore, long-term exposure to HAP has been associated with a rise in ischemic heart disease (IHD) mortality, emphasizing the adverse effects of air pollution on health [17]. A body of evidence underscores the critical impact of air pollution on cardiovascular health through mechanisms such as oxidative stress, inflammation, atherosclerosis, and vascular dysfunction, leading to an array of cardiovascular issues, including heart disease, stroke, and arrhythmias [18]. This global perspective is essential for understanding the profound implications of air pollution on CVD, necessitating a nuanced exploration of specific regional contexts to tailor public health interventions effectively.

India faces a unique challenge with a high ambient and HAP burden due to its reliance on solid fuels for cooking, industrial emissions, vehicular pollution, and agricultural burning. These factors contribute significantly to the national health burden, especially cardiovascular diseases. The rationale for focusing on the trends and patterns in deaths due to CVD attributable to air pollution, especially within the Indian context, stems from a critical gap in the existing literature and the urgent need to understand the evolving dynamics of this public health issue. Despite global awareness, the specific impact of air pollution on CVD in India requires further elucidation,

particularly considering the country's rapid urbanization, industrialization, and unique socio-economic landscape. Examining these trends can help us identify the age, period, and cohort effects of air pollution on health, assess the effectiveness of interventions over time, and understand the impact of economic development on air quality and public health.

Methods

Data Source

Data from India's State-Level Disease Burden Initiative was used in this analysis. which is a part of the Global Burden of Disease (GBD) Study. This gives information on the burden of 333 illnesses, injuries, and risk factors for each state in India from 1990 to 2019. In this investigation, we used information on air pollution-related mortality from cardiovascular disease, namely household and ambient air pollution, from a publicly accessible web link (https://vizhub.healthdata.org/gbd-compare/india#0). The current study used the 2019 database to methodically summarise and examine changes in CVD deaths attributable to air pollution in India between 1990 and 2019.

Statistical Analysis

Changes in Age Standardized Death Rates of cardiovascular disease attributable to ambient and household air pollution were calculated using joinpoint regression analysis [19]. The model provides the average percentage change (APC) and average annual percentage change (AAPC), where APC indicates the rate of change between two joinpoints and AAPC represents the overall rate of change. The estimated APC in each segment is averaged geometrically to get the AAPC, with the segment lengths acting as weights [20]. Intrinsic Estimator (IE) method was used to estimate the net age, period, and cohort effects on CVD deaths due to air pollution from observed age-specific death rates [21,22]. The degree of model fitting was evaluated using deviation, Akaike's information criterion (AIC), and the Bayesian information criterion (BIC). Standard error (SE) coefficients and risk ratios were calculated.

Results

Table 1 illustrates India's state-wise CVD burden for 2019, capturing incidence, mortality, and DALYs alongside age-standardized rates for these indicators. The data reveal substantial variability across different states, underscoring the country's heterogeneous nature of CVD impact. Uttar Pradesh and Maharashtra bear the brunt of the CVD epidemic, with the highest recorded incidences (1,230,923.77 and 891,281.63, respectively) and mortalities (328,687.54 and 276,151.82, respectively). In contrast, smaller states like Sikkim report much lower figures (3,971.77 incidences and 781.14 deaths), highlighting regional disparities in health outcomes. States with high DALYs, such as Uttar Pradesh (8,853,294.35) and Maharashtra (6,567,292.73), reflect not only high mortality but also significant morbidity, suggesting widespread and severe impact of CVD. States like Punjab, Tamil Nadu, and Karnataka exhibit high age-standardized mortality rates. For instance, Punjab shows the highest age-standardized incidence rate (833.91 per 100,000) and mortality rate (306.85 per 100,000), suggesting a disproportionately higher CVD burden relative to its demographic profile. Northeastern States like Mizoram and Nagaland have some of the lowest absolute numbers. Still, when standardized for age, the metrics tell a different story, with relatively higher morbidity and mortality rates than expected. Despite having better overall health indicators nationally, Southern States like Kerala and Andhra Pradesh show considerable CVD burden in absolute and age-standardized terms.

Table 1: State-wise deaths due to cardiovascular disease attributable to air pollution in Indian states incidence, mortality, and DALYs in 2019

Table 2 delineates the changes in the proportion of CVD deaths attributable to different types of air pollution from 1990 to 2019 across Indian states, segmented into HAP and ambient particulate matter (PM) pollution. The data indicate a significant transition in the burden of CVD deaths from household air pollution to ambient PM pollution over three decades. States with traditionally lower access to clean fuels and technology, like Bihar (23.28%), Chhattisgarh (28.08%), and Odisha (26.76%), reported high percentages, reflecting the prevalent reliance on solid fuels which emit particulate matter. The influence of ambient air pollution was considerably lower in rural and less industrialized states such as Arunachal Pradesh (2.93%) and Mizoram (4.84%), while Delhi displayed markedly higher levels at 8.07%. Delhi, being more urbanized even in 1990, had a significantly lower contribution from household air pollution at 2.14%, indicative of earlier adoption of cleaner fuels in urban centers. By 2019, a noticeable decline in the percentage of CVD deaths attributable to household air pollution from solid fuels is observed across most states, with significant reductions in states like Delhi, where it plummeted to 0.13% from 2.14% in 1990. However, the mortality contribution from ambient particulate matter surged from 8.07% in 1990 to 27.74% in 2019, suggesting a drastic deterioration in air quality.

Table 2. The proportion of CVD deaths attributable to air pollution among Indian states in 1990 and 2019

Similarly, HAP from solid fuels decreased in Delhi from 21.13% to 0.13%, reflecting changes in domestic energy use patterns. Delhi shows the most dramatic increase in CVD deaths attributable to Ambient Particulate Matter Pollution, soaring to 27.74% in 2019 from 8.07% in 1990, highlighting the severe impact of increased vehicular emissions, industrial activities, and urban congestion. States like Gujarat and Haryana also show a significant increased by 22.51% and 24.68%, respectively, correlating with their industrial growth and urban sprawl over the decades.

Table 3 offers an in-depth look at the sex-specific relative risks (RR) of CVD deaths attributable to air pollution, analyzed by age, period, and cohort effects. Relative risks are notably low across genders at younger ages, with males at 0.09 (95% CI: 0.08-0.10) and females at 0.11 (95% CI: 0.10-0.12) which increases with age, with individuals aged 85-95 years facing the highest risk (RR = 3.69; 95% CI 3.34-4.08 for total population), suggesting that older adults are particularly vulnerable to air pollution-related CVD outcomes. The analysis also highlights that females generally experience higher relative risks compared to males in older age groups. For instance, RR for females aged 85-89 is 4.03 (95% CI 3.71-4.37) versus males at 3.22 (95% CI 3.02-3.45).

In the early 90s (1990-94), there is relatively low risks at 0.85 (95% CI: 0.83-0.88) for the total population, however from 2005-09, the risk slightly increases to 1.01 (95% CI: 0.99-1.04) and more substantially by the latest period (2015-19) to 1.15 (95% CI: 1.12-1.17). Cohort effects reveal that earlier cohorts (1900-1924) experienced higher risks compared to later cohorts. Individuals born in 1900-04 had higher relative risk, i.e., RR: 3.06 (95% CI: 2.12-4.42), which dropped subsequently for individuals, and the 1985-89 cohort had the lowest risk of deaths from CVD attributable to air pollution 0.42 (95% CI: 0.37-0.47).

Table 3: Sex-specific relative risks of CVD death attributable to air pollutions in India due to age, period, and cohort effects

RR denotes the relative risk of CVD death attributable to a particular age, period, or birth cohort relative to the average level of all ages, periods, or birth cohorts combined. CI, confidence interval; AIC, Akaike Information Criterion; BIC, Bayesian Information Criterion. Age-standardised Death rates (Per 100,000 population)

Table 4 displays the trends in age-standardized CVD mortality rates and DALYs attributable to various sources of air pollution from 1990 to 2019, as determined by Joinpoint Regression Analysis. The AAPC of 1.13 indicates a net increasing trend in deaths linked to ambient PM pollution (95 percent CI 0.98-1.3). By comparison, deaths attributable to solid fuel-related home air pollution have been steadily declining, with an AAPC of -3.62. (95 percent CI -3.79 to -3.4). Most recently, there has been a decrease in the APC of air pollution-related deaths across all categories. DALYs linked to ambient particulate matter pollution have AAPC of 2.27 and show a net increasing trend (95 percent CI 2.15-2.38). On the other hand, with an AAPC of -3.71, the number of deaths associated with indoor air pollution from solid fuels continuously exhibits a notable decrease

trend (95 percent CI -3.83 to -3.59). The graph obtained from joinpont regression analysis has been shown in Figure 1.

Table 4: Trends in Age-Standardized death rates due to Cardiovascular disease attributable to air pollution in India from 1990 to 2019 using Joinpoint Regression Analysis

(a)

(b)

Figure 1: Trends in Age-Standardized rates due to Cardiovascular disease attributable to air pollution (a) Death rates (b) and DALYs in India from 1990 to 2019 using Joinpoint Regression Analysis

Figure 2 displays the ranks of age-standardized CVD death rates attributable to air pollution per 100,000 population for all ages across various states in India, comparing the years 1990 and 2019. States such as Delhi, Telangana, Andhra Pradesh, and Kerala have moved from lower levels of ASDRs to higher levels of ASDRs due to CVD attributable to air pollution. On the other hand, Mizoram, which had the lowest death rate in 1990 (ranked 1^st), still maintains the lowest death rate in 2019. However, Uttar Pradesh, Haryana, Bihar, Jammu Kashmir, and Uttarakhand have recorded a steep decline in ASDRs due to CVD deaths attributable to air pollution from 1990-2019.

Figure 2: Ranks of Age-Standardized CVD attributa to air pollution death rate per 100,000 population for all ages in 1990 and 2019 in India

Discussion

The current study explores the burden of CVD attributable to air pollution across various states in India, analyzing data from 1990 to 2019. Our results showing an increase in CVD mortality related to ambient PM and a decrease in CVD deaths linked to reductions in HAP align well with broader research trends [23,24]. Additionally, a study by Cohen et al [25] emphasized that ambient PM2.5 was a significant mortality risk factor globally, highlighting a rising burden due to inadequate air quality management in low and middle-income countries​. Similarly, a study highlighted a global decrease in CVD risks associated with improved household energy utilization [26], which reflects our findings of declining HAP impacts due to advancements in cleaner cooking technologies​. Consistent with previous findings [18,27], our study underscores the significant role of ambient particulate matter (PM2.5) in increasing the risk of CVDs. This is aligned with the evidence that ambient air pollution, particularly PM2.5, contributes to oxidative stress, inflammation, and atherosclerosis, leading to cardiovascular morbidity and mortality. Our study also highlights a significant reduction in CVD deaths attributable to household air pollution, a trend supported by Adekoya and colleagues [26], who found a consistent decline in health risks associated with improved household energy use in low- and middle-income countries (LMICs). This reflects successful public health initiatives aimed at reducing exposure to HAP through adopting cleaner cooking technologies, which has effectively mitigated CVD outcomes.

Reflecting on the economic analysis from the India State-Level Disease Burden Initiative [6], our findings about the substantial health burdens of air pollution in India are confirmed. Our study

also highlights regional disparities in CVD burden, with higher burdens observed in industrially advanced states. This is consistent with a finding which suggested an inverse relationship between state-level human development indices and APACVD burden, indicating that economically thriving states might also be those most affected by air pollution due to higher industrial and vehicular activities [14]. The increasing impact of ambient particulate matter, particularly noted in states with growing industrialization and urban sprawl like Maharashtra and Tamil Nadu, underscores the urgent need for implementing robust air quality management policies to curb pollution sources and mitigate their health impacts. A study has reported the highest mortality share for ‘X’ class cities and north India [28], in line with our higher mortality concentration in Delhi.

In line with our findings, a study reported a considerably high mortality burden in cities such as Chandigarh, Ludhiana, Dehradun, Patna, Kolkata and Delhi, etc [28]. Indigenous emission sources account for 76% of all premature deaths in the Indo-Gangetic Plain region, which includes cities like Delhi, Dehradun, Ghaziabad, Kanpur, Lucknow, and Patna [29]. Cross-border transportation and natural resources account for the remaining 15% of premature deaths [29]. These variations in the prevalence of CVD among areas with varying levels of socio-economic development primarily pointed to an imbalance in air quality management and the provision of CVD healthcare [24]. The economic impact, particularly in states with lower per-capita GDP, emphasizes the dual challenge of health and economic growth hindered by air pollution. These economic insights are critical for policy-makers, underlining the need for targeted air quality improvements to bolster public health and economic productivity.

Results from age, period, and cohort analysis indicated that the risk of CVD increases with age, with older cohorts experiencing higher risks and more pronounced health impacts. This age effect likely reflects cumulative exposure to air pollution and the physiological vulnerabilities that escalate with aging. It was observed that at an older age, the relative risk of death attributable to air pollution is higher, especially among women. In contrast, at younger ages, the death rates are higher for males than females. Another factor contributing to the higher prevalence of CVD in the elderly population is their susceptibility to PM2.5 exposure [30]. This was due to the fact that older individuals had longer exposure times and cumulatively more harmful effects of ambient PM2.5 on their cardiovascular systems [31]. The elderly's physiologic reserve and toxicodynamic restoration were hampered by their frailty and weakened immune systems [32].

Furthermore, older people are more likely to have preexisting chronic lung and cardiovascular diseases, making them more susceptible to PM2.5 exposure [33]. The period effects observed suggest that there have been fluctuations in CVD incidence related to environmental and policy changes over the study periods. Notably, recent periods have shown worsening trends, potentially linked to increased industrialization and urbanization, leading to heightened air pollution levels. Cohort effects reveal a more complex picture, with earlier cohorts (born in the 20th century) experiencing higher CVD risks, which gradually decrease in later cohorts for both sexes. This trend aligns with improving healthcare, lifestyle changes, and perhaps shifts in exposure patterns due to evolving pollution control policies. In major cities with a population of one million or more, Nair and colleagues estimated an improvement of 1.01 percent in premature death in major cities due to air pollution by 2024. This improvement can be attributed to policy intervention through the National Clean Air Action Programme [28].

Our analysis aligns with findings that identify vulnerable subpopulations that suffer disproportionately from air pollution-related CVDs, particularly in Asian countries [34,35]. Elderly populations and those with morbidities are at higher risk, necessitating targeted interventions to protect these high-risk groups. There is consistent evidence linking short-term exposure to particulate matter and nitrogen oxides to elevated risks of hypertension, myocardial infarction (MI), and stroke (both fatal and nonfatal). On the other hand, prolonged exposure to PM2.5 was principally associated with a higher risk of incident MI, atherosclerosis, hypertension, stroke, and stroke death [27]. Despite global efforts to improve air quality, the upward trend in CVD burden from ambient air pollution calls for reinforced policy actions. Previous research suggests that stringent air pollution control measures can derive significant health benefits, particularly in rapidly urbanizing and industrializing regions like India [5,25].

Conclusions

Supporting information

None

Ethical Considerations

None

Acknowledgments

None

Funding

This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

Author contribution statement

All authors contributed equally and attest they meet the ICMJE criteria for authorship and gave final approval for submission.

Data availability statement

Data included in article/supp. material/referenced in article.

Additional information

No additional information is available for this paper.

Declaration of competing interest

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

References