Global trends and projections of tracheal, bronchial, and lung cancer (TBL) associated with secondhand smoke (SHS) exposure in women: insights of the Global Burden of Disease (GBD) study 2021 from 1990 to 2021 and prediction to 2035

Abstract

Background

Tracheal, bronchial, and lung cancer (TBL) is a leading cause of cancer-related deaths, with 2.5 million new cases globally in 2022—the highest incidence of any cancer. However, a comprehensive global analysis of the disease burden of TBL attributable to secondhand smoke (SHS) exposure among women is currently lacking. To address this gap, we used the most recent data from the Global Burden of Disease (GBD) 2021 study to assess the global, regional, and national burden from 1990 to 2021 across 204 countries and territories, to analyse temporal trends, and to project the potential trajectory up to 2035.

Methods

The data have been sourced from the 2021 GBD study, which encompass specific health indicators across 204 countries and territories from 1990 to 2021. Utilising the analytical framework of frontier analysis, we sought to quantify the unrealised potential for disease burden reduction at equivalent development levels across nations. In addition, we identified the theoretically optimal performance frontier and employed decomposition analysis to evaluate the contribution of each influencing factor. Moreover, utilising this framework, a Bayesian age-period-cohort model was adopted for the scientific projection of the disease’s trajectory through 2035.

Results

In 2021, the number of deaths among women worldwide attributable to SHS exposure for TBL was 41,062.72 [95% uncertainty interval (UI): 5,535.86 to 78,059.16], with DALYs totalling 996,309.39 (95% UI: 1,359,881.8 to 1,907,078.95). The global burden of this disease was predominantly concentrated among women aged 50–80 years. Amongst the 204 countries and territories examined, China demonstrated the highest ASDR and ASDAR for TBL related to SHS exposure among women [2.50 per 100,000 population (95% UI: 0.34–4.80) and 59.78 per 100,000 population (95% UI: 8.19–114.91), respectively]. In the context of the five socio-demographic index (SDI) regions, the highest standardized death rate change was observed in the high-SDI region (−2.00; 95% confidence interval: −2.18 to −1.82). Furthermore, an increase in the burden of female TBL attributable to SHS exposure was noted as SDI levels rose.

Conclusions

The global burden of TBL among women exposed to SHS is declining, with both ASDR and ASDAR falling between 1990 and 2021. Projections indicate a further reduction in deaths and DALYs by 2035. Nevertheless, SHS continues to be a significant public health concern, requiring enhanced global collaboration and targeted interventions to mitigate its adverse effects on women’s health even further.

Highlight box.

Key findings

• Global age‑standardized death and disability-adjusted life years rates for female tracheal, bronchial, and lung cancer (TBL) attributable to secondhand smoke (SHS) declined from 1990 to 2021, but absolute deaths rose. Burden is highest in women aged 50–80 years, with China leading in death counts.

What is known and what is new?

• SHS is a well‑established risk factor for TBL, especially in women.

• This is the first comprehensive analysis of SHS‑attributable TBL burden in women using Global Burden of Disease 2021 data (204 countries and territories, 1990–2021) with projections to 2035.

What is the implication, and what should change now?

• SHS remains a major public health threat in middle‑ to high‑socio-demographic index regions and older women. Current screening guidelines based mainly on age and smoking history may miss high‑risk women with heavy SHS exposure; policymakers should strengthen smoke‑free policies and consider SHS as a screening risk factor.

Introduction

Tracheal, bronchial, and lung cancer (TBL) is the leading cause of cancer-related deaths. According to the latest data from the International Agency for Research on Cancer (IARC) of the World Health Organization (WHO), the global cancer burden continues to rise. In 2022 alone, there were 20 million new cancer cases worldwide, resulting in 9.7 million deaths. Lung cancer remains the most common type of cancer, accounting for 2.5 million new cases—one-eighth of all new cancer diagnoses. Furthermore, lung cancer caused 1.8 million deaths, accounting for 18.7% of all cancer-related fatalities and ranking as the leading cause of cancer-related mortality (1).

Exposure to tobacco is associated with a variety of adverse health effects and is one of the most significant preventable causes of cancer (2). Smoking is responsible for around 30% of cancer deaths (3). In regions where smoking is common, 80% to 90% of TBL cases are smoking-related, increasing the risk of developing TBL-related cancers by up to 20 times (4). Secondhand smoke (SHS) is also a major contributor to TBL, causing over 890,000 premature deaths worldwide each year. Women and children are particularly vulnerable to SHS, often being exposed to it in both the home and public places. Research shows that exposure to SHS is the third biggest risk factor for women’s health (5). Furthermore, a cohort study involving 600,000 Norwegians found that women are more susceptible to lung cancer than men when exposed to the same level of tobacco smoke (6).

Therefore, to gain a more profound understanding of the disease burden of TBL among women exposed to SHS, an analysis was conducted of data from 204 countries and territories between 1990 and 2021. This comprehensive evaluation of SHS’s impact on the TBL burden among women aims to furnish scientific evidence for the development of effective public health policies and interventions to mitigate the adverse effects of SHS on female TBL.

Methods

Research design

The present study, based on the most recent data from the Global Burden of Disease (GBD) 2021, aims to assess the GBD (TBL) attributable to SHS exposure among women in 2021 and to analyze trends from 1990 to 2021.Furthermore, the study endeavored to project the potential trajectory of this disease burden through to 2035. A detailed disaggregation and comparison of the data was conducted by age, region and country.

In accordance with the GBD risk factor classification, “secondhand smoke exposure” is delineated as the exposure to SHS within the domestic environment or the occupational setting. It is hypothesised that all individuals living with daily smokers are at risk of exposure to SHS. In this study, non-smokers are treated as the primary subjects of concern with regard to SHS exposure. In this analysis, former smokers and occasional smokers were classified as non-smokers. Moreover, due to the absence of data in the GBD database on TBL cases among women under 25 years old attributable to SHS exposure, data for this age group were excluded from consideration in this study.

Data resource

The present study is based on data resources from GBD 2021, a collaborative project initiated by numerous organisations, academic institutions, research centres, and governments. The GBD 2021 study encompasses health risk assessments for a total of 371 diseases and injuries, in addition to 88 risk factors. According to the 11th edition of the International Classification of Diseases (ICD), TBL is coded as ICD-11 C24–C25. We retrieved estimates of deaths and disability-adjusted life years (DALYs) attributable to SHS exposure via the GBD2021 website (https://gbd2021.healthdata.org/gbd-results/), using the search terms “Estimate: Risk factor; Risk: Secondhand smoke; Cause: Tracheal, bronchial, and lung cancers, Measure: Deaths and DALYs; Metric: The number and rate of occurrence of secondhand smoke as a contributing factor to tracheal, bronchial, and lung cancers is indicated”.

Definition of glossary

Age-standardized rates (ASRs)

The ASR is a critical tool for correcting comparative biases arising from differences in age distribution across populations or time periods, thereby enabling valid comparisons between regions, countries, or time points with different demographic structures. It is important to note that ASR is not appropriate for comparing different age groups within the same population, for which age-specific rates or absolute counts should be used. In this study, ASRs were adopted in order to eliminate the impact of age structure on death and DALYs statistics. The ASR calculation is based on matching the age structure of the study population with that of the GBD global standard population, achieved through a weighted average of the raw rates. The application of ASR resulted in the standardisation of the age distribution of deaths and DALYs. Consequently, the age-standardized death rate (ASDR) and age-standardized DALYs rate (ASDAR) were calculated (7). This process facilitates a more precise evaluation of health status and assessment of the efficacy of public health measures. In this study, statistical significance is defined as a 95% confidence interval (CI) (8). All mortality and epidemiological parameters (including DALY-related indicators) are reported with 95% CIs to account for uncertainties in data collection, model development, and statistical estimation.

Socio-demographic index (SDI)

The SDI is a composite indicator that measures the socioeconomic, demographic, and developmental levels of different countries and territories. The index is calculated by integrating key factors such as per capita gross domestic product (GDP), educational attainment, and total fertility rate. In the GBD 2021 study, the SDI scoring range was refined to 0 to 100, thereby providing a more precise assessment. The classification of 204 countries and territories worldwide has been undertaken on the basis of adjusted SDI scores, with the objective of meticulously categorising them into five tiers: low SDI, lower-middle SDI, middle SDI, upper-middle SDI, and high SDI regions (1,9). This classification facilitates a deeper understanding of socioeconomic development levels across regions and reveals the potential association between the TBL burden attributable to SHS exposure among women and socioeconomic development levels. By comparing SDI values across different countries and territories, researchers and policymakers can more clearly identify health inequalities and develop targeted public health strategies accordingly.

Statistical analysis

Estimated annual percentage change (EAPC)

The temporal trends were analysed by calculating the EAPC from 1990 to 2021. To account for the non-negative and skewed nature of rate-based data, the linear regression model was applied to the natural logarithm-transformed age-standardized rates (ASDR or ASDAR) rather than the raw rates (10). The resultant figure is representative of the percentage change in the rate value per year. In the event of the EAPC being greater than zero and its 95% CI not including zero, this is indicative of a statistically significant upward trend; conversely, it is indicative of a significant downward trend (11).

Decomposition analysis

Decomposition analysis is a statistical method that identifies the specific roles and contributions of individual factors by breaking down overall changes, thereby revealing the key drivers influencing the overall variation. In this study, we applied decomposition analysis to examine the interrelationships between the burden of disease and three sociodemographic factors: ageing, epidemiological transition, and population size (12). The R software platform was utilised to conduct a systematic assessment of the impact of these three factors on changes in disease burden. Furthermore, in order to provide a more comprehensive illustration of the contribution of these factors to the disease burden, comparative analyses were conducted based on different SDI levels. This was done to gain deeper insights into their roles across varying socioeconomic contexts.

Prediction

In order to predict mortality and DALYs for the period 2021–2035, the present study utilised Bayesian age-period-cohort (BAPC) and integrated nested Laplace approximation (INLA) packages in order to guarantee the precision and reliability of the projections (13-15).

Software

All analyses and visualizations were conducted in R version 4.3.3.

Results

Global burden

According to the results of an analysis of the GBD database, in 2021 a total of 41,062.72 [95% uncertainty interval (UI): 5,535.86 to 78,059.16] deaths from TBL attributable to SHS among women across all age groups were recorded globally. The ASDR was 0.89 (95% UI: 0.12 to 1.69) per 100,000 population. The overall mortality trend demonstrated a decline (EAPC, −0.57; 95% UI: −0.66 to −0.49), with DALYs totalling 996,309.39 (95% UI: 135,988.18 to 1,907,078.95). The ASDAR was 21.81 (95% UI: 2.98 to 41.75) per 100,000 population, with a consistent downward trend in overall ASDAR (EAPC, −0.89; 95% UI: −0.98 to −0.81) (Table 1).

Table 1. Global, regional, and age-specific burden of tracheal, bronchial, and lung cancers associated with female secondhand smoke exposure in 1990 and 2021: deaths, and DALYs stratified by GBD region and their corresponding age-standardized rates.

Regions	Death						DALYs
	Death cases (95% UI), 1990	ASDR per 100,000 (95% UI), 1990	Death cases (95% UI), 2021	ASDR per 100,000 (95% UI), 2021	EAPCs (95% CI), 1990–2021		DALYs (95% UI), 1990	ASDAR per 100,000 (95% UI), 1990	DALYs (95% UI), 2021	ASDAR per 100,000 (95% UI), 2021	EAPCs (95% CI), 1990–2021
Global	20,854.23 (2,761.76, 37,839.66)	0.98 (0.13, 1.78)	41,062.72 (5,535.86, 78,059.16)	0.89 (0.12, 1.69)	−0.57 (−0.66, −0.49)		577,952.84 (76,273.91, 1,045,073.19)	26.56 (3.50, 48.03)	996,309.39 (135,988.18, 1,907,078.95)	21.81 (2.98, 41.75)	−0.89 (−0.98, −0.81)
SDI
High	5,944.30 (747.83, 11,283.39)	0.98 (0.12, 1.87)	6,326.95 (831.53, 12,318.96)	0.57 (0.07, 1.10)	−2.00 (−2.18, −1.82)		156,587.47 (19,746.14, 295,948.24)	27.76 (3.51, 52.25)	141,148.66 (18,480.15, 272,306.53)	14.47 (1.89, 27.79)	−2.28 (−2.46, −2.09)
High-middle	7,282.14 (965.87, 13,477.77)	1.30 (0.17, 2.41)	16,332.03 (2,200.69, 31,053.13)	1.50 (0.20, 2.86)	0.28 (0.17, 0.38)		201,298.90 (26,695.89, 373,039.40)	36.18 (4.78, 66.98)	392,588.33 (53,808.57, 748,087.14)	37.60 (5.19, 71.44)	−0.07 (−0.20, 0.06)
Middle	6,726.03 (928.40, 12,103.05)	1.27 (0.18, 2.28)	16,082.19 (2,212.27, 30,970.98)	1.15 (0.16, 2.21)	−0.69 (−0.84, −0.54)		193,202.31 (26,320.73, 347,938.36)	33.60 (4.60, 60.35)	396,686.72 (54,434.19, 771,740.31)	27.40 (3.77, 53.20)	−1.02 (−1.16, −0.87)
Low-middle	790.15 (103.18, 1,455.04)	0.26 (0.03, 0.48)	2,064.11 (266.44, 4,022.48)	0.28 (0.04, 0.54)	0.11 (0.06, 0.15)		23,564.02 (3,047.98, 43,759.22)	7.06 (0.92, 13.05)	58,398.75 (7,557.90, 113,745.28)	7.30 (0.95, 14.23)	0.06 (0.01, 0.11)
Low	92.80 (11.40, 181.22)	0.08 (0.01, 0.16)	230.66 (28.51, 458.98)	0.09 (0.01, 0.18)	0.08 (−0.01, 0.16)		2,799.25 (343.22, 5,480.19)	2.24 (0.27, 4.38)	6,829.95 (831.06, 13,573.49)	2.34 (0.29, 4.65)	−0.06 (−0.15, 0.03)
Age (years)
25–29	107.49 (15.19, 199.28)	0.05 (0.01, 0.09)	76.62 (10.31, 146.41)	0.03 (0.00, 0.05)	−2.11 (−2.39, −1.84)		6,784.89 (958.84, 12,580.51)	3.08 (0.44, 5.72)	4,828.53 (649.18, 9,221.29)	1.66 (0.22, 3.17)	−2.11 (−2.39, −1.83)
30–34	209.76 (28.68, 392.18)	0.11 (0.02, 0.21)	203.45 (28.01, 402.53)	0.07 (0.01, 0.13)	−2.10 (−2.37, −1.84)		12,156.08 (1,661.88, 22,684.74)	6.39 (0.87, 11.93)	11,807.43 (1,625.27, 23,367.74)	3.95 (0.54, 7.82)	−2.10 (−2.36, −1.84)
35–39	461.78 (59.44, 840.46)	0.27 (0.03, 0.48)	386.97 (51.61, 741.68)	0.14 (0.02, 0.27)	−2.55 (−2.76, −2.33)		24,532.08 (3,156.09, 44,639.22)	14.14 (1.82, 25.74)	20,598.65 (2,748.33, 39,432.43)	7.41 (0.99, 14.19)	−2.54 (−2.76, −2.32)
40–44	796.55 (100.54, 1,436.60)	0.57 (0.07, 1.02)	777.08 (100.55, 1,492.55)	0.31 (0.04, 0.60)	−2.16 (−2.40, −1.92)		38,408.98 (4,844.53, 69,281.31)	27.39 (3.45, 49.41)	37,445.99 (4,844.29, 71,896.02)	15.09 (1.95, 28.98)	−2.17 (−2.41, −1.92)
45–49	1,118.25 (148.38, 2,024.09)	0.98 (0.13, 1.78)	1,528.86 (196.99, 2,977.30)	0.65 (0.08, 1.26)	−1.52 (−1.73, −1.31)		48,329.67 (6,407.90, 87,547.25)	42.47 (5.63, 76.93)	66,102.28 (8,520.55, 128,758.92)	28.05 (3.62, 54.64)	−1.52 (−1.73, −1.31)
50–74	13,481.29 (1,776.54, 24,438.60)	3.43 (0.45, 6.22)	24,502.82 (3,206.28, 46,894.84)	2.91 (0.38, 5.57)	−0.89 (−0.99, −0.78)		383,091.12 (50,478.33, 692,659.38)	97.57 (12.86, 176.42)	678,536.33 (89,969.99, 1,301,811.68)	80.59 (10.69, 154.63)	−0.90 (−0.98, −0.82)
75+	4,679.10 (631.97, 8,744.08)	6.48 (0.87, 12.10)	13,586.92 (1,834.74, 26,110.17)	8.11 (1.10, 15.59)	0.43 (0.31, 0.54)		64,650.03 (8,750.67, 120,993.40)	89.49 (12.11, 167.47)	176,990.18 (23,963.13, 341,317.94)	105.67 (14.31, 203.78)	0.24 (0.12, 0.36)

ASDR, age-standardized death rate; ASDAR, age-standardized DALYs rate; CI, confidence interval; DALYs, disability-adjusted life years; EAPCs, estimated annual percentage changes; GBD, Global Burden of Disease; SDI, socio-demographic index; UI, uncertainty interval.

Regional and national levels

In 2021, China recorded the highest number of female deaths globally attributable to SHS-related TBL, with a total of 27,540.58 cases (95% UI: 3,757.58 to 52,697.38). This marked a 2.6-fold increase from 10,460.73 (95% UI: 1,445.38 to 19,221.21) cases in 1990. In contrast, the number of deaths in the United States decreased from 2,028.78 (95% UI: 228.60 to 3,913.10) cases in 1990 to 1,642.59 (95% UI: 211.87 to 3,277.03) cases in 2021. The ASDR also decreased, from 1.22 (95% UI: 0.14 to 2.35) per 100,000 to 0.52 (95% UI: 0.07 to 1.05) per 100,000. Japan also exhibited a declining trend, with deaths decreasing from 937.08 (95% UI: 128.81 to 1,746.63) cases to 784.61 (95% UI: 98.35 to 1,593.36) cases. Concurrently, the ASDR decreased from 0.98 (95% UI: 0.13 to 1.82) per 100,000 to 0.33 (95% UI: 0.04 to 0.66) per 100,000 (Table S1). With regard to DALYs, a considerable decline in female ASDAR has been observed in a number of high-income countries, including Denmark, Canada, the United States and the United Kingdom. For instance, Denmark witnessed a decline from 56.50 per 100,000 population (95% UI: 5.95 to 116.51) to 15.39 (95% UI: 1.85 to 31.91). Similarly, the United States demonstrated a decrease from 35.50 (95% UI: 4.04 to 68.01) to 13.23 (95% UI: 1.64 to 26.43). Conversely, many low- and middle-income countries, particularly in Asia, have experienced significant increases in the burden of female DALYs, both in absolute numbers and rates. For instance, Indonesia experienced an increase from 16.14 (95% UI: 1.80 to 34.38) to 23.35 (95% UI: 3.13 to 49.13) (Table S2).

In 2021, Chile ranked first among 204 countries and territories in terms of ASDR and ASDAR for TBL related to SHS exposure among women (2.50; 95% UI: 0.34 to 4.80 per 100,000 population and 59.78; 95% UI: 8.19 to 114.91 per 100,000 population, respectively). In contrast, Nigeria demonstrated the lowest ASDR and ASDAR values (0.01; 95% UI: 0.00 to 0.02 per 100,000 population and 0.28; 95% UI: 0.03 to 0.64 per 100,000 population, respectively) (Tables S1,S2 and Figure 1A,1B).

Figure 1.

Descriptive analysis of secondhand smoke exposure-related tracheal, bronchial, and lung cancers in women burden at national levels. (A) The ASR of deaths in 2021. (B) The ASR of DALYs in 2021. ASR, age-standardized rate; DALYs, disability-adjusted life years.

From 1990 to 2021, the changes in ASDR and ASDAR for TBL associated with SHS exposure among women in 204 countries and territories exhibited a polarised trend. The most pronounced increases in EAPC for both ASDR and ASDAR were observed in Lesotho (4.81; 95% CI: 4.23 to 5.39 and 4.81; 95% CI: 4.19 to 5.43), while the most pronounced decrease in EAPC for ASDR was observed in Mexico (−4.61; 95% CI: −4.86 to −4.36), and the most pronounced decrease in EAPC for ASDAR was seen in Denmark (−4.58; 95% CI: −4.87 to −4.30). Over the past few decades, countries demonstrating declines in EAPC for ASDR and ASDAR have been predominantly located in North America, Eastern Europe, Australia, and northern South America, while regions exhibiting positive growth in EAPC have been chiefly concentrated in Africa, West Asia, and Southwest Asia (Tables S1,S2 and Figure 2A,2B).

Figure 2.

Trends in age-standardized deaths rates (A) and DALYs rates (B) from tracheal, bronchial, and lung cancers due to secondhand smoke exposure among women globally, 1990–2021. DALYs, disability-adjusted life years; EAPCs, estimated annual percentage changes.

SDI quintile level

In 2021, high-middle SDI regions accounted for the largest proportion of TBL deaths and DALYs attributable to SHS exposure among women across all five SDI regions, representing approximately one-third of the global total. In high-middle SDI regions, the ASDR and ASDAR per 100,000 population were approximately 1.50 (95% UI: 0.20 to 2.86) and 37.60 (95% UI: 5.19 to 71.44), respectively (Table 1).

From 1990 to 2021, a decline in ASDR was observed in the high SDI and middle SDI regions, with EAPC values of −2.00 (95% CI: −2.18 to −1.82) and −0.69 (95% CI: −0.84 to −0.54), respectively. The remaining three regions demonstrated a gradual escalation. For ASDAR, solely the low-middle region exhibited an upward trend, with an EAPC of 0.06 (95% CI: 0.01 to 0.11), whilst all other regions demonstrated negative growth. The trend of change is most pronounced in regions with high SDI, irrespective of whether the ASDR or ASDAR is under consideration (Table 1).

Age patterns

An analysis of the burden of disease attributable to SHS exposure among women across different age groups revealed a distinct age-stratified trend in disease burden from 1990 to 2021. The burden of mortality was primarily concentrated in the 60–79 years age group, while the burden of DALYs was concentrated in the 50–79 years age group (Figure 3). A decline in deaths was observed among individuals aged 25–39 years (e.g., a decrease from 107.49; 95% UI: 15.19 to 199.28 cases to 76.62; 95% UI: 10.31 to 146.41 cases in the 25–29 years age group), while an increase was evident in all age groups above 40 years. For ASDR, the rate exhibited an increase from 6.48 per 100,000 to 8.11 per 100,000 in the 75 years and older age group, while it demonstrated a decrease in all other age groups.

Figure 3.

(A) Deaths and ASR of deaths, (B) DALYs and ASR of DALYs associated with secondhand smoke exposure-related tracheal, bronchial, and lung cancers in women of different age subgroups, globally, 2021. ASR, age-standardized rate; DALYs, disability-adjusted life years; UI, uncertainty interval.

The burden of DALYs for this disease is consistent with mortality rates, with DALYs increasing across all age groups aged 40 years and above. There has been an increase from 383,091.12 (95% UI: 504,783.33 to 692,659.38) to 678,536.33 (95% UI: 899,699.99 to 1,301,811.68) in the 50–74 years age group. The ASDAR exhibited a parallel trend to that of ASDR, with the exception of the 75+ years age group, where ASDAR demonstrated an increase from 89.49 per 100,000 to 105.67 per 100,000. All other age groups demonstrated a decline, with the EAPC for the 25–49 years age group falling below −1.5 (Table 1).

Correlation analysis

The present study examined the relationship between SDI levels in 21 regions and 204 countries and territories and the ASDR and ASDAR of TBL associated with female SHS exposure.

Firstly, within the 21 GBD regions, areas exhibiting higher SDI values demonstrated higher ASDR associated with female SHS exposure-related TBL, thereby signifying that regions characterised by elevated social development exhibit a heightened disease burden related to female SHS exposure-related TBL (Figure 4). A similar set of patterns was observed in the scatter plots of 204 countries and territories. Nations with higher SDI indices exhibited greater ASDR for female TBL attributable to SHS exposure, thus confirming prior findings. Subsequent analysis of ASDAR for female TBL attributable to SHS exposure revealed that the disease burden increased in a progressive manner alongside rising SDI indices (Figure 5).

Figure 4.

The ASR of deaths and DALYs in relation to SDI in different regions. (A) Deaths. (B) DALYs. The dotted lines represent the different regions labeled in the legend, while the black curves indicate the overall trend. ASR, age-standardized rate; DALYs, disability-adjusted life years; SDI, socio-demographic index.

Figure 5.

The relationship between the SDI and the ASR of deaths and DALYs in countries/territories. (A) Deaths. (B) DALYs. ASR, age-standardized rate; DALYs, disability-adjusted life years; SDI, socio-demographic index.

Frontier analysis of SHS exposure-related TBL

The present study employed frontier analysis to evaluate the health performance of 204 countries and territories regarding female SHS exposure-related DALYs, as measured by GBD data. The analysis quantified each country’s deviation from the health frontier (eff_diff) by comparing actual DALY rates (val) with theoretical optimal values (frontier) at corresponding SDI levels. From Figure 6, it can be observed that among the 15 countries with the highest eff_diff values, China (eff_diff =59.61), Greenland (eff_diff =56.56), and Montenegro (eff_diff =39.39) rank at the top. This indicates that the actual ASDAR in these countries is significantly higher than the theoretical optimal value corresponding to their SDI levels. The majority of these countries have medium to high SDI (0.47–0.91), yet their health performance falls short of its potential optimal level. Among low-SDI countries (SDI <0.5), Somalia (eff_diff =0) and Niger (eff_diff =0.07) exhibit the smallest efficiency gaps, with their actual DALY rates approaching or reaching frontier levels. In contrast, Ethiopia (eff_diff =0.45) and Malawi (eff_diff =0.33) exhibit larger discrepancies. While high-SDI countries such as Monaco (SDI =0.91, eff_diff =34.64) and Canada (SDI =0.87, eff_diff =16.05) demonstrate superior levels of development, they also exhibit considerable disparities in efficiency.

Figure 6.

Frontier analysis of secondhand smoke exposure-related tracheal, bronchial, and lung cancers in women based on DALYs. (A) The effective difference from the frontier for each country or territory by all years (from 1990 to 2021). (B) The effective difference from the frontier for each country or territory by single year (2021 vs. 1990). DALYs, disability-adjusted life years; SDI, socio-demographic index.

Decomposition analysis

A decomposition analysis was conducted in order to examine changes in the ASDR and ASDAR of TBL associated with female SHS exposure from 1990 to 2021.The impact of three determinants—namely, aging, epidemiological shifts, and population growth—on the overall disease burden is the subject of this study. From 1990 to 2021, the global mortality rate from TBL attributable to SHS exposure among women increased. The primary driver of change was population growth (87.42%), while ageing (27.59%) also had a significant impact. The epidemiological improvements (−15%) have been shown to offset the adverse effects of the first two factors to a certain extent. A marginal increase in mortality was observed in regions with high SDI, despite substantial epidemiological progress (−794.17%), primarily attributable to population ageing and growth. Regions exhibiting middle and high SDI levels experienced a significant escalation in mortality, a phenomenon attributable to two interrelated factors: namely, population growth and the deterioration of epidemiological conditions. Conversely, regions exhibiting low-middle and low SDI levels exhibited a predominant influence of population growth (Figure 7A).

Figure 7.

Decomposition analysis of ASR of deaths (A) and DALYs (B) for secondhand smoke exposure-related tracheal, bronchial, and lung cancers in women in the world and SDI regions. ASR, age-standardized rate; DALYs, disability-adjusted life years; SDI, socio-demographic index.

Concurrently, the rise in ASDAR from lung cancer attributable to SHS exposure among women worldwide was predominantly driven by population growth (109.69%) and ageing (27.7%). This decline was partially mitigated by epidemiological improvements, which saw a 37.39% reduction in the burden of disease. The overall ASDAR in high-SDI regions declined, a phenomenon attributable to significant epidemiological improvements (592.29%). Regions with middle and high SDI emerged as the focal point for disease burden growth, with population increase contributing most significantly (63.99%). Although the total burden rose in regions with middle SDI, epidemiological improvements moderated the growth rate. Regions with low-middle and low SDI experienced relatively moderate DALYs growth, still dominated by population increase (Figure 7B).

Prediction

The findings of the present study indicate that from 1990 to 2021, the number of female deaths and DALYs attributable to SHS exposure-related TBL showed an initial increase followed by a decline (Figure 8). Projections indicate that by 2035, the number of female deaths and DALYs attributable to SHS exposure-related TBL will reach approximately 37,645 and 888,641, respectively.

Figure 8.

Projected number of new cases for all female secondhand smoke exposure-related tracheal, bronchial, and lung cancers in 2035. Shaded areas represent 95% uncertainty intervals. (A) Death. (B) DALYs. DALYs, disability-adjusted life years.

Discussion

This study based on continuous data from the GBD 1990–2021, comprehensively assessed the disease burden and trends of TBL cancer caused by SHS exposure among women globally from 1990 to 2021 and projected the global disease burden up to 2035. The findings indicated that the global disease burden of TBL caused by SHS exposure among women has generally declined. Although the overall burden caused by SHS exposure was less significant compared to women’s TBL in general (5), ASDR and ASDAR have decreased. However, the number of global deaths among women due to TBL caused by SHS exposure has increased, underscoring that SHS exposure remains a serious public health issue. Projections suggested that this declining trend will continue over the next three decades. Stratified analyses revealed a heavier disease burden in regions with middle-to-high SDI, with the burden predominantly concentrated among those aged 55–79 years. Additionally, the distribution of the disease burden across GBD regions and countries was uneven. Overall, the findings highlight notable age and regional disparities in the global death toll, DALYs, ASDR and ASDAR among women due to TBL caused by SHS exposure. This underscores the need for targeted interventions and policy priorities in key regions and the importance of increasing screening efforts within specific populations.

The study observed significant downward trends in mortality rates, incidence rates, and DALYs of TBL cancer burden in high-income regions, in 2008, the WHO introduced the MPOWER package of tobacco control measures for the first time in order to implement the WHO Framework Convention on Tobacco Control. Despite the proposal of these measures many years ago, there is considerable variation in their implementation between countries. The United States and Canada are regarded as exemplars of tobacco control practice, having adopted multi-level intervention strategies. These strategies encompass comprehensive bans on smoking in public places, the incorporation of nicotine replacement therapy (NRT) and cessation medications into health insurance coverage, and systematic reduction of the prevalence of tobacco dependence (16). At the heart of these trends lies the pervasive influence of tobacco. Developed regions saw an early peak in smoking habits, triggering a surge in lung cancer cases and deaths (16). Thankfully, the tide turned with the advent of effective tobacco control measures, ushering in a gradual decline. To reduce the projected burden of TBL, targeted smoking cessation initiatives in regions with low tobacco prevalence are imperative. Many low-income and middle-income countries are in the later stages of the tobacco epidemic, where the effects of decades of tobacco consumption are increasingly evident (17,18). Tobacco control measures such as smoking bans, tobacco taxation, graphic warnings, and public health campaigns often come later in low-income and middle-income countries compared to high-income countries (17). China and other populous nations are facing significant challenges in their efforts to combat the tobacco epidemic. The large size of their respective populations results in a disproportionate number of smokers, contributing to some of the highest rates of smoking globally. The key obstacles to tobacco control are as follows: firstly, there is inadequate enforcement of existing tobacco control policies; secondly, there is persistently low tobacco tax rates; and thirdly, there is ongoing interference from the tobacco industry. Furthermore, improving access to healthcare resources is critical in combating this challenge. In highly developed areas, effective public health policies, healthcare advancements, and lifestyle modifications reduce the overall disease burden, particularly for preventable conditions. Studies indicated a significant reduction in mortality rates following the widespread adoption of low-dose computed tomography (LDCT) screening in the United States (19,20). In Japan, the prognosis for TBL cancer was better than other developed nations, which may be attributed to a higher prevalence of specific subtypes that respond well to targeted therapies (21,22). By combining robust tobacco control policies with improved healthcare access and early detection strategies, the global burden of TBL cancer can be mitigated more effectively in the coming years.

The global burden of TBL cancer associated with SHS exposure in women has consistently been highest in the 50–80 years age group. The health impact of SHS accumulates over time, leading to a higher disease burden in older age groups. Aging lungs are more susceptible to damage and infections, exacerbating the impact of SHS exposure (23). Many SHS-related conditions, such as lung cancer, typically manifest in later life (24). While tobacco control measures have advanced, sustained efforts to eliminate SHS exposure and enhance preventive healthcare for older women remain crucial (25). The guidelines of the National Comprehensive Cancer Network (NCCN) recommended starting lung cancer screening at age 50 years for high-risk populations. According to the Chinese Medical Association’s recommendation, start screening should at 45 years (26). Research indicated that females have a higher risk than males of developing lung cancer with specific driver mutations, particularly involving the epidermal growth factor receptor (EGFR) (27,28). Lung cancer patients with EGFR mutations tend to be diagnosed at an older age compared to those without such mutations (29,30). Estrogen plays a significant role in the development of lung cancer, with overexpression of estrogen receptors contributing to sex-specific differences (31). Estrogen may be associated with signaling changes with age, especially post-menopause, and impact on lung cancer incidence and progression (32). Among Japanese individuals who never smoked, an exceptional pattern was noted. Females were diagnosed with lung cancer at a later age compared to males (33). This trend was consistent among both Japanese individuals living in Japan and the United States (33). This finding suggests potential genetic, environmental, or cultural factors influencing the timing of lung cancer diagnosis in this subgroup. Efforts to address SHS exposure and understand its nuanced effects across different populations and age groups remain vital in reducing the global burden of TBL cancer.

From 1990 to 2021, the ASDR and ASDAR for SHS-related TBL among women continuously decline. Predictions indicated that this downward trend will likely continue through 2035. This trend reflects global public health advancements and targeted efforts to mitigate SHS exposure in high-risk populations, particularly women. Over the past few decades, many high-income countries have implemented strict environmental regulations, leading to significant reductions in lung cancer incidence. However, Zhou et al. recently reported that global lung cancer cases are projected to grow by 86.2%, from 2.48 million in 2022 to 4.62 million by 2050 (34). One of possible reasons is that by 2036, the proportion of people aged 55+ years is expected to rise significantly, particularly in middle- and high-income countries (35). In certain underdeveloped regions, the disease burden of TBL shows an upward trend. Long-term heterogeneous trends are observed across different genders and age groups, particularly among middle-aged and elderly populations and women (36). While the United States Preventive Services Task Force (USPSTF) guidelines for lung cancer screening consider smoking history and age as key risk factors, the magnitude of lung cancer risk varies significantly among eligible individuals due to unaccounted risk factors. By not considering these additional risk factors, the guidelines may underestimate the risk in certain high-risk groups. Individuals with heavy SHS exposure might be overlooked in screening programs, despite having a significantly elevated risk. While LDCT remains the cornerstone of lung cancer screening, liquid biopsies and artificial intelligence (AI) are being developed as complementary tools to enhance screening accuracy and efficiency (37-39). Moving forward, addressing the challenges of an aging population and the limitations of current screening guidelines will be critical to mitigating the global burden of TBL and lung cancer.

This study provided a comprehensive analysis of the global disease burden of TBL cancer caused by SHS exposure among women from 1990 to 2021 and projects trends up to 2035. The study utilized data from GBD spanning over three decades, which allowed for a robust evaluation of long-term trends in TBL burden. By narrowing the focus to women exposed to SHS, our study highlighted a vulnerable population often overshadowed in broader lung cancer research. Despite a general decline in TBL burden, the rising number of deaths due to SHS exposure remains a critical public health concern.

There are some limitations in this study. First, the study’s reliance on GBD data introduces potential variability in accuracy and reliability due to differences in the quality and consistency of health registry data across countries. Second, the aggregated nature of the data may obscure year-to-year variations or localized events, such as economic downturns, natural disasters, or public health crises, which could significantly influence TBL burden within specific contexts. Future studies should aim to address these issues by incorporating more granular data, improving data collection and reporting systems, and accounting for social and environmental determinants that influence health outcomes.

Conclusions

This study revealed a declining trend in the global burden of TBL cancer caused by SHS exposure among women, with reductions in ASDR and ASDAR from 1990 to 2021 and projections indicating further declines by 2035. However, the rising number of deaths underscores that SHS remains a significant public health issue, particularly in middle-to-high SDI regions and among women aged 55–79 years.

Supplementary

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Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.