Socioeconomic Inequality in Respiratory Health in the US From 1959 to 2018

Abstract

Importance: Air quality has improved and smoking rates have declined over the past half-century in the US. It is unknown whether such secular improvements, and other policies, have helped close socioeconomic gaps in respiratory health.

Objective: To describe long-term trends in socioeconomic disparities in respiratory disease prevalence, pulmonary symptoms, and pulmonary function.

Design, setting, and participants: This repeated cross-sectional analysis of the nationally representative National Health and Nutrition Examination Surveys (NHANES) and predecessor surveys, conducted from 1959 to 2018. included 160 495 participants aged 6 to 74 years.

Exposures: Family income quintile defined using year-specific thresholds; educational attainment.

Main outcomes and measures: Trends in socioeconomic disparities in prevalence of current/former smoking among adults aged 25 to 74 years; 3 respiratory symptoms (dyspnea on exertion, cough, and wheezing) among adults aged 40 to 74 years; asthma stratified by age (6-11, 12-17, and 18-74 years); chronic obstructive pulmonary disease ([COPD] adults aged 40-74 years); and 3 measures of pulmonary function (forced expiratory volume in 1 second [FEV1], forced vital capacity [FVC], and FEV1/FVC<0.70) among adults aged 24 to 74 years.

Results: Our sample included 160 495 individuals surveyed between 1959 and 2018: 27 948 children aged 6 to 11 years; 26 956 children aged 12 to 17 years; and 105 591 adults aged 18 to 74 years. Income- and education-based disparities in smoking prevalence widened from 1971 to 2018. Socioeconomic disparities in respiratory symptoms persisted or worsened from 1959 to 2018. For instance, from 1971 to 1975, 44.5% of those in the lowest income quintile reported dyspnea on exertion vs 26.4% of those in the highest quintile, whereas from 2017 to 2018 the corresponding proportions were 48.3% and 27.9%. Disparities in cough and wheezing rose over time. Asthma prevalence rose for all children after 1980, but more sharply among poorer children. Income-based disparities in diagnosed COPD also widened over time, from 4.5 percentage points (age- and sex-adjusted) in 1971 to 11.3 percentage points from 2013 to 2018. Socioeconomic disparities in FEV1 and FVC also increased. For instance, from 1971 to 1975, the age- and height-adjusted FEV1 of men in the lowest income quintile was 203.6 mL lower than men in the highest quintile, a difference that widened to 248.5 mL from 2007 to 2012 (95% CI, -328.0 to -169.0). However, disparities in rates of FEV1/FVC lower than 0.70 changed little.

Conclusions and relevance: Socioeconomic disparities in pulmonary health persisted and potentially worsened over the past 6 decades, suggesting that the benefits of improved air quality and smoking reductions have not been equally distributed. Socioeconomic position may function as an independent determinant of pulmonary health.

Figure 1.. Prevalence of Respiratory Symptoms Among Adults Aged 40 to 74 Years by Family Income Quintile, 1959 to 2018

The dashed lines indicate a major change in the survey question. Data for each survey is presented at the middle year of the survey period (or the year following the midpoint for surveys with an even number of years). Quintile 1 = lowest quintile; quintile 5 = highest quintile. A, In the National Health Examination Survey I ([NHANES]1959-1962; presented at 1961), the question refers to shortness of breath with stairs, with 4 affirmative responses based on frequency and severity; we classified individuals as having dyspnea on exertion if they responded affirmatively regardless of frequency or severity. From NHANES I (1971-1975; presented at 1973) onward, the question refers to dyspnea with “hurrying on the level or walking up a slight hill,” and there are no frequency or severity responses (n = 48 969). B, In NHANES I (1971-1975; presented in 1973), the question refers to “trouble with recurring persistent cough attacks,” but from NHANES III (1988-1994; presented at 1991) onward it refers to “usually cough on most days for 3 consecutive months or more during the year.” Cough was not ascertained in the continuous NHANES after 2012 (n = 30 295). C, In NHANES I (1971-1975; presented in 1973), the question refers to ever having “wheezy or whistling sounds in your chest.” In NHANES II (1976-1980; presented at 1978), it asks whether “during the past 12 months, not counting colds or the flu, have you frequently had trouble with… wheezing.” From NHANES III (1988-1994; presented at 1991) and onward it refers to “wheezing or whistling” in the chest in the past 12 months. Wheezing was not ascertained in the continuous NHANES after 2012 (n = 39 537).

Figure 2.. Respiratory Disease Prevalence by Family Income Quintile, 1962 to 2018

The dashed lines indicate major changes in survey wording. Data for each survey is presented at the middle year of the survey period (or the year following the midpoint for surveys with an even number of years). Quintile 1 = lowest quintile; quintile 5 = highest quintile. A, For the National Health Examination Survey II ([NHANES] 1962-1965; presented at 1964) the question asks whether a child “ever had asthma,” and for NHANES I (1971-1975; presented at 1973), to whether a child has “ever been treated” for asthma. From NHANES II (1976-1980; presented at 1978) onward, the question refers to a physician (or other health professional for NHANES 1999-2018) ever having said the child had asthma, and if the child still had asthma. For these surveys, we only included children “still” with asthma as having asthma (n = 25 972). B, For NHES III (1966-1970; presented at 1968), the question refers to ever having asthma, but for NHANES I onward, the question asks whether a clinician ever said that the child had asthma, and if so, whether he or she still had it. For these surveys, we only included children still with asthma as having asthma (n = 24 379). C, In 1999-2000, NHANES lacked a question on whether asthma was still present among adults, and was not presented herein. Definition of asthma included only those still with asthma for all other survey years (n = 86 802). D, Defined as ever being told by a physician (or other health professional for 1999-2018) that the patient had emphysema or chronic bronchitis (n = 50 772).