But that has changed drastically. By the survey period 2017-18, current and former smoking rates among the wealthiest dropped by nearly half to 34 percent — while rates among the poorest inched up to 57.9 percent.

Though smoking is an acquired habit, lower-income people may be more likely to use tobacco to cope with the stresses of poverty, Dr. Gaffney said. Tobacco advertising often targets low-income communities, and there is a higher density of tobacco stores in poor neighborhoods, according to the authors of a commentary accompanying the study. Poor people may also have more limited access to smoking cessation programs and replacement therapies, they said.

“We’re increasingly thinking of tobacco dependence as a disease,” said Dr. Sarath Raju, an assistant professor of pulmonary and critical care medicine at Johns Hopkins University and one of the authors of the commentary. “Individual responsibility is important, but without appropriate treatment or access to treatment to help you quit, that’s a challenge.”

Among children, asthma rates increased in all income groups after 1980, but they rose more sharply among children from poorer households. There was little difference in asthma rates in young children aged 6 to 11 before 1980, which stood at 3 percent to 4 percent. But by 2017-18, rates among the poor increased to 14.8 percent, compared with 6.8 percent among children from the highest income families. (A similar pattern emerged among adults; statistical adjustments for smoking only slightly reduced the differences.)

Among low-income adults, rates of chronic obstructive pulmonary disease, an inflammatory lung disease, have long been higher than among wealthier individuals. But rates have increased, widening the gap, with prevalence among the poorest Americans increasing to 16.3 percent from 10.4 percent, even as the rate remained stable, at 4.4 percent, among the wealthiest.

Between 1959 and 2019, poorer and less-educated adults consistently reported more troubling respiratory symptoms, like labored breathing, than wealthier, more educated people. For some symptoms, like having a problem cough, the gap between the rich and poor widened over time.

Wheezing rates fell for the highest income and most educated groups, but they remained stable in the poor, least educated groups, the study found.