Large differences exist worldwide in the scale of harm caused by secondhand smoke on nonsmokers, according to study results published in JAMA.

For their calculations, researchers used data from Our World in Data, which provided numbers from various world regions for smokers and individuals who died from secondhand smoke-related causes. The analysis included data from 1990 through 2016 from the following regions: North America, Latin America, and the Caribbean; Europe and Central Asia; the Middle East and North Africa; sub-Saharan Africa, South Asia, and East Asia; and the Pacific.

The researchers used this data in an equation formulated specifically for calculating the number of smokers associated with the death of one nonsmoker and the number of pack-years associated. To account for the delay of harm caused by secondhand smoke, the researchers incorporated lead-time delay of 0, 2, 10, and 20 years into their calculations and used a mean of 24 years of smoking as an additional variable.

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The secondhand smoke index (SHSI), the number of smokers associated with the death of one nonsmoker, was calculated for each region included in the data set. Through this analysis the researchers determined that the overall deaths from secondhand smoke exposure had decreased from 946,041 in 1990 to 848,702 in 2006. After that point, the number increased gradually to about 883,930 by 2016. Regionally, this increase was associated mostly with deaths that occurred in South Asia, East Asia, and the Pacific. The average number of cigarettes per day decreased across the entire period, from 25 to 18, and the number of associated pack-years increased between 1990 and 2016 from 751.9 to 1255.9.

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Across the world there was a gradual, favorable increase in the number of smokers associated with the death of one nonsmoker, from 31.3 in 1990 to 52.3 in 2016. The researchers attributed part of this change to anti-tobacco initiatives and smoking bans across the world. In North America, for instance, the SHSI was favorable compared with regions that offer nonsmokers little protection from secondhand smoke. Considering this disparity among regions, the SHSI could be an important tool to determine which regions need additional measures to decrease the harm caused by secondhand smoke.

The researchers suggested that legislators might use these and similar data as a foundation for implementing new anti-tobacco policies. They did acknowledge several limitations to the study, including variance in data quality and variation of delay in onset of secondhand smoke-related diseases, both of which they aimed to account for in their analysis.


Yousuf H, Hofstra M, Tijssen J, et al. Estimated worldwide mortality attributed to secondhand tobacco smoke exposure, 1990-2016. JAMA Netw Open. 2020;3(3):e201177. doi:10.1001/jamanetworkopen.2020.1177