Systematic Reviews
Copyright ©The Author(s) 2020. Published by Baishideng Publishing Group Inc. All rights reserved.
World J Meta-Anal. Jun 28, 2020; 8(3): 245-264
Published online Jun 28, 2020. doi: 10.13105/wjma.v8.i3.245
Exclusive cigar smoking in the United States and smoking-related diseases: A systematic review
Peter N Lee, Janette S Hamling, Alison J Thornton
Peter N Lee, Department of Statistics, P.N. Lee Statistics and Computing Ltd., Sutton, Surrey SM2 5DA, United Kingdom
Janette S Hamling, Department of Statistics, RoeLee Statistics Ltd., Sutton SM2 5DA, United Kingdom
Alison J Thornton, Independent Consultant, Okehampton, Devon EX20 1SG, United Kingdom
Author contributions: Lee PN designed the study; Hamling JS carried out the searches and the analyses; Hamling JS and Thornton AJ entered the data on the databases; Lee PN, Hamling JS and Thornton AJ checked the data entered and discussed changes needed; Lee PN and Hamling JS wrote the paper; all authors read and approved the final manuscript.
Supported by the JT International SA, Assignment Schedule, No. 14.
Conflict-of-interest statement: No conflict of interests.
PRISMA 2009 Checklist statement: The manuscript was revised according to the PRISMA 2009 Checklist.
Open-Access: This article is an open-access article that was selected by an in-house editor and fully peer-reviewed by external reviewers. It is distributed in accordance with the Creative Commons Attribution NonCommercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/
Corresponding author: Peter N Lee, MA, Director, Senior Statistician, Consultant Medical Statistician, Department of Statistics, P.N. Lee Statistics and Computing Ltd., 17 Cedar Road, Sutton, Surrey SM2 5DA, United Kingdom. peterlee@pnlee.co.uk
Received: February 13, 2020
Peer-review started: February 13, 2020
First decision: February 26, 2020
Revised: May 15, 2020
Accepted: June 10, 2020
Article in press: June 10, 2020
Published online: June 28, 2020
Processing time: 144 Days and 19.9 Hours
ARTICLE HIGHLIGHTS
Research background

Many reviews have studied the relationship of smoking to lung cancer, chronic obstructive pulmonary disease (COPD), heart disease and stroke, but the effects on these diseases of cigar smoking, particularly exclusive cigar smoking, have rarely been considered.

Research motivation

As the United States is a country with a large population and a relatively high percentage of cigar smokers, we felt that insight into the effects of exclusive cigar smoking could usefully be gained from studies conducted there.

Research objectives

To carry out a systematic review of the relationship of exclusive cigar smoking to the four main smoking-related diseases in studies conducted in the United States.

Research methods

Literature searches were conducted to identify studies in the United States that reported risk of lung cancer, COPD, heart-disease, stroke and/or overall circulatory disease comparing cigar smokers who had never smoked other tobacco products with those who had never smoked any tobacco. For each study identified as providing relevant results, data were recorded on study characteristics and on the appropriate relative risks (RRs) and 95%CIs relating to overall current, former and ever exclusive cigar use, and, for current smokers, by daily cigar consumption. RRs for a given smoking group and disease were combined using fixed-effect and random-effects meta-analyses.

Research results

Data were available on lung cancer from 11 studies, on COPD from four studies and on heart disease, stroke and circulatory disease from 10 studies. As RRs tended to be heterogeneous, random-effects estimates are given below. For current smoking overall RR estimates were 2.98 (95%CI: 2.08 to 4.26, based on n = 6 estimates) for lung cancer, 1.44 (1.16 to 1.77, n = 4) for COPD, 1.11 (1.04 to 1.19, n = 6) for ischaemic heart disease, 1.02 (0.92 to 1.13, n = 5) for stroke and 1.10 (1.05 to 1.16, n = 3) for overall circulatory disease. These RRs are much lower than those reported for the United States for exclusive cigarette smokers; 11.68 for lung cancer, 4.56 for COPD and at least 1.70, depending on age, for ischaemic heart disease. Even for heavy cigar smoking, RRs are generally lower than for overall cigarette smoking. RRs for former and for ever smoking were also much lower than for cigarette smoking.

Research conclusions

Although our analyses were based on relatively few studies, some conducted some time ago, the results clearly show that exclusive cigar smoking is associated with an increased risk of lung cancer, though much less than is the case for exclusive cigarette smoking. For COPD and ischaemic heart disease the association is weaker, and also less than for cigarette smoking. No previous study has clarified the effects of exclusive cigarette smoking so clearly. Future research could extend results on exclusive cigar smoking to countries other than the United States, and compare risks of cigar smoking with those of using other nicotine products.

Research perspectives

While our results show that exclusive cigar smoking is associated with risks of smoking-related diseases that are much lower than those associated with cigarettes smoking, little of the evidence comes from studies conducted in this millenium. Further large prospective studies are needed to collect more up-to-date results, and to clarify how risk varies by type of cigar smoked.