Published online Jun 28, 2020. doi: 10.13105/wjma.v8.i3.245
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
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.
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.
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.
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.
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.
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.
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.