Exclusive cigar smoking in the United States and smoking-related diseases: A systematic review

BACKGROUND Little information has been published on the risks of cigar smoking. Since 1990 cigar smoking has become more prevalent in the United States.AIM To summarise the evidence from the United States relating exclusive cigar smoking to risk of the major smoking-related diseases.METHODS Literature searches detected studies carried out in the United States which estimated the risk of lung cancer, chronic obstructive pulmonary disease（COPD）, heart disease, stroke or overall circulatory disease in exclusive cigar smokers as compared to those who had never smoked any tobacco product. Papers were identified from reviews and detailed searches on MEDLINE. For each study, data were extracted onto a study database and a linked relative risk database. Relative risks and 95%CIs were extracted, or estimated, relating to current, former or ever exclusive cigar smokers, and meta-analysed using standard methods. Sensitivity analyses were conducted including or excluding results from studies that did not quite fit the full selection criteria（for example, a paper presenting combined results from five studies, where 86% of the population were in the United States）.RESULTS The literature searches identified 17 relevant publications for lung cancer, four for COPD and 12 for heart disease, stroke and circulatory disease. These related to 11 studies for lung cancer, to four studies for COPD and to eight studies for heartdisease, stroke or overall circulatory disease. As some studies provided results for more than one disease, the total number of studies considered was 13, with results from four of these used in sensitivity analyses. There was evidence of significant heterogeneity in some of the meta-analyses so the random-effects estimates are summarized below. As the results from the sensitivity analyses were generally very similar to those from the main analyses, and involved more data, only the sensitivity results are summarized below. For lung cancer, relative risks（95%CI） for current, former and ever smokers were respectively, 2.98（2.08 to 4.26）, 1.61（1.23 to 2.09）, and 2.22（1.79 to 2.74） based on 6, 4 and 10 individual study estimates. For COPD, the corresponding estimates were 1.44（1.16 to 1.77）, 0.47（0.02 to 9.88）, and 0.86（0.48 to 1.54） based on 4, 2 and 2 estimates. For ischaemic heart disease（IHD） the estimates were 1.11（1.04 to 1.19）, 1.26（1.03 to 1.53） and 1.15（1.08 to 1.23） based on 6, 3 and 4 estimates, while for stroke they were 1.02（0.92 to 1.13）, 1.08（0.85 to 1.38）, and 1.11（0.95 to 1.31） based on 5, 3 and 4 estimates. For overall circulatory disease they were 1.10（1.05 to 1.16）, 1.11（0.84 to 1.46）, and 1.15（1.06 to 1.26） based on 3, 3 and 4 estimates.CONCLUSION Exclusive cigar smoking is associated with an increased risk of lung cancer, and less so with COPD and IHD. The increases are lower than for cigarettes.