Health Risks of Kretek Cigarettes: A Systematic Review

INTRODUCTION: The objective of this study is review the evidence on the health risks associated with smoking kretek cigarettes compared with not smoking or smoking regular cigarettes. METHODS: We conducted a systematic literature search in five electronic databases: EMBASE (Ovid), ASSIA, PubMed and Scopus. Since kretek use is largely restricted to Indonesia, we identified additional studies using an online search for grey literature and studies in Indonesian journals and the National Library of Indonesia. We included relevant search terms in English (“kretek” and “clove cigarettes”) and Bahasa (“rokok” and “merokok”). We selected studies which compared any health outcome between smokers of kretek cigarettes and non-smokers or smokers of regular cigarettes. We included studies in any smokers compared to non-smokers in Indonesia, since most Indonesian smokers use kretek, but analysed these separately. Study data were extracted by a single reviewer and checked by two reviewers. Methodological quality was assessed using the Newcastle-Ottawa scale. RESULTS: We identified 32 studies, all from Indonesia. There were 31 cross-sectional studies and one case control study. This systematic review identified a relatively limited number of studies, and most of these were of poor quality as assessed by the Newcastle Ottawa score. They were generally cross-sectional, small and lacking justification for sample size, had high potential for selection bias because of lack of data on non-respondents or those lost to follow up, and missing information about the statistical analysis. Fourteen studies looked specifically at kretek exposure and eighteen looked at any type of cigarette exposure but were conducted in Indonesia are therefore likely to predominantly reflect kretek exposure. Kretek were found to be associated with oral cancer, cardiovascular disease, chronic health disease, myocardial infarction, asthma, and oral diseases. CONCLUSIONS: Although existing studies are of poor quality, kretek are likely to be at least as harmful as regular cigarettes.