Abstract
AimThis systematic review and meta-analysis aimed to critically appraised data from comparable studies leading to quantitative assessment of any independent association between use of oral smokeless tobacco in any form, of betel quid without tobacco and of areca nut with incidence of oral cancer in South Asia and the Pacific.MethodsStudies (case control and/or cohort) were identified by searching Pub Med, CINAHL and Cochrane databases through June 2013 using the keywords oral cancer: chewing tobacco; smokeless tobacco; betel quid; betel quid without tobacco; areca nut; Asia, the Pacific and the reference lists of retrieved articles. A random effects model was used to compute adjusted summary ORRE for the main effect of these habits along with their corresponding 95% confidence intervals. To quantify the impact of between-study heterogeneity on adjusted main-effect summary ORRE, Higgins' H and I2 statistics along with their 95% uncertainty intervals were used. Funnel plots and Egger's test were used to evaluate publication bias.ResultsMeta-analysis of fifteen case–control studies (4,553 cases; 8,632 controls) and four cohort studies (15,342) which met our inclusion criteria showed that chewing tobacco is significantly and independently associated with an increased risk of squamous-cell carcinoma of the oral cavity (adjusted main-effect summary for case- control studies ORRE = 7.46; 95% CI = 5.86–9.50, P<0.001), (adjusted main-effect summary for cohort studies RR = 5.48; 95% CI = 2.56–11.71, P<0.001). Furthermore, meta-analysis of fifteen case control studies (4,648 cases; 7,847 controls) has shown betel quid without tobacco to have an independent positive association with oral cancer, with OR = 2.82 (95% CI = 2.35–3.40, P<0.001). This is presumably due to the carcinogenicity of areca nut. There was no significant publication bias.ConclusionThere is convincing evidence that smokeless (aka chewing) tobacco, often used as a component of betel quid, and betel quid without tobacco, are both strong and independent risk factors for oral cancer in these populations. However, studies with better separation of the types of tobacco and the ways in which it is used, and studies with sufficient power to quantify dose-response relationships are still needed.
Highlights
There are more than seventy species of tobacco, where Nicotiana tabacum is the chief commercial crop
It was not known in Pacific communities before European contact [4] and was introduced to Papua New Guinea by Malay traders [5,6]
Betel quid (BQ), or ‘‘paan’’ as it is known in the Indian language Hindi [12] is one of the four most commonly used psychoactive substances, used by 600 million people around the world [8,12,13]
Summary
There are more than seventy species of tobacco, where Nicotiana tabacum is the chief commercial crop This was first introduced into South Asia in the 1600s as a product to be smoked and gradually became popular in many different smokeless forms [1,2,3]. ‘BQ’/‘paan’ is normally defined as ‘a substance, or mixture of substances, placed in the mouth, usually wrapped in betel leaf (derived from the Piper Betel vine) with at least one of two basic ingredients: i.e. with/without tobacco and sliced fresh or dried areca nut (Areca catechu). The latter is an indispensable ingredient of BQ. The use of lime lowers the intraoral pH, enhancing the stimulant effect of the nicotine in tobacco [17]
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