Influence of dose and cessation of kiraiku, cigarettes and alcohol use on the risk of developing oral leukoplakia.

Data from a previously-reported study of oral leukoplakia-associated risk factors in a Kenyan population were further analyzed to determine the influence of dose and cessation. Specifically, risk analysis was made with respect to kiraiku (a traditional Kenyan type of home-made, hand-rolled tobacco product), cigarettes, and commercial beer. The relative risk (RR) of oral leukoplakia among those who smoked > 10 cigarettes was 14.7, as compared to 6.7 among those who smoked < or = 10 cigarettes. With regard to duration, the RR increased from 7.4 in those who had smoked for < or = 15 years to 10.8 in those who had smoked for > or = 30 years. Among those who had quit smoking, RR value was significant only in ex-kiraiku smokers (RR = 4.9, 95% confidence interval (CI) = 2.3-20.4) and was dependent on both the duration of smoking and duration since quitting. For commercial beer, the RR was significant in consumers of > 10 bottles per drinking day (RR = 4.2, 95% CI = 1.0-3.9) and in those whose who drank for > or = 5 days per month (RR = 3.8, 95% CI = 1.0-15.1). Duration of beer consumption did not significantly influence the RR of oral leukoplakia. The RR in ex-beer consumers was not statistically significant. These findings suggest a dose-dependent association between oral leukoplakia and the use of tobacco and alcohol, in which the number of cigarettes smoked, the quantity of beer consumed, and the frequency of consumption were more important than the duration of use of these products. Furthermore, while oral leukoplakia due to cigarette smoking may regress completely, those due to kiraiku may persist for more than 10 years after cessation of these habits.