9 In Asia, the majority of ST studies have been carried out in India where both the habits and the negative outcomes (mainly oral cancers) are most prevalent, and strong dose dependent associations have been found. The US states with highest ST use (West Virginia) do not have high rates of oral cancers. Sweden has a low rate of oral and pharyngeal cancers despite high ST use. The ecological analyses available to date from Western countries have been inconclusive. Levels of the most powerful carcinogens-tobacco-specific N-nitrosamines (TSNAs)-vary widely in different ST products 6 and recent production trends may have reduced these levels. ST is not homogeneous 1 there are significant differences in composition and production.
5 Nevertheless, the negative health effects of ST use have been questioned. 4 An IARC monograph in 1984 similarly concluded that snuff use causes cancer. 4 ST use can be addictive, leading to oral leukoplakias (oral mucosal lesions), gingival recession, and may play a contributory role in the development of cardiovascular disease, peripheral vascular disease, hypertension, peptic ulcers, and fetal morbidity and mortality”. A US Surgeon General report in 1986 concluded that “the use of snuff can cause cancer in humans” and “the excess risk of cancer of the cheek and gum may reach nearly 50-fold among long term snuff users”. Major reviews in the mid 1980s concluded that ST use has substantial negative health implications. Chewing is practised in different ways: the main ingredients are usually areca nut (betel), betel leaf, lime and tobacco. In developing countries, tobacco is mostly chewed with other ingredients. Chewing tobacco is predominantly used in the USA and snuff (snus) in Sweden. 1 The main types of ST in Western countries are chewing tobacco and oral snuff. It has been in use for as long as other forms of tobacco consumption and its use has increased. Smokeless tobacco (ST) is tobacco consumed orally, not smoked. Further rigorous studies with adequate sample sizes are required, especially for cardiovascular disease. Most recent studies from the US and Scandinavia are not statistically significant, but moderate positive associations cannot be ruled out due to lack of power. Few studies have adequately considered the non-cancer health effects of ST use.Ĭonclusions: Chewing betel quid and tobacco is associated with a substantial risk of oral cancers in India. Studies from other regions and of other cancer types were not consistent.
Studies in India showed a substantial risk of oral or oropharyngeal cancers associated with chewing betel quid and tobacco. Studies were often not designed to investigate ST use, and many also had major methodological limitations including poor control for cigarette smoking and imprecise measurements of exposure.
Many of the studies lacked sufficient power to estimate precise risks, mainly due to the small number of ST users. Results: A narrative review was carried out. Selection, extraction and quality assessments were carried out by one or two independent reviewers. Data extraction covered control of confounding, selection of cases and controls, sample size, clear definitions and measurements of the health outcome, and ST use. Analytical observational studies of ST use (cohorts, case-control, cross sectional studies) with a sample size of ⩾500 were included if they reported on one or more of the following outcomes (all cause mortality, oral and pharyngeal cancers, other cancers, cardiovascular diseases, dental diseases, pregnancy outcomes, surgical outcomes). Methods: Several electronic databases were searched, supplemented by screening reference lists, smoking related websites, and contacting experts. A systematic review was therefore carried out to summarise these risks. Background: It is believed that health risks associated with smokeless tobacco (ST) use are lower than those with cigarette smoking.