Smoker's saliva a 'cocktail of chemicals'

LONDON (Reuters) - Smoking destroys protective molecules in saliva and transforms it into a dangerous cocktail of chemicals that increases the risk of mouth cancer, scientists say.

"Cigarette smoke is not only damaging on its own, it can turn the body against itself," said Dr Rafi Nagler, of the Technion-Israel Institute of Technology in Haifa, Israel.

Saliva contains antioxidants, molecules that normally protect the body against cancer, but Nagler and his colleagues have discovered that cigarette smoke destroys the molecules and turns saliva into a dangerous compound.

"Our study shows that once exposed to cigarette smoke, our normally healthy saliva not only loses its beneficial qualities but it turns traitor and actually aids in destroying the cells of the mouth and oral cavity," he added.

In research reported in the British Journal of Cancer on Wednesday, Nagler and his team studied the impact of cigarette smoke on cancerous cells in the laboratory.

Half of the cells were exposed to saliva exposed to cigarette smoke and the other half just to the smoke. Cells exposed to the saliva mixture had more damage and it increased along with the time of exposure.

"Most people will find it very shocking that the mixture of saliva and smoke is actually more lethal to cells in the mouth than cigarette smoke alone," Nagler added in a statement.

Smoking and drinking are the leading causes of head and neck or oral cancers, which includes cancer of the lip, mouth, tongue, gums, larynx and pharynx. Nearly 400,000 new cases of the illness are diagnosed worldwide each year with the majority in developing countries. The five-year survival rates are less than 50 percent.

Nagler and his colleagues believe the research could open up new avenues to develop better treatments to prevent oral cancer.

"This insight into how mouth cancer can develop offers more reasons for smokers to try and quit," said Jean King, of Cancer Research UK, which publishes the journal. "People know the link with lung cancer and this research adds compelling evidence about the damage smoking can do to the mouth."

Here is a finding of fault with the methodology. A very serious fault.

Editor—According to Enstrom and Kabat's figures the greater had been a man's cigarette consumption in 1959 the less likely, it seems, was the death of his wife from coronary heart disease.1 However, an age bias existed in those women at the outset. In 1959 their mean age decreased with spousal smoking, such that the wives of men smoking 40 a day were a mean four years younger than wives of men smoking one to 19 a day, probably as a consequence of early death of smoking husbands of similarly aged wives (table 3 on bmj.com).

During the study period mortality from coronary heart disease fell by about 15% every four years.2 The "passive" smokers were therefore predominantly from later cohorts for whom, age for age, mortality from coronary heart disease had fallen significantly in comparison to controls. The same argument applies to never smoking husbands of smoking women who had an average age four to five years lower than controls (table 2 on bmj.com). Adjusting for age alone will not remove this interaction of age and time of observation.

Moreover, the Cox proportional hazard model is critically dependent on assumed proportionality between two survival curves at all points following entry to the study.3 Mortality from coronary heart disease increases almost exponentially for most of adult life and the mortality curves of risk groups for coronary heart disease differ not only in scale but also in doubling time. As such their survival curves cannot be proportional, yet this was not tested.

The effectiveness of age adjustment in this study is questionable, the year of observation should have been taken into account, and the statistical method is potentially unsound. The biological implausibility of the trend in relative risk may well be an expression of systematic bias in the method.

Eugene Milne, deputy medical director

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