P. Jayalekshmi of the Regional Cancer Centre (RCC) here, who led the study on bidi-induced lung, oral, laryngeal and hypopharyngeal cancer, said lung cancer risk among former bidi smokers was higher than in those who never smoked bidis.
Separate studies on the impact of bidi smoking on lung and oral cancers, and cancers of larynx and hypopharynx in close to 70,000 men between the age group of 30-84 in Karunagappally in Kollam district shows that bidi is among the most harmful smoking products.
"The risk of cancer affecting the cheek (buccal) and lips (labial) showed a nearly four-fold increase in the cohort study covering 66,277 men."
"Excessive use of bidis significantly increased the risk associated with cancer of the gum and mouth," Jayalekshmi said.
The mainstream smoke of bidi contains a much higher concentration of carcinogenic hydrocarbons. Bidi smokers also are found to be taking five puffs per minute, compared to two puffs by cigarette smokers in the same time, the study showed.
The cohort study on bidi and lung cancer, covering a total of 65,829 men, found that bidi smokers had a 3.9-fold increase in lung cancer incidence, when compared to those who never smoked bidis.
The study showed that tongue cancer risk increased significantly among men who smoked bidis for 30 years or longer, and among men who started bidi smoking at 18 years or younger.
Yet another cohort study conducted on 69,943 men, again in the 30-84 age group in Karunagappally, shows a significant relationship between bidi smoking and cancers affecting the larynx and hypopharynx.
The results show that those with a history of bidi smoking for more than 30 years have a higher risk of laryngeal cancers. Smokers who puff more than 15 bidis a day are at increased risk of hypopharyngeal cancer.
Figures with Regional Cancer Centre here show that 821 and 863 males registered as lung and oral cancer patients, respectively, during 2011-12 alone.
Another 392 patients registered for care of hypopharyngeal and laryngeal cancers during the same period.
As many as 1.6 million males in Kerala smoke bidis and the Karunagappally studies have also reiterated the common knowledge that bidi smoking is more widespread among those with lower levels of education and family income.
Bidi smokers in Kerala spend nearly Rs.140 monthly on this habit.
The study, however, provides encouragement to those seeking to kick the bidi habit -- the risk of lung cancer is lower in former smokers than current smokers, it showed.
The lung cancer risk was found to decrease significantly among those who had stopped bidi smoking for 10 years or longer, when compared to current bidi smokers.