Tea drinking is associated with decreased number of cancer and heart diseases. This is probably explained with the antioxidant effect of polyphenols that tea contains. A randomized research was conducted to find out the effect of high consumption (4 cups a day) of decaffeinated black or green tea upon the oxidative DNA damage among smokers within a 4-months period.
In the framework of the study, researchers measured the content of 8-hydroxy-deoxyguanosine (8-OhdG) in the urine of smokers. In general, 143 heavy smokers at the age of 18-79 were randomized to drink either black or green tea or water. The level of catechins in urine and plasma, and also urine 8-OhdG were measured monthly. 133 smokers completed the experiment successfully. Multiple regression models were used to determine the effect of the intervention. The group of smokers who were drinking green tea revealed much higher level of catechins in blood and urine as compared with the rest two groups. The content of 8-OhdG in urine significantly decreased (by 31 per cent) in the green tea group after 4 months of drinking green tea. No change in urinary 8-OhdG was registered among smokers who were drinking black tea within the same period. The results of the study reveal that regular drinking of green tea protects smokers from oxidative damages and reduce cancer risk or other diseases caused by free radicals that appear as a result of smoking.