Cigarette smoke damages DNA within minutes, selenium, green tea reduce the risk

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Preventing the genetic damage smoking can cause

Within minutes of being inhaled into the lungs cigarette smoke causes genetic mutations linked to lung cancer, according to a new study in the Chemical Research in Toxicology.

Stephen S. Hecht at the University of Minnesota in Minneapolis and colleagues added an isotope-labeled [D(10)]phenanthrene - a type of polycyclic aromatic hydrocarbon or PAH to cigarettes and then let 12 volunteers smoke the cigarettes.  The isotope-labeled chemical is used for the researchers to track its fate in the human body.

Hecht found smokers developed a maximum serum level of a toxic substance known as [D(10)]r-1,t-2,3,c-4-tetrahydroxy-1,2,3,4-tetrahydrophenanthrene ([D(10)]PheT), which is known to damage DNA, just 15 to 30 minutes after cigarette smoke was inhaled. 

PAHs are known harmful substances found in tobacco smoke.  Toxic matagenic and carcinogenic PAH diol epoxides can be derived from PAHS, which are responsible for most cases of lung cancer. 

The study demonstrates harm is caused much faster than early thought.

The researchers concluded "the results clearly demonstrate immediate negative health consequences of smoking, which should serve as a major warning to anyone contemplating initiating tobacco use."

So how can cigarette smokers, or people exposed to second hand smoke,  lower the risk of lung cancer?

Taking selenium supplements may help.

A study reported this year in the FASEB Journal suggests taking dietary selenium supplements may help inhibit the formation of DNA adducts resulting from exposure to cigarette smoke.

Joshua Blake Martin and colleagues of University of Kentucky in Lexington, KY fortified three diets with 0.15, 0.5 or 2.0 mg/kg selenium in the form of sodium selenite and gave three groups of female mice half of whom were exposed to cigarette smoke six hours a day for five months. The other half were used as controls.

The researchers found mice exposed to smoke were more likely to develop tumors and mice fed the diet with 2.0 ppm selenium were less likely to develop tumors than those on the diet with 0.5 ppm Se.

Exposure to smoke boosted the growth of tumors and selenium could not stop the growth of lung can liver cancers.

The researchers concluded high levels of dietary selenium may inhibit the development of lung cancer.

Green tea may also help reduce smoke-induced lung cancer risk 

Hakim I.A. and colleagues from University of Arizona in Tucson, AZ reported in the Aug 2008 issue of Journal of Nutrition that drinking green tea may help decrease DNA damage in smokers who are GSTM1 positive. 

In the study, researchers assigned smokers to drink decaffeinated green tea, or black or water, measured urinary 8-hydroxydeoxyguanosine or 8-OHdG and found drinking four cups of tea per day was correlated with a significant decrease in urinary 8-OHdG among the green tea drinkers. 

8-OHdG is believed to be one of the most abundant DNA lesions resulting from oxidative stress and is a biomarker of the oxidative DNA damage and repair.

David Liu and editing by Aimee Keenan-Greene

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