Electronic cigarettes are potentially harmful to DNA

This is confirmed by a recent study carried out on rodents and human tissue: Electronic Cigarettes Are Potentially Harmful to DNA

According to the authors, they produce damage to the repair mechanisms of the lungs and bladder.
A group of New York University researchers, led by Moon-shong Tang, report potential DNA damage from electronic cigarette smoke. This product releases nicotine without burning tobacco, thus avoiding the carcinogenic by-products of curing and burning tobacco.

Electronic cigarettes are marketed as a less harmful alternative to smoking tobacco. The Moon-shong Tang team found that mice exposed to these cigarettes had higher levels of DNA damage to the heart, lungs and bladder than control mice exposed to filtered air. At the same time, DNA repairing activity was reduced, as was the level of certain proteins in the lungs involved in DNA repair.

These effects were also seen in cultured human lung and bladder cells exposed to nicotine and nitrosamine ketone (NNK), a carcinogenic derivative of nicotine. Cultured human cells exposed to these substances showed higher rates of mutation and tumour transformation than control cells. The results suggest that nitrosation (the process of converting an organic compound into nitrous derivatives) of nicotine can occur in certain human and mouse tissues, and that the resulting products are further metabolized into compounds that damage DNA. Therefore, although electronic cigarettes have fewer carcinogens than tobacco smoke, those who use them may have a higher risk of developing lung and bladder cancer and heart disease than nonsmokers, according to the authors.
The study, entitled E-cigarette smoke damages DNA and reduces repair activity in mouse lung, heart, and bladder as well as in human lung and bladder cells, has been published in Proceedings of the National Academy of Sciences.