The science behind 6 million deaths a year

Perhaps no medical or scientific research has the potential to save as many lives as does research on pathology of smoking. Almost half a million Americans die every year from smoking, and 6 million smokers die from cancer, heart attacks, lung disease and other illness worldwide. New research by a Harvard group led Dr. Roby Joehanes suggests that methylation damage to more than third of all genes in smokers may be the culprit in long-term damage caused by smoking. The research is published in the journal Circulation: Cardiovascular Genetics (of the American Heart Association): http://circgenetics.ahajournals.org/content/early/2016/09/14/CIRCGENETICS.116.001506

The Harvard team found that smoking causes methylation of DNA bases, which in turn usually silences expression of associated genes. The addition of the methyl group (-CH3) to the cytosine inhibits transcription of the genetic code, which is necessary for synthesis of important functional and structural proteins in the cell.

One surprising result of the study is that methylation of the DNA was observed in smokers across vast stretches of the genome, including about one third of all functional genes encoded by the human DNA. The second surprising result of the study was that the methylation changes can remain for up to 5 years after smoking cession, including changes in genomic regions implicated in leukemia and other diseases. It is worth noting that enzymes called methyltransferases can remove methyl groups from the DNA, in effect repairing the epigenetic damage caused by the downstream effects of smoking. However, the long persistence of some of the DNA methylation presents a possibility that these epigenetic modifications can either be markers for serious, life-threatening diseases associated with smoking, or that they may be directly implicated in the molecular pathology of cancer, heart and lung disease.