Cigarette smoke is the most common toxin to cause disease and one of the leading causes of heart disease. Understanding just how cigarette smoke damages the heart, and particularly DNA in cells in and around the heart, has been the focus of much research.

One experimental method of finding where cigarettes smoke is causing harm, and specifically where it is producing harmful DNA adducts (large, disruptive molecules that muck up DNA), is to add a radioactive "tracer" to smoke and then do special tests on the "smoker" to find where the radioactivity collects. In rats, smoke goes first to the lungs and heart, with a lesser amount gathering in the liver. After several weeks of exposure to smoke, the level of DNA adducts in the rats' hearts is twice as high as the level in their lungs, and several times higher than the levels in their windpipes, throats, livers or bladders.²²

Autopsy studies on human smokers confirm that the DNA adducts in the heart are higher than in the lungs.^23,24

In addition to pushing DNA adducts into heart cells, cigarettes smoke also increases oxidative damage to the DNA and other components of heart cells. Cells in the heart possess many natural defenses against the damage caused in the process of converting oxygen to energy, but they lack one of these detoxifying defenses, namely cytochrome P450. This may explain why heart cells are particularly vulnerable to the DNA damage of cigarette smoke.^25,26

Excessive oxidative stress in the mitochondria, the cells' energy powerhouses, damages the DNA of those mitochondria, and this too has been linked to the neurodegenerative diseases of aging.³³