We know smoking leads to life threatening diseases. The estimate today is that it causes 5 million deaths worldwide every year.

More studies are now revealing what happens in a smoker's genes. In one recent episode, we told you about a study that found a smoker's tumor cells had thirty–three thousand mutations. That's approximately one mutation for every fifteen cigarettes smoked.

Now, a new study of over twelve hundred people has identified three hundred twenty genes that are affected by smoking. This is the largest study of its kind ever reported.

It looked at smokers and their non–smoking relatives and at the gene expression of their white blood cells.

Remember: gene expression is the business end of genes – where proteins are produced. They do the work needed to provide the structure and machinery that run our cells. Alter that process, and the result can be disease, cancer or death!

The study found expression changes not only in single genes needed for healthy cell function but also in large networks of genes.

There was a profound negative influence on genes involved in immune function, as well as those involved in cell death, inflammatory processes and other aspects of metabolism that could lead to disease.

For example, of twenty–nine genes responsible for our immune response, twenty–three showed depressed levels in smokers. Of the so called "Killer cells," which are part of our immune surveillance system, all eleven genes showed a negative correlation with smoking!

These results could explain why smoking can lead to a wide variety of cancers – such as kidney, colon, bladder, and pancreatic. According to the study's authors, never before has such a clear link between smoking and gene expression been made.

The somewhat heartening news is that, after stopping smoking, many of the gene expression changes may be reversed. But for some, the changes may be permanent.