NCPA - National Center for Policy Analysis


February 24, 2006

Nicotine has many effects including a semi-permanent change in the way the nerves it stimulates talk to each other. The result is that those nerves are uncomfortable without it, and the owners of those nerves become addicted to smoking, says the European Respiratory Journal (ERJ).

Just how many cigarettes an addict needs seems to vary from person to person, but the reason for addiction is genetics -- specifically the enzyme CYP2A6, says ERJ:

  • It is part of the family of toxin-destroying enzymes known as the cytochrome P450s, and one of its jobs is to convert nicotine into a less harmful chemical called continine that can then be excreted.
  • However, the gene that encodes CYP2A6 comes in three varieties that result in a different form of the enzyme, and, on top of that, some people lack the gene altogether.

A study that looked at 200 regular smokers over the age of 50 to see if the particular varieties of CYP2A6 could be correlated with their smoking habits showed that there was, in fact, a connection. According to researchers:

  • Those with two copies of the most common form of the gene (one copy inherited from each parent) smoked most, those with rarer forms smoked less and those completely without the enzyme smoked least.
  • That, paradoxically, is because the most common form of the enzyme is also the most effective at detoxifying nicotine, while an absence of CYP2A6 means that the drug must be detoxified by other, slower routes.
  • In people with effective enzymes, nicotine vanishes rapidly, so they need another cigarette sooner; if the enzyme is less effective, fewer cigarettes are needed to keep the nicotine level up.

Furthermore, this means that what natural selection has favored as healthy may end up killing you faster, says ERJ.

Source: Editorial, "Smoking out the truth," Economist, January 28, 2006; based upon: Hidetoshi Nakamura et al, "Limitation of cigarette consumption by CYP2A6*4, *7 and *9 polymorphisms," European Respiratory Journal, February 2006.

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