Wednesday, August 19, 2009

Heart Attack and Stroke Risks from Smokeless Tobacco Use: Next to Nil

The International Agency for Research on Cancer (IARC) is a component of the World Health Organization with a mission “to identify the causes of cancer so that preventive measures may be adopted and the burden of disease and associated suffering reduced.” It is therefore not surprising that IARC staff have played a prominent role in exaggerating the cancer risks of smokeless tobacco use. The IARC anti- smokeless tobacco campaign has been led by Paolo Boffetta.

Boffetta, a cancer epidemiologist, departed from his field of expertise to complete (with co-author Kurt Straif) a review of the risks for heart attack and stroke among smokeless tobacco users in the U.S. and Sweden. The analysis has just been published by the British Medical Journal.

Boffetta reported that the summary relative risk (RR) for heart attack among smokeless tobacco users was 0.99, with a 95% confidence interval (CI) of 0.89 to 1.10 (For a discussion on how to interpret RRs and CIs, see my recent post). For stroke, Boffetta reported a minimal increase in risk (RR = 1.19) that was not statistically significant (CI = 0.97 – 1.47). Thus, the main finding in this study is that smokeless tobacco users have no excess risk of heart attack or stroke.

Given the importance of that conclusion, why did the researchers (in their BMJ abstract) and subsequent media coverage ignore it, focusing instead on fatal heart attack/stroke, one of two subgroups? It is because smokeless tobacco users had very small elevations in risk for the fatal events. For fatal heart attack the RR among smokeless users was 1.13 (CI = 1.06 – 1.21), and the RR for fatal stroke was 1.40 (CI = 1.28 – 1.54). Boffetta was unable to demonstrate that the excess risks were related to how much or how long smokeless tobacco had been consumed, two important characteristics that would have strengthened the validity of the findings.

There is a serious omission in this study. Boffetta divided all heart attacks and strokes into two subgroups, fatal and non-fatal. Boffetta found that smokeless users had no significant risk for all heart attacks and strokes but had elevated risks for fatal cases. It logically follows that smokeless users probably had LOWER risks for NON-FATAL heart attacks and strokes. But Boffetta provided no information about these subgroups, and the reason is obvious: it wouldn’t add to the health hysteria.

Here is the take-home message for smokeless tobacco users: You do not have elevated risks for heart attack and stroke. Although your risk for heart attack and stroke is the same as that of non-users of tobacco, there is a slight increased chance that, if one occurs, it could be fatal. This may be due to the effects of nicotine on the circulatory system, or it could be due to some other undiscovered factor that is associated with smokeless use. As Boffetta acknowledged, “the magnitude of the excess risk is small.”

In the article’s introduction, Boffetta wrote that smokeless tobacco “products have been proposed as an alternative to cigarettes and other smoking products under the claim of a smaller, or negligible, risk to health.” This study adds to the scientific evidence that, compared with cigarettes, the risks from smokeless tobacco are indeed vastly “smaller, or negligible.”


Chris Snowdon said...

This may be due to the effects of nicotine on the circulatory system, or it could be due to some other undiscovered factor that is associated with smokeless use.

Or I could be due, as it usually is, to the inevitability of chance. What a shame that Mr Boffetta never takes his own advice.

Just come across your excellent blog today and am grateful to you for pointing me at that study, and showing how the old sub-divide/cherry pick trick is at work once again.

Clive Bates said...

Hey Brad! I've only just seen your amazing blog... really great stuff. Nothing like the truth... Sadly, my new employer has had me take mine off line.

Best wishes

Clive (Bates)