# Low Dose Smoking

**URL:** <https://boards.straightdope.com/t/low-dose-smoking/397>\
**Category:** Cecil's Columns/Staff Reports\
**Created:** [December 23, 1999, 1:52am UTC](https://boards.straightdope.com/t/low-dose-smoking/397 "1999-12-23T01:52:00Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![ElvisP](https://avatars.discourse-cdn.com/v4/letter/e/5f9b8f/32.png) [@ElvisP](https://boards.straightdope.com/u/ElvisP)\
**Post date:** [December 23, 1999, 1:52am UTC](https://boards.straightdope.com/t/low-dose-smoking/397/1 "1999-12-23T01:52:00Z")

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\<\< In February of 1995 (Yes, I know that was a long time ago, but I am a very slow typist) Cecil wrote

\<\<Although the data is unclear, many believe the relationship between smoking  
and disease is linear: the more you smoke the greater your risk, but any  
smoking presents some risk\>

Actually the effect is non-linear, with larger than expected effects occurring at low doses. There has been a lot of discussion of this non-linearity in medical journals, because breathing secondhand smoke is like being a smoker of low amounts of cigarettes.

An article entitled “Environmental Tobacco Smoke Exposure and Ischaemic Heart Disease: an Evaluation of the Evidence” in the October 18 1997 issue of the British Medical Journal says

\<\<Risk of smoking one cigarette per day  
Figure 2 shows the dose-response relation in each of the five studies of smoking and ischaemic heart disease (age standardised to age 65). The risk of ischaemic heart disease increases continuously with daily cigarette  
consumption, but in all five studies linear extrapolation of the regression  
line back to zero dose (no cigarettes per day) does not yield the expected  
relative risk estimate of 1.0. The estimates from the five individual studies  
of the risk at low dose are consistent with each other, and the weighted  
average relative risk at one cigarette per day (defining risk in non-smokers  
as 1.0) was 1.39 (1.18 to 1.64; P\<0.001). At 20 cigarettes per day this risk  
was 1.78\>\>

In other words, smoking one cigarette per day raises the risk of heart  
attack by 39%.

The entire article can be found at:  
[http://www.bmj.com/cgi/content/full/315/7114/973](http://www.bmj.com/cgi/content/full/315/7114/973)

The reason for the very large effect at small doses is that the effect on  
clotting abnormalities has a very non-linear behavior. Very low doses are almost as potent as large doses in doing this. The following is from the Harvard Study in the May 20 1997 issue of CIRCULATION (a scientific journal of the American Heart Association)

\<\<Several potential mechanisms have been identified through which passive  
smoking may increase the risk of coronary heart disease. These include  
carboxyhemoglobinemia, increased platelet aggregation, damage to the arterial  
endothelium, and reduced HDL cholesterol. In one experiment, the sensitivity  
of platelets to the antiaggregetory action of exogenous prostacyclin (PG2)  
was compared in smokers and non-smokers before and after they sat in a room  
for 20 minutes where cigarettes had been smoked just before the experimental  
subjects had entered. No change in platelet sensitivity was detected among  
smokers; however a significant change occurred among the platelets of  
non-smokers such that their sensitivity to the anti-aggregatory action of PG2  
was not discernably different from the smokers\>\>

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**Author:** ![Bletchley](https://avatars.discourse-cdn.com/v4/letter/b/7bcc69/32.png) [@Bletchley](https://boards.straightdope.com/u/Bletchley)\
**Post date:** [December 23, 1999, 5:03am UTC](https://boards.straightdope.com/t/low-dose-smoking/397/2 "1999-12-23T05:03:00Z")

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You make an excellent point about recent advances in our understanding of cardiovascular disease. At one time we felt that the narrowing of the arteries due to atherosclerosis gradually progresses until the vessel becomes occluded. We have now learned that there are stable and non stable atherosclerotic lesions. The non stable lesions are characterised by inflammation and give rise to the tiny blood clots that we now feel are responsible for cardiovascular events. Of course smoking is associated with inflammation to the inner lining of the blood vessels, known as the intima. So are other conditions, such as chronic low grade infections. Remarkably, curing such infections has been shown to decrease the incidence of cardiovascular events. These studies were retrospective and involve the antibiotics doxycycline and ciprofloxacin. Prospective studies would of course be more convincing.

Anyway, the issue you bring up about the risk being associated with the formation of tiny blood clots is right on the bloody cutting edge of our advancing medical knowledge.

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**Author:** ![yamo](https://avatars.discourse-cdn.com/v4/letter/y/ecae2f/32.png) [@yamo](https://boards.straightdope.com/u/yamo)\
**Post date:** [January 4, 2000, 9:46pm UTC](https://boards.straightdope.com/t/low-dose-smoking/397/3 "2000-01-04T21:46:00Z")

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So Brush twice and floss once per day! Do your heart a favor! I wouldn’t mind getting older if it didn’t mean getting worse.

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**Author:** ![JillGat](https://avatars.discourse-cdn.com/v4/letter/j/9fc29f/32.png) [@JillGat](https://boards.straightdope.com/u/JillGat)\
**Post date:** [January 5, 2000, 4:13am UTC](https://boards.straightdope.com/t/low-dose-smoking/397/4 "2000-01-05T04:13:00Z")

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Which column are you discussing?