Cigarettes and cancer

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p1t1o
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Cigarettes and cancer

Postby p1t1o » Thu May 23, 2013 7:22 pm UTC

Hi all,
I know at least the basics around how drug substances work in the body, genetics, how cancer is caused and how cigarettes are harmful, but my question is:

Does smoking a whole bunch of cigarettes in a short space of time have more potential to cause cancer than the same number smoked over a longer period?
Say, the difference between smoking 20 a day for 1 year against 4 a day for 5 years?
Or perhaps 20 and 4 over 5 and 25 years?

screen317
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Re: Cigarettes and cancer

Postby screen317 » Thu May 23, 2013 7:59 pm UTC

On one hand, the same exposure over a longer period of time may impact the cilia in the bronchi less; however, I can't comment on the effect on mutations which result in cancers. I'll try to find some studies that have looked at this specifically.

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Re: Cigarettes and cancer

Postby ahammel » Thu May 23, 2013 8:24 pm UTC

I believe that researchers usually collect data on "totally number of cigarettes smoked", which makes sense given how cancer works. I would think that 20 a day for 1 year increases your risk of lung cancer by about the same ammount as 4 a day for 5 years.
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Re: Cigarettes and cancer

Postby Izawwlgood » Thu May 23, 2013 8:29 pm UTC

I'd also be curious to hear what the research has indicated. My sense is that the body can tolerate persistent but low level stress better than high insult, but then, persistent low level stress can obviously lead to cancer as well.

So yeah, I'm not sure what's worse; spreading the stress over the course of multiple years, or increasing the stress over a shorter time scale.
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Re: Cigarettes and cancer

Postby ahammel » Thu May 23, 2013 8:34 pm UTC

Izawwlgood wrote:I'd also be curious to hear what the research has indicated. My sense is that the body can tolerate persistent but low level stress better than high insult, but then, persistent low level stress can obviously lead to cancer as well.

So yeah, I'm not sure what's worse; spreading the stress over the course of multiple years, or increasing the stress over a shorter time scale.
Isn't total somatic mutation load the most important factor? I wouldn't think it matters that much for lifetime risk whether it's spread out or not.

I suppose smoking 20 cigs a day could do bad things to one's immune system, which would increase cancer risk.
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Izawwlgood
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Re: Cigarettes and cancer

Postby Izawwlgood » Thu May 23, 2013 8:42 pm UTC

I'm honestly not sure. For example, individuals can tolerate low level radiation over long periods of time due to DNA repair mechanisms, but cannot tolerate single massive doses. The DNA damage repair lab downstairs that looks at double strand breaks says that singular events slow mitosis, whereas multiple events stop it. So, yeah, I'm honestly not sure.
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Re: Cigarettes and cancer

Postby Angua » Thu May 23, 2013 8:44 pm UTC

I'm not sure, however I can tell you that when assessing risk, physicians (in the UK at least) define it in terms of 'packyears' which is defined as 20cigs/day/for one year. So if you smoke 10 a day for 20 years you have the same number of packyears as someone smoking 20/day for 5 years, or 40/day for 2.5 years.

I guess you could probably look up the term pack-years to find out where it originated from to get the data. I'm too tired to do it tonight and will be too busy tomorrow.
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Re: Cigarettes and cancer

Postby qetzal » Fri May 24, 2013 3:37 pm UTC

I found a really interesting study on exactly this point. Here's the key conclusion:

Lubin & Caporaso wrote:Our results show that the EOR/pack-year increases with intensity for subjects who smoke ≤20 cigarettes per day and decreases with intensity for subjects who smoke >20 cigarettes per day. At lower smoking intensities, the data support an “exposure enhancement” effect, such that for equal total exposure, the EOR/pack-year of smoking increases with intensity. At higher smoking intensities, data support a “reduced potency” or “wasted exposure” effect, such that for equal total exposure, smoking at a lower intensity for longer duration is more deleterious than smoking at a higher intensity for shorter duration. It is important to note that these patterns reflect effects of intensity and not lung cancer risk. For example, the inverse intensity effect implies that an increase in smoking intensity decreases risk per pack-year and does not imply a decrease in the overall risk of lung cancer, which depends on both total pack-years of exposure and smoking intensity.


(EOR = excess odds ratio, i.e. the increased chance of getting cancer relative to a non-smoker.)

If this paper is correct, smoking ~ 1 pack/day for X years is worse than smoking 0.5 pack/day for 2X years, but also worse than smoking 2 packs/day for 0.5X years! Of course, this is just one paper. I don't have the time/inclination to survey the whole literature, but a PubMed search for related citations would be a good place to start if anyone's interested to dig further.


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