I just came across an interesting article reporting on new evidence suggesting that eating peppers substantially reduces the risk of getting Parkinson's disease. It mentioned, in passing, that it is well established that smoking anti-correlates with getting Parkinson's.
The observation that smokers have a lower risk for PD has been "consistently reported in more than 60 epidemiological studies," Honglei Chen, MD, PhD, from the National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina, who wasn't involved in the study, told Medscape Medical News.
The link between smoking and peppers is that both tobacco and vegetable peppers are in the same vegetable family (Solanaceae) and that pepper contain small amounts of nicotine.
The information about peppers is more relevant to me than the information about smoking, since smoking has enough negative effects to make it quite unlikely I will start doing it—although I have played with the idea of trying one of the smoking substitutes, such as a nicotine patch or an eCigarette, to see if I like the effects. But the information about smoking is more interesting, precisely because the fact that I was not aware of it is evidence of a problem with the mechanisms by which information reaching me gets filtered.
Assuming that the quote from Chen correctly reports the evidence—a quick google suggests it does, and that the effect is substantial—it is surely relevant to the question of whether people ought to smoke, a positive effect, possibly a substantial one, to set against the well established negative health effects. So why has it not been widely reported, at least widely enough so that I would have heard of it? Why does it only appear as a passing comment in a news story about something else?
My guess is that it is for the same reason that the evidence that moderate alcohol consumption is good for you is not widely known, a point I discussed here about a year ago. It is widely, and I think correctly, believed that smoking is bad for you. Hence publicizing evidence against that belief, evidence that in at least one important respect smoking is good for you, amounts to supporting the bad guys, which very few people, whether scientists or journalists, want to do. The result is a sort of informal and unofficial censorship, a filtering of the information that reaches the public to make the case for whatever the conventional view is look stronger than it is.
In a previous post I expressed my skepticism about popular claims on the magnitude of the negative effect of second hand smoke. While I think those claims are bogus, my guess is that second hand smoke does have negative effects, since there is good evidence that smoking does. But ...
For a long time, opponents of nuclear testing argued that the resulting increase in background radiation increased the rate of cancer and birth defects, on the grounds that high levels of radiation were known to do so. The implicit assumption was that the negative effect was proportional to the dosage, that if a large amount of radiation had a substantial effect, a small amount had a proportionally smaller effect. As I understand the evidence, that assumption turned out not to be true, the standard counterexample being Denver. Because it is about a mile above sea level, the background level of cosmic radiation is higher than most other places people live, but rates of cancer and birth defects are not correspondingly elevated, indeed may not be elevated at all.
That suggests that human biology can deal with low levels of radiation, has problems only with high levels. Suppose that turns out to be true of the effect of tobacco smoke as well. From the same article:
"A few studies suggest that secondhand smoke might be associated with a reduced risk of PD, so that prompted us to look at another source of a relatively small amount of nicotine — foods in the same plant family as tobacco," [Dr. Searles Nielsen] added.
If it turns out that secondhand smoke does reduce the risk of Parkinson's and does not cause cancer, heart attacks, or other adverse effects associated with smoking, secondhand smoke might, aside from the unpleasant smell, be good for you. If so, even if the evidence turns out to be reasonably good, it may be a long time before you find out.