Adding to the exhaustive list of societal ills supposedly caused by smokers (e.g., heart disease, diabetes, J. Geils Band), is this article published in the British Medical Journal (1).
To be quite honest, as far as studies of second hand smoke (SHS) go, this is quite good. But then again, Hillary Clinton looks good next to a bloated and naked Alan Schatzberg.
One thing this study included that most studies of SHS didn't was an actual objective measure of nicotine exposure (cotinine). Typically, study participants are given questionnaires in which they are asked to remember past exposure to SHS during the earlier decades of life. That's not what I would call "scientific."
First the results: "Participants who did not smoke, use nicotine products, or have salivary cotinine concentrations of 14.1 ng/ml or more were divided into four equal size groups on the basis of cotinine concentrations. Compared with the lowest fourth of cotinine concentration (0.0-0.1 ng/ml) the odds ratios (95% confidence intervals) for cognitive impairment in the second (0.2-0.3 ng/ml), third (0.4-0.7 ng/ml), and highest fourths (0.8-13.5 ng/ml) were 1.08 (0.78 to 1.48), 1.13 (0.81 to 1.56), and 1.44 (1.07 to 1.94; P for trend 0.02), after adjustment for a wide range of established risk factors for cognitive impairment."
While the authors did control for known risk factors for cognitive impairment, they didn't control for known factors associated with elevated cotinine (other than SHS).
Once nicotine is in the body, between 70-80% is converted to the metabolite cotinine by the P450 liver enzyme CYP2A6. The remainder is converted into nicotine-N-oxide, nornicotine, and norcotinite. All of which are excreted in urine. Cotinine usually sticks around in your system for 20-25 hours after exposure to nicotine. What its presence does not indicate, is how one came in contact with nicotine.
Therefore, "Cotinine is a marker of exposure to many risk factors other than tobacco smoke. These correlations could confound studies of the health effects of smoking, especially passive smoking." (2).
Here are some of the known factors that are associated with increased levels of cotinine in nonsmokers: low education, low SES, high alcohol consumption, low fruit or vegetable consumption, high fried food consumption, and low breakfast cereal consumption. These are just the factors significant at the p<0.001 level and doesn't include factors at levels 0.01 and 0.05.
Lastly, some people, due to genetic variation, have low CYP2A6 activity, which reduces the rate of nicotine metabolism. These people are more likely to be nonsmokers (3).
Since none of the above-mentioned factors were taken into consideration, what the BMJ study is actually examining is the association between cotinine level and cognitive impairment, not SHS exposure per se.
I'm still not convinced by this apparent association either. The highest level of cotinine was 13.5ng/ml. In this study (2), the amount of cotinine is actual smokers ranged from 80.9ng/ml to 389.4 ng/ml, while nonsmokes ranged from 0.6 ng/ml to 0.8 ng/ml.
If nicotine exposure in small amounts can lead to cognitive impairments (as the study suggests), then smokers should be developing dementia at rates similar to people with Down syndrome (4). Since less than a quarter of the population are smokers (5, there are more ex-smokers than smokers now), a decline in the rate of dementia should be on the horizon.
That's about as likely to happen as electing an Arab US president (Obama doesn't count, he's only half Arab).
I know people love to hate smokers and like to pretend SHS exposes people to nearly equal amounts of toxic chemicals and increased health risks as actual smokers (read this idiot's rant, 6), but that's just not the reality of the situation (7, 8).
Besides, SHS is so 1990's. Today, we are faced with a new threat to our health: Third-Hand Smoke (9). I shit you not. Go ahead, read the article while I have a smoke...
Did you read it? Are you afraid for your child's health and safety? Well, I hope you are, because that was the entire point. I'm actually feeling guilty for blowing smoke in the faces of all those babies at that Romanian orphanage. Excuse me while light-up another one...
David J Llewellyn, Iain A Lang, Kenneth M Langa, Felix Naughton, & Fiona E Matthews (2009). Exposure to secondhand smoke and cognitive impairment in non-smokers: national cross sectional study with cotinine measurement BMJ