All of the statistics on smoking I have ever seen are just stats related to the population as a whole and do not establish a purely causal relationship between smoking and negative health outcomes.
I believe, and from my experience, smoking is not a randomly distributed activity throughout the population - smoking is more heavily concentrated among poorer populations and people with certain personality traits are more likely to become smokers.
So, what are the most highly regarded scientific studies on the subject?
More specifically, what exactly did they control for? Did they control for personality attributes, for example - or did they just control for gender, weight, socio economic status etc.?
There’s no causal connection made so far. There is an incredibly strong correlation between smoking and a variety of health problems. It is clearly seen how smoking damages many types of cells and affects the metabolism, there’s just no clear cut evidence that tar or nicotine or anything else in the smoke makes a cell turn cancerous. However it is clearly setting the stage, and sending a limo and rolling out the red carpet for whatever it is that finally makes a cell go cancerous.
I remember being told that smoking can not be proven “scientifically” to cause cancer in humans, because in order to do that you would have to set up a study and control group and force the study group to smoke and the control group not to, (ideally giving the control group fake cigarettes so even they don’t know they’re not smoking,) and studying over several decades, and that is impractical and unethical. Clearly if that was the only standard for these kinds of questions we would never be able to prove that anything causes anything.
The studies in the 50s that showed the correlation between lung cancer and smoking were case-control studies in which a lack of confounding factors is is harder to prove, but is both easier and more ethical to do.
There are also cohort studies where confounding factors are consciously eliminated through the selection of cohorts (but are susceptible to confounding factors not specifically controlled for).
I think self selection, in other words smokers choose to be smokers, makes it difficult for these studies to achieve anything other than high correlation.
That’s not true. For one, they’ve done smoke inhalation studies with rats, and shown that making them smoke results in the sorts of ailments that plague human smokers as well.
To answer the OP’s question broadly, the way to establish causality is to look for evidence that matches a causal explanation. If you see a correlation between A and B, then the three obvious theories are
A causes B
B causes A
Some other thing, C, causes both A and B.
Causality running the other way is the easiest to disprove. If, for example, lung cancer caused people to smoke, then you’d see more people begin to smoke near when they started getting lung cancer, and you probably wouldn’t see people who smoked for 20 years, then stopped, having higher rates of cancer 10 years later. So, that theory doesn’t match the evidence we have.
Some third factor causing both increased disease and a tendency to smoke is harder to rule out, but by no means impossible. Say you think there’s a genetic component. Well, you go find a bunch of identical twins, some of who smoke and some who don’t, and you’ve ruled out genetic differences in the results. Say you think that poverty causes both (it’s clearly correlated with both smoking and poor health). Then you go find a bunch of rich smokers and non-smokers and see if they still have different rates of disease. And so on.
The other thing you do to show causality is to theorize a mechanism, and see if the mechanism works in isolation from other factors. Like, if I wanted to prove that higher temperatures cause more ice cream sales, then I might hypothesize that the mechanism is that people who are hot desire cold things. Then you take some people and put them in rooms of various temperatures and offer them a choice between hot and cold things.
If you take a bunch of lung cell cultures and expose them to cigarette smoke and they get cancerous (or at least you see the type of damage that can lead to cancer, then there’s your mechanism. Sure, there might be more complicated interactions in actual lungs, but you’ve shown that there is a plausible mechanism by which one causes the other, and you’ve done it in a way that removes all the complicated factors like culture and genetics and behavior.
I saw in the OP concerns about self-selection, but something we don’t worry so much about now as compared to the past was 2nd hand smoke.
Even if people weren’t always smokers in the past (though a large portion of the population was), virtually everybody, at least in the US, was exposed to tobacco smoke on a regular basis.
I don’t know which studies, but you can certainly find studies showing that a lot of the diseases associated with direct smoking are found to a lesser degree in people exposed to second hand smoke. And the amount of exposure is correlated with disease risk. For example, non-smokers married to smokers. Or in the workplace.
That’s about as close to a direct link between smoke inhalation and disease as it’s possible to have.
I’ve been participating in a longitudinal study on smoking that started when we were 11-14 years old. We’re all 46-50 now. Apparently there have already been deaths among participants. Smoking-related deaths are among those who smoked early in life and had parents who smoked. Deaths among non-smokers have been from accidents, mainly, with some from AIDS. There’s probably been a cancer death among the non-smokers, but the cancer deaths among smokers outweigh the non-smokers cancer deaths by something overwhelming, like 20 to 1, and that is even allowing for the fact that when the study started, no one knew there would be an event like AIDS to add unusual cancer and pneumonia deaths to the mix.
As people get older, the non-smokers will catch up with poor health events, because aging does that, but the study will probably end with a group of old non-smokers. (Although, they are trying to get our children filling out questionnaires, so there m,ay be a second generation.
The people who originated the study and ran it already retired after 25 years, and found another pair of researchers to hand it off to.
They track smoking behaviors and attitudes, whether or not our parents smoked, whether our spouses smoke (thanks to a suggestion from me back in the 90s, it now includes same-sex partners in the question :D), how we would feel if we knew our children smoked, if, and if so, how we would punish our children, but it also contains lots of lifestyle questions. It asks if we’ve ever been diagnosed with diseases X,Y,Z on a long list (like on an in-take form, and asks us how we personally feel out our tendency to take risks on a scale of 1-10, how likely we are to do things to go along with a crowd 1-10, and what our income bracket is. It asks us about our eating habits, and whether we are overweight, underweight, or on target. It’s all self-reported, but the questionnaires are processed under numbers.
The study is being done by Indiana University, and has had some of the results published, even though it is a longitudinal study, so results in many cases are tentative-- some are not, like IIRC, children are more likely to smoke if their parents EVER smoked, even if the parents had quit several years before the children started. (No one has done a study I can find on adopted children of non-smokers whose birthmothers smoked while pregnant, and how likely those people are to smoke, and I think that cries out to be done.)
Probably by the time more of this study is published, a lot of the OP’s questions will be answered.
If the OP thinks that risks associated with smoking are coincidental, and really associated with low income, or poor eating habits, drug use, or high risk behavior in general, I doubt it. The original studies back in the 1960 were done when smoking was more prevalent. Right now, about 22% of the population smokes, but when the first studies were done, it was more like 80%, and many of those who didn’t were asthmatic, or something. Of course, many of the additional smokers, smoked less. The 60% who quit almost immediately when they learned it was bad were often people who only smoked at parties, or just had one or two in the evening (according to my parents, who were the “smoke at parties” type).
But still, they had some risk, and incidence of smoking-related cancers did fall when smoking fell.
Smoking all by itself is dangerous. You can eat the best food, be in a high income bracket, go to the gym and work out every day, avoid every other bad thing in the world, always wear you helmet when you bike, get the HPV vaccine, and abstain from alcohol, but your smoking still puts you at risk.
My step-mother died at 97. She’d smoked (not heavily) all her life, but she died of bronchial infection even though she hadn’t been allowed to smoke for several years. Neither her, nor her children who are in their 60’s and 70’s and also smoke, have had cancer. So not everyone who smokes develops cancer. It’s just that statistically, you are far, FAR more likely to develop certain cancers if you do smoke.
I’m sure biochemists can suggest mechanisms by which tobacco smoke will trigger cancer. But as others point out, the “proof” is generally statistical; numerous studies over many years, compensating for any imagined bias, have consistently show this.
Second-hand smoke is a whole different issue - the main study I recall reading about used Japanese wives - their husbands smoked like chimneys in tiny confined apartments, so the concentration of smoke was much higher and exposure much more prolonged - so the statistical evidence was far easier to show. Similarly, children raised in smoking households tended to have a higher incidence of lung problems according to some studies…
(I do wonder if smoking in earlier years was really 80% (Among men, I presume?) I thought I had read at the peak it was 55% to 65% or so. I certainly do NOT miss the days when smokers and smoke was everywhere in public and at work.)
You get 80% figures when you count everyone who smoked at all. That includes pipe smokers who came home from work and puffed a pipe for a while, and that was it for the day, people who smoked only at parties, so they might smoke 3 or 4 cigarettes a month, or even go a whole month without smoking, couples who bought a pack on Friday, smoked it together over the weekend, and didn’t smoke at all during the week, college students who smoked when they needed to stay up to study, but otherwise didn’t smoke. There were women who smoked when they thought they needed to lose a few pounds, lost them and quit, then went through the cycle again six months later. There were all kinds of variations on being an occasional smoke, but all those people “counted” as smokers. The two-pack a day types accounted for about 20% of smokers, and that just a little less than the number of people who smoke now.
I infer from that that everyone who wasn’t actually addicted quit when the Surgeon General’s report on the dangers came out-- my mother certainly did, and made my father quit too. Neither found it difficult (according to my mother). The 20% of hard-core addicts couldn’t just quit, and didn’t.
And still, every generation, that percentage of people find their way to cigarettes.
As far as the number of people who smoked every single day, but didn’t smoke a whole pack a day, I don’t know about them. I suppose there were people who had an after-dinner cigarette, and that was it, but they had it every day. I’d really have to ask my mother, or someone else who was around back them. IIRC, from my one aunt who was still smoking in the 70s (she finally did quit), cigarettes get stale, and she used that as an excuse to smoke a pack before the cigarettes went bad, so a pack never lasted more than about three days for her.
Interesting. I don’t know that I really encountered “social smokers” but being almost 60, that’s probably a little before my time. People it seemed to me either smoked or they didn’t, and in the Good Old Days, that seemed to be a little over 50%. There were those who were always trying to quit… I don’t think I ever met anyone who “only smoked at parties” or that sort of habit. I suppose there were?
My youngest picked it up in the military, because his shop supervisor gave additional breaks if you smoked. He liked the work, but his supervisor drove him crazy, so a few minutes standing outside let him unclench.
He didn’t quit after he was discharged so much as it petered out once the reason for it wasn’t there any more. His brother, on the other hand, started in high school and was well and truly addicted. He quit a little more than a year ago because he wanted to start a family. He and his wife both went through hell quitting and I give them big props for it.
I can very well believe that there are genetic differences between those that get addicted and those who don’t.
A couple of things I’ve wondered about regarding smoking and lung cancer:
Is the risk primarily from “smoking tobacco” or from “smoking cigarettes”:?
The distinction is because modern cigarettes contain so many other ingredients besides tobacco to create different tastes among the brands.
Also, since about 1939 commercial tobacco has been grown using artificial nitrate fertilizer, which contains Polonium 210.
Yes, modern cigarette smoke is radioactive.
I wonder if there is an increased lung cancer rate since the cigarette smoke became radioactive.
I know that the rate of lung cancer no longer correlates with the number of smokers. Cancer is increasing while smoking is decreasing.
American Indians have historically lower rates of cancer compared to white Americans, but the rate among them is increasing.
They have a long history of tobacco use. Was the lung cancer rate lower when they grew their own tobacco instead of purchasing commercial cigarettes?
Cigarettes are radioactive because everything is radioactive. And inhaling any sort of smoke, tobacco or otherwise, will cause lung problems in the long term.
Also, while Native Americans have a long history of using tobacco, that’s mostly ceremonial use, not nearly as frequent as modern smokers.
