Kerry Keyes and colleagues recently published a new article looking at changes in the relationship between smoking and psychiatric disorders across successive birth cohorts in the twentieth century. They find that as rates of smoking decreased through the latter half of the twentieth century, associations between smoking and psychopathology increased.
More from Keyes on this work and its implications below.
The fact that individuals who smoke are different than individuals who don’t smoke has beguiled observational epidemiology since the inception of studies aimed at assessing causal effects of smoking on health. Differences (on average) between smokers and nonsmokers include not only other substance use (e.g. alcohol consumption, caffeine intake), but also personality, temperament, and a myriad of other factors. Even in the early generation of tobacco research, Yurlshalmy (1971) noted that women who did not smoke when pregnant “in general appeared to live at a much slower and moderate pace than the smokers”.
I imagine Sandy Dee versus Rizzo for that particular analogy – though remember what happens when Sandy curls her hair and dons that exceptional black jump suit at the end of Grease – immediately a cigarette appears in her painted red lips. Not slow and moderate anymore Sandy!
The effects of smoking on health are so profound, consistent, and strong that the confounding of outcomes by factors that differ between smokers and nonsmokers did not (well, after several decades of strong evidence) deter the translation of epidemiological science into prevention implementation. Across the last 30 years, we have seen remarkable decreases in the proportion of the population in the United States who smoke. But this public health success begs a new question, with substantial implications for research – are people who continue to smoke today different than people who smoked 50 years ago?
Our research is demonstrating that yes, smokers today are different than those in previous cohorts. In fact, in two papers published in recent years [Here & Here], we showed that the association between nicotine dependence (not just causal puffing but consistent smoking throughout the day, feelings of craving when away from cigarettes for an extended period, and continued smoking despite attempts to quit, among other symptoms) and psychiatric disorders is stronger among smokers in younger generations. For example, compared with nicotine dependent individuals born in the 1940s and 1950s, those born in the 1960s, 1970s, and even 1980s were more likely to have concurrent drug and alcohol use disorders, attention deficit hyperactivity disorder, anxiety disorders, bipolar disorder, and antisocial personality disorder. These associations became stronger with each decade of younger birth.
Overall, this suggests that smokers today have a much heavier burden of psychopathology than in the past. There are several implications of this for research and public health practice. First, untreated psychopathology makes quitting smoker harder. Thus, cessation efforts may be stalled unless psychopathology, which is increasingly associated with smoking, is addressed. Practitioners as well as those engaged in new public health efforts must be aware that efforts to reduce smoking need to take into account the increasing associations between smoking and a host of potential other problems. Second, these results have implications for how we study nicotine dependence. For example, genetic epidemiologists continue to hunt for genes that explain why some individuals become addicted to cigarettes after starting whereas others can drop the habit. But when a particular sample of smokers was enrolled into a study matters for our ability to detect such genes. That is, samples of smokers collected more recently are going to have a higher burden of other psychopathology, which likely also has, at least in part, a genetic basis, adding to potential confounding and creating non-comparability across study samples collected in different decades.
Two other final points. While smoking has declined in the US, it remains among the most prevalent preventable causes of disease both in the US and worldwide, and remains very prevalent in many other nations, portending a huge public health burden in decades to come. Stigmatizing individuals who smoke as flawed, or having a moral failing, or as lacking will power to quit is unhelpful, and efforts to improve access to cessation tools as well as concurrent management of other health problems faced by smokers, including mental health problems, may be an important road towards reducing smoking levels both in the US and elsewhere.