I think parent comment was pointing to lack of establishing a causation link. The finding in their abstract is extrapolated by statistical inference. For example smokers tend to drink more etc. The paper does take such factors into account. Personally I wouldn't jump to such a strong conclusion from statistical inference because it closes the door on other factors that might be even stronger when combined together. The paper reflects motivated reasoning more than a discovery outcome. That said, smoking is of course a major health risk, I am just pointing at the research approach.
In the paper they claim it matters for midlife mortality too:
> People who start smoking at age 18 begin to exhibit higher mortality several decades later, with particularly large effects beginning at ages 45–64 (Lawton et al. 2025). A health-capital model allows the mortality rates of older persons to be determined not only by their current smoking behavior but also by smoking in earlier years. In the United States, smoking rates started falling for college graduates earlier than they did for the non-college population.
...
> [...] with rapidly improving treatments and screening for lung cancer (Howladeret al. 2020), the major impact of smoking over the longer-term—particularly for people aged 55–64 arises from other more-common tobacco-related diseases such as chronic obstructive pulmonary disease (COPD); cardiovascular diseases such as strokes, aneurysms, and heart
attacks; diabetes; and other types of cancers (Carter et al. 2015). Perhaps more surprising is that past county-level smoking rates are highly predictive of deaths of despair. This finding, however, is consistent with an emerging literature in biology that points to a causal influence
of smoking on drug addiction [...]