Smoking trajectories, health, and mortality across the adult lifespan

Abstract

This study extends research on the association between smoking behavior and chronic disease by following a cohort from the time of initiation of regular smoking patterns into old age and by examining the association of lifetime smoking trajectories with chronic disease and mortality. Participants consisted of 232 males selected from the Harvard classes of 1942–1944 and followed biennially through 2003. Five distinct smoking trajectories were identified based on the age at which participants quit daily smoking. Participants following smoking trajectories with later cessation had a higher likelihood of developing lung disease and lived shorter lives than those who quit smoking at an earlier age. This study confirms that the earlier a smoker quits, the greater the health benefits, and that these benefits are observed even decades after smoking cessation. Additionally, by showing different survival rates between trajectory groups 25 and 40 years after quitting, the results run counter to previous work that has found no difference in mortality between smokers and non-smokers 15 years after cessation.

Introduction

Smoking, the single most preventable cause of premature death in the United States, results in 440 000 deaths annually (MMWR, 2003). Retrospective reports have indicated that smoking is associated with specific negative health outcomes, including several types of cancer, as well as cardiovascular and respiratory diseases (USDHHS, 2004). Prospective work has confirmed many of these associations (Engeland et al., 1996, Freund et al., 1993, Giovannucci et al., 1994, Godtfredsen et al., 2005, Hirdes et al., 1987, Howard et al., 1998, Lam et al., 1997, Nusselder et al., 2000, Ostbye and Taylor, 2004, Ostbye et al., 2002, Prescott et al., 1998, Prescott et al., 1998, Simons et al., 2005, Wannamethee et al., 2001, Weir and Dunn, 1970, Yuan et al., 1996) and has demonstrated a temporal ordering suggesting the likelihood of a causal relationship between smoking and these disease outcomes.

Most often, prospective studies are conducted over short periods, with few following study participants for longer than a decade (Giovannucci et al., 1994, Howard et al., 1998, Ostbye et al., 2002, Weir and Dunn, 1970, Yuan et al., 1996), and many measuring smoking behavior during only one assessment (Engeland et al., 1996, Enstrom, 1999, Hirdes et al., 1987, Lam et al., 1997, Rogot and Murray, 1989). Among studies of United States populations with the longest periods of repeated longitudinal smoking assessment, including the Framingham Study (Freund et al., 1993, Freund, 1992, Gordon et al., 1975) and the First Cancer Prevention Study (CPS-I) (Knoke et al., 2004, Thun et al., 1995, Thun and Heath, 1997), baseline smoking behavior is captured at entry through reports by adults who have long passed the age of risk for smoking initiation and established use. Because most smokers quit and relapse repeatedly before abstaining permanently, short term, compressed, and averaged smoking measurements are necessarily simplifications of the quitting process (USDHHS, 1990), and fail to maximally characterize changes in smoking behavior across the lifespan.

One analytic approach that better captures smoking behavior is latent class growth analysis (LCGA), which seeks to identify population subgroups that follow distinct behavioral trajectories (Muthén and Muthén, 2000, Nagin, 1999). While prospective work using such analysis has defined trajectories of smoking behavior within adolescence and across early adulthood (Chassin, Presson, Pitts, & Sherman, 2000), trajectories across the lifespan have not been empirically characterized, nor has the association between smoking trajectories and disease been investigated. The present study aims to extend previous research in the following ways: (1) by following a cohort from the time of initiation of regular smoking patterns (i.e., age 21) into old age (i.e., age 82), when chronic illness is most likely to impact health and longevity; and (2) by evaluating the association between an individual's tendency to follow a particular smoking trajectory and chronic diseases and mortality.