Do socio-economic gradients in smoking emerge differently across time by gender? Implications for the tobacco epidemic from a pregnancy cohort in California, USA

Abstract

Understanding current patterns of population smoking by socioeconomic position (SEP) can be substantially enhanced by research that follows birth cohorts over long periods of time, yet such data in the US are rare. Information from birth cohorts followed during critical time periods when the health consequences of smoking became widely known can inform the ways in which current smoking prevalence has been shaped by the historical processes that preceded it. The present study utilizes data from a substudy of the Child Health and Development Study pregnancy cohort (N = 1612). Women were queried about smoking status in 1959–1962, 1971–1972 and 1977–1980. Women were divided into three cohorts based on date of birth. Offspring represented another birth cohort assessed for smoking in 1977–1980. Results indicated that the overall prevalence of smoking exhibited cohort-specific patterns that persisted across time. Notably, the youngest maternal cohort (born 1937–1946) had high smoking prevalence throughout and showed no appreciable decrease (44.7%, 41.4%, 40.1% for 1959–1962, 1971–1972, and 1977–1980). Results also indicated that the relation of smoking to SEP exhibited cohort-specific patterns over time. Among the oldest birth cohort (born 1914–1930), no inverse relation of SEP to smoking was observed at any time; in contrast, an inverse relation emerged by 1959–1962 among the youngest cohort of mothers. Among the adolescent offspring, there was a strong SEP gradient (OR = 2.0, 95% CI = 1.4–3.0) that was stronger than in any maternal birth cohort at any assessment (β = 0.40, SE = 0.1, p < 0.01). We conclude that SEP gradients in smoking emerge across birth cohorts rather than time alone, with increasingly strong gradients across time especially among younger cohorts.

Introduction

Understanding the health consequences of cigarette smoking has been one of the fundamental undertakings of epidemiologic research in the 20th century (Doll & Hill, 1954; Pearl, 1938), and the magnitude of the adverse effects of cigarette smoking on health continues to unfold (Doll, Peto, et al., 2004; Klebanoff, Levine, et al., 2001). While rates of smoking have declined in many high-income countries over the past thirty years (Pierce, 1989; Pierce, Messer, et al., 2011),a strong gradient in smoking by socioeconomic position (SEP) has simultaneously emerged in the U.S. as well as in many other high-income countries; low SEP is associated with higher probability of smoking (Chilcoat, 2009). Moreover, cigarette smoking in low-income countries is an increasing public health concern (Abdullah & Husten, 2004).

Despite an extraordinary body of research on cigarette smoking, there remain some fundamental gaps in our understanding of how health consequences of smoking arise across gender and socio-economic subgroups. An especially salient gap pertains to changes in cigarette smoking across birth cohorts of women in the 20th century, and the emergence of SEP gradients among women in these birth cohorts. These gaps hamper progress in the field by leaving open the question of how historical processes, policies, and norms shape cigarette consumption. As discussed by Lopez et al. (1994), countries often exhibit a predictable evolution of population-level tobacco use, with women consistently exhibiting lower overall prevalence, a lag in peak prevalence, and a slower decline compared to men.(Lopez, Collishaw, et al., 1994). This is evident in the US (Harris, 1983; National Cancer Institute, 1997) and other countries (Davy, 2006; Kemm, 2001). Data from repeated cross-sectional analyses of women indicate that prevalence of smoking increased among women of low socio-economic position during the 1970s and 1980s, during which time the prevalence of smoking among women with higher education and men with any education were leveling off or decreasing, both in the US (Escobedo & Peddicord, 1996) as well as Finland (Laaksonen, Uutela, et al., 1999) and the UK (Evandrou & Falkingham, 2002). Yet to our knowledge, no longitudinal cohort studies have examined evidence for birth cohort effects in the relation between SEP and smoking explicitly among women, during the pivotal period from 1960 to 1980, when the harmful effects of smoking became widely known.

A better understanding of the historical trends among women is critical for elaborating the implications of smoking for public health, developing policies to reduce smoking, and anticipating future trends in countries where smoking is on the rise. Evidence that rates of smoking initiation are now increasing among young women (Goodwin, Keyes, et al., 2009; Johnston, O'Malley, et al., 2007) further underscores the need to examine gender-specific smoking patterns. The present study utilizes a prospectively assessed sample of women representing various birth cohorts who were observed across 1959–1980 in the US. We use these data to examine trends by age, period, and cohort in cigarette smoking and in gradients by familial resources, as measured by husband's education, as a salient measure of SEP for this time period. Furthermore, to evaluate change across generations, we examine overall smoking prevalence and SEP gradient for the offspring of these women, interviewed in adolescence (age 15–18 years).