BACKGROUND AND AIMS: Tobacco smoking has declined dramatically in many high-income countries over the past seventy years. Studies that have mapped this trend have relied on repeat cross-sectional or retrospectively measured smoking data, which have limitations regarding accurate measurement, inclusion of early smokers, and capturing of within-person change over time. Here, we introduce a new resource detailing harmonisable smoking data in four British birth cohort studies spanning 1946-2018 and use these data to document age and cohort changes in smoking.

DESIGN: Longitudinal data from four nationally representative British Birth Cohort Studies, born 1946, 1958, 1970 and 2000/02, respectively.

SETTING: Great Britain.

PARTICIPANTS: 50 942 participants were eligible for inclusion in this study (5362 in the 1946c, 16 178 in the 1958c, 16 036 in the 1970c, and 13 366 in the 2001c). Data collection spanned the years 1946-2018.

MEASUREMENTS: Prevalence of daily smoking and cigarettes smoked per day were measured prospectively at various points across the life course via self-report.

FINDINGS: The prevalence of smoking and the average number of cigarettes smoked by daily smokers declined between each successive cohort. At age 42/43y, prevalence of daily smoking was 33.6% (95% confidence interval [CI] = 31.8%, 35.5%) in the 1946c, 27.3% (95% CI = 26.5%, 28.2%) in the 1958c, and 22.1% (95% CI = 21.3%, 22.8%) in the 1970c. Males smoked more and with greater intensity than females, on average, though sex differences were smaller in latter cohorts. Within a cohort, the prevalence and intensity of smoking peaked in early adulthood (< age 30y) and declined thereafter; participants who continued to smoke daily smoked fewer cigarettes as they grew older.

CONCLUSIONS: In Great Britain, smoking prevalence and cigarette consumption appear to have declined substantially between cohorts born across the latter half of the twentieth and early twenty-first centuries. The British Birth Cohorts represent a unique and largely underutilized resource for investigating trends in smoking across life (prenatal to old age) and by year of birth (1946-2001), including changes in the determinants, correlates, and consequences of smoking. We provide syntax and information on items on smoking in these cohorts to catalyse future research, also available at: https://cls-data.github.io/smoking-in-the-cohorts/.