Session Title: Epidemiology/Public Health
Session Type: Abstract Submissions (ARHP)
Background/Purpose: To examine birth cohort and period effects in the age-trajectories of reported arthritis from 1994 to 2010 in a representative sample of Canadians; and to determine whether any birth cohort or/and period effects in reported arthritis are associated with differences in SES (education and income), smoking, physical activity, or obesity over time.
Methods: Data from the Canadian Longitudinal National Population Health Survey, a nationally representative community sample followed every 2 years for 18 years. We used data for four birth cohorts (n =8,809 at baseline): World War II generation, born 1935-1944; older baby boomers, born 1945-1954; younger baby boomers, born 1955-64; and generation X, born 1965-74. Data at each interview included self-reported arthritis diagnosed by a health professional, years of education, household income, smoking, index of physical activity, and height (m) and weight (kg) (used to calculate body mass index (BMI: wt/ht2)). Multilevel growth models were used to estimate the age-trajectory for reported arthritis for each cohort accounting for period. Once the age-trajectory was established, education, household income, smoking, physical activity, and BMI were separately introduced into the models to examine their influence on arthritis.
Results: There was a trajectory of increasing prevalence of arthritis with increasing age in all cohorts, with younger cohorts having successively greater prevalence. After accounting for period effects the cohort effect was no longer apparent. There were marked population-level cohort effects for increasing education, income, physical activity, and BMI and decreasing smoking from the youngest to oldest cohorts, which were much reduced (education, smoking, and physical activity) or removed (income and BMI) once period was taken into account. Including these variables in a multi-level growth model showed the prevalence of arthritis was significantly lower (p<.001) in those with higher education (OR: 0.54; 95% CI: 0.44 – 0.65: >16 years vs <12 years of school) or higher income (OR: 0.60; 95% CI: 0.53 – 0.68: highest vs lowest quartile) and the prevalence was significantly higher for obese individuals (OR: 2.63; 95% CI: 2.20 – 3.14: BMI>=35 vs normal BMI (18.5-24.9) and current smokers vs non-smokers (OR: 1.63; 95% CI: 1.42 – 1.88). Physical activity was not significantly associated with arthritis. Further analysis showed that the population-level effects of increasing education and income on reducing the arthritis prevalence were almost counter-balanced by effects of increasing BMI (obesity).
Conclusion: The findings suggest that the cohort effect of more arthritis in younger cohorts is explained by period effects such that the potential benefits of increased education and income in reducing the prevalence of arthritis have been partially offset by increases in BMI over time. Our understanding of the impact of BMI on arthritis is therefore likely to be an underestimate. The cohort effect of increased arthritis in younger cohorts also suggests that previous population projections may be underestimated.
E. M. Badley,
A. V. Perruccio,
M. A. M. Gignac,
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ACR Meeting Abstracts - https://acrabstracts.org/abstract/a-longitudinal-population-based-study-1994-2010-of-age-period-and-cohort-effects-in-the-prevalence-of-arthritis-the-effect-of-improving-socioeconomic-status-and-increasing-obesity-over-time/