Mortality of rheumatoid arthritis in Japan: A longitudinal cohort study

Masayuki Hakoda ^1*, Hiroshi Oiwa ², Fumiyoshi Kasagi ³, Naomi Masunari ², Michiko Yamada ², Gen Suzuki ² and Saeko Fujiwara ²

¹ Radiation Effects Research Foundation, Japan
² Department of Clinical Studies, Radiation Effects Research Foundation, Japan
³ Department of Epidemiology, Radiation Effects Research Foundation, Japan

^* To whom correspondence should be addressed. E-mail: hakoda{at}rerf.or.jp.

Accepted 14 March 2005

Abstract

Objective: To elucidate the mortality risk of Japanese patients with rheumatoid arthritis (RA), taking into account lifestyle and physical factors including comorbidity.

Methods: Ninety-one RA patients were identified in a screening of 16,119 Japanese individuals from a cohort of atomic bomb survivors during 1958 through 1966. Both RA patients and non-RA individuals of the cohort were followed for mortality until 1999. Mortality risk of RA patients was estimated by Cox proportional hazard model. In addition to age and sex, lifestyle and physical factors such as smoking status, alcohol consumption, blood pressure, and comorbidity were included as adjustment factors for the analysis of total mortality and also for the analysis of mortality due to each of different causes of death.

Results: Eighty-three (91.2%) RA patients and 8,527 (52.9%) non-RA individuals died during the average follow-up periods of 17.8 years and 28.0 years, respectively. Age and sex-adjusted hazard ratio for mortality in RA patients was 1.60 (95% confidence interval [95% CI] 1.29-1.99, P<0.001). Multiple adjustments including lifestyle and physical factors resulted in a similar mortality hazard ratio of 1.57 (95% CI 1.25-1.94, P<0.001). Although mortality risk tended to be higher in male RA patients compared with female patients, the difference was not statistically significant. Pneumonia, tuberculosis, and liver disease were significantly increased as causes of death in RA patients.

Conclusion: RA is an independent risk factor for mortality. Infectious events were associated with increased mortality in RA.

Keywords: Japanese, cohort study, mortality, rheumatoid arthritis, risk

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