Low Level Carbon Monoxide and Mortality of Persons Aged 65 or Older in Tokyo, Japan, 1976-1990

Abstract

Ambient carbon monoxide (CO) levels in most of the cities in Japan have not exceeded the National Air Quality Standard. We investigated whether or not this low level of CO pollution has been positively related to the mortality rate. We used computerized data for Tokyo, 1976-1990, obtained from governmental agencies. Subjects were restricted to those 65+ years old, because air-pollution influences this group the most. Although the CO level was higher in earlier years and was correlated with the sulfur dioxide level, the Poisson regression analysis that included chronological year and sulfur dioxide level as covariates showed a positive association between CO level and all-cause mortality rate: The mortality rate ratios for the CO levels 1.1-1.6, 1.6-2.2, 2.2+ ppm compared with the CO level < 1.1 ppm were 1.017 [95% confidence interval (CI) 1.009-1.026], 1.031 (95% CI 1.020-1.041) and 1.051 (95% CI 1.039-1.063), respectively. Although it is possible that the higher CO levels only displace deaths several days earlier, the results warrant further study as to whether or not further reduction of CO level would improve the mortality rate of the elderly.