Geographical distribution of lung cancer mortality and environmental factors in Japan

Abstract

In order to study environmental factors related to the incidence of lung cancer (ICD 162), sex-specific standardized mortality ratios (SMRs) of lung cancer were calculated for 3297 basic autonomic units (91 wards, 629 cities, 1958 towns and 619 villages) in Japan, based upon the vital statistics for six years, 1964–1974. and sex- and age-specific population of each area in 1970. The SMRs were classified into five categories and depicted on a map for each sex.

These maps show that areas with high SMR of lung cancer tended to cluster in the highly urbanized and industrialized districts. However, some of these areas with high SMR were also widely scattered throughout Japan.

In an effort to study this geographical difference in areal mortality from lung cancer, analyses were carried out in two ways. First, the areas with high or low SMR were selected to examine the relationship between lung cancer mortality by sex and environmental characteristics; the high SMR group consists of the areas with SMR 120 or more and significantly higher than the average of Japan (112 areas for male and 74 for female), while the low SMR group of those with SMR less than 80 and significantly lower than the average (155 areas for male and 50 for female). Second, all of the areas were divided into two groups according to the existence of some environmental characteristics and the magnitude of SMRs were compared between these groups.

The results from the first analysis are as follows:

• 1.

  1. High SMR group in both sexes has significantly more air-polluted areas than low SMR group.

• 2.

  2. High SMR group of male but not female has significantly higher percentages of areas with metal refineries, steam power plants, oil refineries and coal mines than low SMR group.

• 3.

  3. Percentage of areas with metal mines in high SMR group is higher than that in low SMR group for both sexes, although the differences are not statistically significant.

The results from the second analysis are as follows:

• 1.

  1. Among the four categories of urbanization represented by ward, city, town and village, the more urbanized categories such as ward and city have the higher SMR of lung cancer.

• 2.

  2. The SMR is higher in the areas along the sea coast than in those without the coast regardless of the urbanization. The SMR is higher especially in male in the areas with fishing ports than in the other coastal areas without the ports.

• 3.

  3. The SMRs for both sexes are higher in the areas with steam power plants, coal mines or lignite mines than in the areas without these industries regardless of the urbanization.