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Keywords:

  • animal fat;
  • colon neoplasms;
  • descriptive epidemiology;
  • meat;
  • rectal neoplasms;
  • time trends

Abstract

  1. Top of page
  2. Abstract
  3. REFERENCES

We examined trends of colorectal cancer incidence rates among Japanese (Miyagi Prefecture) and United States (US) whites (State of Connecticut) between 1959 and 1992. Age-standardized rates in Japan have increased dramatically and are now similar to US white rates. For both colon and rectum, age-specific rates in Japanese men born after 1930 exceed those in US whites, and the Japanese excess increases with year of birth. Similar patterns are evident for women. The current trends suggest that colorectal cancer will become a major source of morbidity and mortality in Japan, as these young Japanese age and their risks increase. © 2004 Wiley-Liss, Inc.

In the mid-twentieth century, colorectal cancer incidence was substantially lower in Japan than in the United States (US). However, Japanese rates have been increasing rapidly.1, 2, 3 The increases may reflect lifestyle changes occurring in Japan since World War II, such as increased consumption of animal fat and meat, and decreased energy expenditure. These characteristics have been associated with increased colorectal cancer risk.4, 5

Here we plot colon and rectal cancer incidence rates in Japanese (Miyagi Prefecture) and US whites (state of Connecticut) for men and women during the period 1959–1992, obtained from volumes I–VII of Cancer Incidence in Five Continents (CI5).6, 7, 8, 9, 10, 11, 12 We chose the Miyagi Prefecture Cancer Registry for the Japanese and the Connecticut Tumor Registry for US whites because they covered the longest time period, with incidence data reported in all of the 7 volumes of CI5.

Figure 1a shows age-standardized incidence rates per 100,000 person-years in the 2 populations by 5-year calendar periods defined by the CI5 series. We computed age-standardized rates, truncated to 40–74 years of age, using the world standard population. Rates among Japanese have increased over the entire period for both sexes. In contrast, rates among US white men increased gradually from 1960 until the mid-1980s and then declined thereafter. Rates among US white women remained constant until the mid-1980s and then declined. Rectal cancer rates present similar patterns (Fig. 1b).

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Figure 1. (a,b). Age-standardized incidence rates (cases per 100,000 person-years) of colon (a) and rectal (b) cancer (standardized to the world standard population, truncated to 40–74 years of age) for Japanese (Miyagi Prefecture) and US whites (State of Connecticut). C. Per capita daily consumption of meat and animal fat in Japan and the US (Source: Food and Agricultural Organization13).

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Figure 1c shows trends in per capita consumption of meat and animal fat in Japan and the US during the period 1961–1991 that was obtained from the Food and Agricultural Organization (FAO) database.13 Consumption of meat has been substantially higher in the US than in Japan throughout the period examined, and it has increased in both countries, with higher rates of increase observed in Japan. Animal fat consumption has decreased dramatically in the US and increased moderately in Japan. A comparison of Figures 1a,b with Figure 1c indicates that the age-adjusted incidence trends for both colon and rectal cancers are similar to the trends in animal fat consumption.

National data on trends in cancer incidence and food disappearance data are inappropriate for causal inferences. Nevertheless, a comparison of trends may motivate hypotheses that could be tested in analytic studies.14 The low rates of meat consumption in Japan compared with the US suggest that changes in meat consumption do not explain the observed incidence trends in Figure 1. The trends in animal fat consumption appear to parallel the incidence trends more closely, and yet animal fat consumption in recent years in Japan is only about half that in the US. A more formal analysis would model incidence as a lagged function of food consumption to allow for a cancer induction period, but such detailed analysis seems inappropriate given the limitations of these ecological data. The Japanese may be more susceptible to the effects of dietary risk factors than are US whites. Such variation in susceptibility could reflect genetic modulation of colon cancer risk due to dietary risk factors. For instance, the Japanese and US whites may have different allele frequencies of polymorphisms that control detoxification of food-derived carcinogens.15 The increasing colon cancer risk in native Japanese may also be explained by changes in exposure to other risk factors, such as sedentary lifestyle, body size and alcohol intake.4, 5

Figures 2 and 3 show age-specific incidence rates of colon and rectal cancers, respectively, by birth cohort. For both cancers, age-specific rates in Japanese men born after 1930 have exceeded those of US whites, and the Japanese excess increases with year of birth. Similar patterns are evident for women.

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Figure 2. Age-specific incidence rates of colon cancer for Japanese (Miyagi Prefecture) and US whites (State of Connecticut) by birth cohort (1926–1930 to 1941–1945).

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Figure 3. Age-specific incidence rates of rectal cancer for Japanese (Miyagi Prefecture) and US whites (State of Connecticut) by birth cohort (1926–1930 to 1941–1945).

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The data in Figures 2 and 3 show that colorectal cancer rates in younger generations of Japanese now equal or exceed those in their US white counterparts. Lifestyle changes related to economic development and Westernization in Japan probably were greatest in the 1960s and 1970s.16,17 The full impact of increased exposure to risk factors may not become evident for several decades, when Japanese exposed to these factors since young age reach their sixth and seventh decades of life. The current trends suggest that colorectal cancer will become a major source of morbidity and mortality in Japan, as these young people age and their risks increase.

REFERENCES

  1. Top of page
  2. Abstract
  3. REFERENCES
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