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Trends in diet-related cancers in Japan:a conundrum?

SIR-Changes in cancer risk with different levels of dietaryintake, if they exist, are small.’ Much of the dietary hypothesiswas based on correlations with increases in "diet-related"

cancers, in particular the "westernisation" of the Japanese dietand especially a high intake of fat and meat and cancer of thebreast, colorectum, and prostate. We have examined trends inmortality from these cancers in Japan with the WHO mortalitydatabase over the past three decades.

Mortality from intestinal cancer, mainly colorectal cancer,has steadily increased in Japan over the past three decades2 withthe all-ages, age-standardised mortality rate in males risingfrom 7-0 per 100 000 in 1955-59 to 14-6 per 100 000 in 1985-89.The truncated rates, restricted to ages 35 to 64, have alsoincreased from 97 to 19-4. Among females, colorectal cancermortality rose from 6-0 to 9-5 over all ages and from 9-2 to 13-3over the truncated range. Even these more recent rates ofcolorectal cancer are considerably lower than those registeredin North America and in several northern and central Europeancountries, but are compatible with rates in Finland, Sweden,and most Mediterranean countries.3,4These increases are impressive and have been taken to

correspond to the effects of the introduction of a westerniseddiet, with younger people moving towards the high-fat,high-meat diet typical of north America and western Europe.However, over the past decade the trends in younger

generations of Japanese of both sexes born after 1945 havereversed (figure). In 1985-89, Japanese men and women aged30-34 and 35-39 (ie, born around 1950) had colorectal cancermortality rates similar to those born in the late 1920s and 1930s.

Breast cancer mortality in Japanese women of all ages rosefrom 39 per 100 000 in 1955-59 to 6.1 in 1985-89. The

1875 1885 1895 1905 1915 1925 1935 1945 1955

- Central year of birth

Figure: Trends in age-specific death certification rates fromIntestinal cancer in men and women in Japan, 1955-89

corresponding truncated-age rates were 8-4 and 144,respectively. In terms of birth cohort, rates among cohortsborn this century have steadily increased with no evidence ofany alteration in the trends.

Prostate cancer mortality rose from 1.2 per 100000 in

1955-59 to 3-6 in 1985-89. In contrast to this large increase, thetruncated rates rose from 0-8 8 to 1 3 over the same period. Therehave been previously increasing trends in successive birthcohorts which may now be stabilising or falling amongincreasingly younger cohorts.The reversal of trends in colorectal cancer and prostate

cancer is difficult to reconcile with what was expected in view ofchanging diet. The evidence of an association with westerndiet, especially high intake of fat and meat, is strongest forcolorectal cancer. Cohorts of Japanese born after the SecondWorld War have been more widely exposed to thewesternisation of their diet, but their risk of colorectal cancerand prostate cancer appears to be declining. Improvements indiagnosis and therapy are unlikely to have had such a majorimpact on mortality from colorectal and prostate cancer. Bycontrast, the increase in breast cancer mortality within birthcohorts continues although the increases seem to have affectedwomen born since the start of this century and there does not

appear to have been an acceleration among the youngestcohorts of women.

In the absence of major differences in aetiological andbiological correlates of these forms of cancer in younger andolder ages, recent trends in the younger cohorts would suggestthat the decline in colorectal cancer can be expected to continueto middle age and beyond, and that the colorectal and prostatecancer mortality rates in Japan may never reach rates similar tothose of several western countries. These suggestions, and thecontradictions apparent in the cohort-based trends in Japan, Ipose continuing challenges for epidemiological research.

Peter BoyleDivision of Epidemiology and Biostatistics, European Institute of Oncology, 20141Milan, Italy

Rabio Kevi, Franca LucchuniRegistre Vaudois des Tumeurs, Institut Universitaire de Medecine Sociale etPreventive, Centre Hospitalier Universitaire, Vaudois, Lausanne, Switzerland

Carlo La Vecchia

Istituto di Richerche, Farmacologische ’Mario Negri’, and Institute of Biometry,University of Milan

1 Boyle P, La Vecchia C. The causes of cancer. In: Peckham MJ, PinedoH, Veronesi U, eds. Oxford textbook of oncology. Oxford: OxfordUniversity Press (in press).

2 Wynder EI, Fujita Y, Harris RE, Hirayama T. Comparativeepidemiology of cancer between the United States and Japan: a secondlook. Cancer 1991; 67: 746-63.

3 La Vecchia C, Lucchini F, Negri E, Boyle P, Maisonneuve P, Levi F.Trends of cancer mortality in Europe, 1955-1989: I, digestive sites.Eur J Cancer 1992; 28: 132-235.

4 La Vecchia C, Lucchini F, Negri E, Boyle P, Levi F. Trends in cancermortality in the Americas, 1955-89. Eur J Cancer 1993; 29A: 431-70.

5 Willett WC. The search for the causes of breast and colon cancer.Nature 1989; 338: 389-94.

Corrections

Essential fatty acid supplementation in atopic dermatitis—In this letter byDr J Berth-Jones and colleagues (Aug 7, p 377), the sentence that begins online 10 of the third paragraph should have read, "Only 55 (45%) of 123subjects enrolled were using potent or very potent compounds, and most ofthese were among the mildest in the potent group".

New life for old medicine.—In this Tokyo Perspective by Catrien Ross (Aug21, p 485) the prescription market for kampoyaku stands at Y161 billion (notmillion).