Major colorectal cancer aetiological hypotheses do not explain mortality trends among Maori and non-Maori New Zealanders.

New Zealand colorectal cancer mortality rates are presented for the period 1947-1980. Mortality has been increasing and is now the highest in the world for both males and females in the age range 35-64; indeed New Zealand mortality rates for those aged 35-44 are approximately twice those of other countries with high mortality. By contrast, colorectal cancer mortality rates among Maoris, the indigenous New Zealanders of Polynesian descent, have been decreasing so that they are now less than half the non-Maori mortality rates. These findings cannot be explained by ethnic differences in consumption of the major proposed dietary risk factors: total fat, cholesterol, meat, fibre and beer. Possible differences in the prevalence of lactose malabsorption, in faecal mutagen activity, and in the prevalence of colorectal polyps warrant further investigation.