Fish consumption and risk of breast, colorectal and prostate cancer: a critical evaluation of epidemiological studies

Consumption of fish and risk of colon cancer in the Norwegian Women and Cancer (NOWAC) study

Recent studies have shown a decreased risk of colon cancer with consumption of fish. However, most studies on fish consumption do not distinguish between lean and fatty fish, or between poached and fried fish. The aim of this study was to investigate any association between fish consumption and colon cancer in The Norwegian Women and Cancer (NOWAC) study. We focused mainly on lean fish, which was further divided into poached and fried fish. A total of 63 914 women were included in the analysis, 254 of whom were found to have colon cancer during follow-up. Since fish consumption was one of the main topics of interest in the NOWAC study, there is a predominance of women from northern Norway due to higher fish intake in this area; hence the study is not representative of the whole of Norway. The participants completed a semi-quantitative FFQ between 1996 and 1999, and were followed-up for incidence of colon cancer until 2004. No association between fish consumption and risk of colon cancer was seen, except for the third tertile of poached lean fish consumption (relative risk (RR) 1.46, 95 % CI 1.04, 2.06). This association disappeared when excluding women with less than 1 year of follow-up. In conclusion, the present study does not support the hypothesis of a protective effect of fish against colon cancer risk.

Cancer in the Sami population of North Norway, 1970-1997

The Sami population in North Norway constitutes an ethnic minority with a lifestyle that diverges from that of the rest of the population. A cohort of 19 801 people of Sami origin was followed for cancer incidence over the period 1970-1997 by the Norwegian Cancer Registry. Among the Sami 1340 cases of cancer were observed versus 1658.2 expected, based on a regional reference population. For both sexes a significantly decreased incidence of colon cancer was observed. The standardized incidence ratio (SIR) for men was 0.50 (95% confidence interval (CI) 0.34-0.71) and for women 0.62 (95% CI 0.43-0.85). Low SIRs were observed for lung cancer: 0.63 (95% CI 0.51-0.77) and 0.60 (95% CI 0.37-0.91), for men and women, respectively. Men of Sami ancestry had a decreased risk of prostate cancer: SIR 0.57 (95% CI 0.45-0.71). Among women 127 cases of breast cancer were observed versus 149.6 expected. A relatively high physical activity and a diet rich in fish may in part explain the low cancer incidence. Some Sami were exposed to radioactivity as a result of their diet based on reindeer products. Adverse effects on their cancer incidence were not observed.