Vegetarianism and colorectal cancer risk in a low-selenium environment: effect modification by selenium status? A possible factor contributing to the null results in British vegetarians

BACKGROUND: Despite the consistent findings of lower total cancer incidence in vegetarians than in meat-eaters in the UK, the results of studies of colorectal cancer (CRC) risk in British vegetarians have largely been null. This was in contrast to the hypothesis of a decreased risk of CRC in this population due to null intake of red and processed meats and increased intake of fibre. Although the data are inconsistent, it has been suggested that selenium (Se) status may influence CRC risk. METHODS: A literature review was performed of studies on CRC risk in vegetarians, Se intakes and status in vegetarians, and changes of Se intakes and status in the UK throughout the follow-up periods of studies on CRC risk in British vegetarians. RESULTS: Vegetarians in the UK and other low-Se areas were found to have low Se intakes and status compared to non-vegetarians. There was some evidence of a reverse J-shaped curve of Se intakes and status in the UK throughout the last three decades. These presumed patterns were followed by the changes in CRC mortality or incidence in British vegetarians during this period. CONCLUSIONS: Available data on Se intake and status in British vegetarians, as well as the relationship between their secular changes in the UK and changes in CRC risk in this dietary group, are compatible with the hypothesis that low Se status may contribute to the largely null results of studies of CRC risk in vegetarians in the UK.