Working night shifts can be hazardous to health. Women who work rotating night shifts face an increased risk of developing colorectal cancer, a new prospective observational study has found (Journal of the National Cancer Institute 2003;5:825-8).

Researchers led by Dr Eva Schernhammer of Harvard Medical School in Boston, Massachusetts, and from the Ludwig Boltzmann Institute of Applied Cancer Research in Vienna, Austria, uncovered this link by following 78 586 women nurses who were enrolled in a longitudinal epidemiological study known as the nurses health study.

The investigators used a prospective observational design—that is, the participants in the study were enrolled before developing tumours of the large bowel and were observed throughout the course of the study, which lasted from 1988 to 1998.

The researchers tried to control for possible confounding factors such as age, physical activity, smoking history, socioeconomic status, sigmoidoscopy screening, nutritional intake, and use of multivitamins, calcium, aspirin, and oral contraception.

Women who had a history of any cancer …