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BMJ 2006; 332 doi: (Published 02 February 2006) Cite this as: BMJ 2006;332:289
  1. Alison Tonks, associate editor (

    Omega 3 fatty acids do not prevent cancer

    Omega 3 fatty acids are unlikely to prevent cancer, write researchers from the United States. In 38 cohort studies they found 65 estimates of the association between omega 3 intake and 11 types of cancer. Only 10 of the estimates were statistically significant, and six of those suggested an increased not a decreased risk of cancer.

    Credit: JAMA

    The studies were all prospective and reported the effects of omega 3 intake—often from fish—in 20 cohorts of more than 700 000 people who were followed up for up to 30 years. More than half the studies were of breast, prostate, or colorectal cancer.

    If a literature spanning at least 20 years is essentially negative, where did the original notion come from? Probably the laboratory: omega 3 fatty acids influence angiogenesis, cell proliferation, apoptosis, and the immune system, so a link with cancer is biologically plausible. Experiments on laboratory animals also suggest that these fatty acids can suppress some kinds of tumours, although not much. Finally, epidemiological work has hinted that populations with a diet rich in omega 3 fatty acids have a lower prevalence of cancer.

    This early circumstantial evidence was probably wrong, write the authors. Laboratory animals eating a diet spiked with toxic doses of fatty acids are very different from ordinary people eating more or less fish. Despite a thorough and detailed search, they could find no good evidence that omega 3 fatty acids protect humans from cancer.

    Use your sense of smell

    You can tell a lot about a patient from the way he or she smells, writes one US doctor. It's often the most obvious thing about them, particularly when they are confined in a closed room. In his first year as a resident he quickly learnt to identify infected diabetic feet or the whiff of a mucky tracheostomy. The telltale smell …

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