Last week, the mainstream press reported a study that linked consumption of fish oil to prostate cancer. A closer look at the study, however, calls the headline into question. The results were taken from a study that was designed to answer the association between selenium and vitamin C and cancer risk. The study was not initially designed to study the link between omega 3 oils and prostate cancer risk. The researchers included one (just one) measurement of blood levels of omega 3 oils. It is always dangerous to use a study designed for a specific purpose, such as selenium and vitamin C intake and cancer risk in general to answer a specific question about another factor such as fish oil consumption. One measurement in time gives no information about any subject's daily intake in a disease that takes years to develop. The difference between the two groups, those with increased risk and the control was 4.66% vs. 4.48%. This is at best a weak correlation and not causation.