Omega 6 y cancer

REVIEW

Effects of Omega-3 Fatty Acids on Cancer Risk
A Systematic Review
Catherine H. MacLean, MD, PhD Sydne J. Newberry, PhD Walter A. Mojica, MD, MPH Puja Khanna, MD Amalia M. Issa, MPH, PhD Marika J. Suttorp, MS Yee-Wee Lim, MD, PhD Shana B. Traina, MA Lara Hilton, BA Rena Garland, BA Sally C. Morton, PhD
TUDIES SHOW THAT TISSUE LEVels of arachadonic acid– and eicosopentaenoic acid(EPA)– derived eicosanoids influence many physiological processes, including calcium transport across cell membranes, angiogenesis, apoptosis, cell proliferation, and immune cell function.1-4 These processes are integral to the immune system and hence the pathogenesis of autoimmune diseases such as arthritis, systemic lupus erythematosus, and asthma, as well as cancer. Epidemiological studies havesuggested that groups of people who consume diets high in omega-3 fatty acids may experience a lower prevalence of some types of cancer,5-8 and many small trials have attempted to assess the effects of omega-3 fatty acids on cancer treatment by adding omega-3 fatty acid to the diet either as omega-3 fatty acid–rich foods or as dietary supplements.9-22 In addition, dietary omega-3 fatty acids have beenfound to modulate mammary tumor formation and proliferation in rodents.23 In response to this evidence, a number of omega-3 fatty acid–containing dietary supplements have appeared on the

Context Omega-3 fatty acids are purported to reduce the risk of cancer. Studies have reported mixed results. Objective To synthesize published and unpublished evidence to determine estimates of the effect ofomega-3 fatty acids on cancer risk in prospective cohort studies. Data Sources Articles published from 1966 to October 2005 identified through MEDLINE, PREMEDLINE, EMBASE, Cochrane Central Register of Controlled Trials, and CAB Health; unpublished literature sought through letters to experts in the neutraceutical industry. Study Selection A total of 38 articles with a description of effects ofconsumption of omega-3 fatty acids on tumor incidence, prospective cohort study design, human study population; and description of effect of omega-3 among groups with different levels of exposure in the cohort were included. Two reviewers independently reviewed articles using structured abstraction forms; disagreements were resolved by consensus. Data Extraction Two reviewers independently abstracteddetailed data about the incidence of cancer, the type of cancer, the number and characteristics of the patients, details on the exposure to omega-3 fatty acids, and the elapsed time between the intervention and outcome measurements. Data about the methodological quality of the study were also abstracted. Data Synthesis Across 20 cohorts from 7 countries for 11 different types of cancer and using upto 6 different ways to categorize omega-3 fatty acid consumption, 65 estimates of the association between omega-3 fatty acid consumption were reported. Among these, only 8 were statistically significant. The high degree of heterogeneity across these studies precluded pooling of data. For breast cancer 1 significant estimate was for increased risk (incidence risk ratio [IRR], 1.47; 95% confidenceinterval [CI], 1.10-1.98) and 3 were for decreased risk (RR, 0.68-0.72); 7 other estimates did not show a significant association. For colorectal cancer, there was 1 estimate of decreased risk (RR, 0.49; 95% CI, 0.27-0.89) and 17 estimates without association. For lung cancer one of the significant associations was for increased cancer risk (IRR, 3.0; 95% CI, 1.2-7.3), the other was for decreasedrisk (RR, 0.32; 95% CI, 0.13-0.76), and 4 other estimates were not significant. For prostate cancer, there was 1 estimate of decreased risk (RR, 0.43; 95% CI, 0.22-0.83) and 1 of increased risk (RR, 1.98; 95% CI, 1.34-2.93) for advanced prostate cancer; 15 other estimates did not show a significant association. The study that assessed skin cancer found an increased risk (RR, 1.13; 95% CI,...