Effect of omega 3 fatty acid supplementation on cancer incidence non vascular death, and total mortality; a meta analysis of randomized controlled trials
Effect of omega 3 fatty acid supplementation on cancer incidence non vascular death, and total mortality; a meta analysis of randomized controlled trials
Year: 2014
Authors: Zhang, Y.F. Gao, H.F. Hou, A.J. Zhang, Y.H.Z.
Publication Name: BMC Public Health
Publication Details: Volume 14:204. doi: 10.1186/1471-2458-14-204.
Abstract:
Omega 3 fatty acids are known to prevent cardiac death. However, previous observational studies have suggested that omega 3 fatty acids are associated with cancer risk in adults. We conducted a meta analysis based on randomized controlled trials to evaluate the effect of omega 3 fatty acids on the risk of cancer incidence, nonvascular death, and total mortality. In February 2013, we performed electronic searches in PubMed, EmBase, and the Cochrane Library to identify randomized controlled trials on cancer incidence, nonvascular death, and total mortality. Relative risk (RR) was used to measure the effect of omega 3 fatty acid supplementation on the risk of cancer incidence, nonvascular death, and total mortality using a random effect model. The analysis was further stratified by factors that could affect the treatment effects. Of the 8,746 identified articles, we included 19 trials reporting data on 68,954 individuals. These studies reported 1,039 events of cancer, 2,439 events of nonvascular death, and 7,025 events of total mortality. Omega 3 fatty acid supplementation had no effect on cancer incidence, nonvascular death, or total mortality when compared to a placebo. Subgroup analysis indicated that omega 3 fatty acid supplementation was associated with a reduction in total mortality risk if the proportion of men in the study population was more than 80 per cent, or participants received alpha linolenic acid. Omega 3 fatty acid supplementation does not have an effect on cancer incidence, nonvascular death, or total mortality. (Authors abstract)
Omega 3 fatty acid supplementation has been suggested to reduce the risk of cancer incidence, including that of colorectal, lung, and prostate cancers. However, observational studies often overestimate the size of the effect and do not prove causality. This systematic review and meta analysis of pooled data from randomized controlled trials was conducted to evaluate the possible effect of omega 3 fatty acid supplementation on cancer incidence, nonvascular death, and total mortality. The results of our meta analysis suggest that omega 3 fatty acid supplementation has no effect on the incidence of cancer, nonvascular death, and total mortality. Them ain findings are inconsistent with the findings of previous epidemiologic research, and concluded that omega 3 fatty acid supplementation had no significant benefit or adverse effect on the risk of cancer incidence, nonvascular death or total mortality. The reason for this could be that observational studies may overestimate the effect of omega 3 supplementation. There was no significant difference between omega 3 fatty acid supplementation and the placebo for the relative risk of cancer incidence. Omega 3 fatty acids do not seem to affect a mechanism of cancer development that is common across the different types of cancers evaluated in this study. According to this study, omega 3 fatty acid supplementation resulted in a 10 per cent increase in the risk of cancer incidence, but this difference was not statistically significant. The possible reasons for this lack of significant effect are as follows: the use of background omega 3 fatty acid supplementation might have impaired our ability to identify a treatment effect, and trials included were designed to evaluate the effects of omega 3 fatty acid supplementation on cardiovascular outcomes, but not cancer related outcomes, these results were derived from very few cases and should be regarded as preliminary results. Furthermore, high intake of omega 3 fatty acid might stimulate carcinogenesis by increasing oxidative DNA damage. Finally, studies with an open, controlled design may have introduced behavioral differences which may have had an impact on the development of cancer. Therefore, although omega 3 fatty acid supplementation may have direct effects on cancer incidence, these effects may be balanced. Furthermore, subgroup analysis also supports that omega 3 fatty acid supplementation does not affect cancer incidence.
Omega 3 fatty acid supplementation reduced the risk of total mortality only when trials published before 2000, the sample size was less than 1000, the proportion of men in the population was more than 80 per cent or participants received alpha linolenic acid were included. The reason for these findings could be that several factors might affect the efficacy of treatment, which happened to occur more frequently in male patients, such as smoking status.The findings of this study suggest that omega 3 fatty acid supplementation has no significant effects on cancer incidence, nonvascular death, or total mortality. Future studies should focus on healthy individuals to analyze the primary prevention of cancer incidence. We suggest that ongoing trials should be improved in the following ways: any specific type of cancer and total cancer incidents should be recorded and reported normatively, and it should be evaluated in any future trial, and the role of intervention duration and dosage of supplementation should be taken into consideration before evaluating clinical outcomes. (Editors comments)
Omega 3 fatty acid supplementation has been suggested to reduce the risk of cancer incidence, including that of colorectal, lung, and prostate cancers. However, observational studies often overestimate the size of the effect and do not prove causality. This systematic review and meta analysis of pooled data from randomized controlled trials was conducted to evaluate the possible effect of omega 3 fatty acid supplementation on cancer incidence, nonvascular death, and total mortality. The results of our meta analysis suggest that omega 3 fatty acid supplementation has no effect on the incidence of cancer, nonvascular death, and total mortality. Them ain findings are inconsistent with the findings of previous epidemiologic research, and concluded that omega 3 fatty acid supplementation had no significant benefit or adverse effect on the risk of cancer incidence, nonvascular death or total mortality. The reason for this could be that observational studies may overestimate the effect of omega 3 supplementation. There was no significant difference between omega 3 fatty acid supplementation and the placebo for the relative risk of cancer incidence. Omega 3 fatty acids do not seem to affect a mechanism of cancer development that is common across the different types of cancers evaluated in this study. According to this study, omega 3 fatty acid supplementation resulted in a 10 per cent increase in the risk of cancer incidence, but this difference was not statistically significant. The possible reasons for this lack of significant effect are as follows: the use of background omega 3 fatty acid supplementation might have impaired our ability to identify a treatment effect, and trials included were designed to evaluate the effects of omega 3 fatty acid supplementation on cardiovascular outcomes, but not cancer related outcomes, these results were derived from very few cases and should be regarded as preliminary results. Furthermore, high intake of omega 3 fatty acid might stimulate carcinogenesis by increasing oxidative DNA damage. Finally, studies with an open, controlled design may have introduced behavioral differences which may have had an impact on the development of cancer. Therefore, although omega 3 fatty acid supplementation may have direct effects on cancer incidence, these effects may be balanced. Furthermore, subgroup analysis also supports that omega 3 fatty acid supplementation does not affect cancer incidence.
Omega 3 fatty acid supplementation reduced the risk of total mortality only when trials published before 2000, the sample size was less than 1000, the proportion of men in the population was more than 80 per cent or participants received alpha linolenic acid were included. The reason for these findings could be that several factors might affect the efficacy of treatment, which happened to occur more frequently in male patients, such as smoking status.The findings of this study suggest that omega 3 fatty acid supplementation has no significant effects on cancer incidence, nonvascular death, or total mortality. Future studies should focus on healthy individuals to analyze the primary prevention of cancer incidence. We suggest that ongoing trials should be improved in the following ways: any specific type of cancer and total cancer incidents should be recorded and reported normatively, and it should be evaluated in any future trial, and the role of intervention duration and dosage of supplementation should be taken into consideration before evaluating clinical outcomes. (Editors comments)
