Dietary alpha-Linolenic Acid Is Associated with Reduced Risk of Fatal Coronary Heart Disease, but Increased Prostate Cancer Risk: A Meta-Analysis
Dietary alpha-Linolenic Acid Is Associated with Reduced Risk of Fatal Coronary Heart Disease, but Increased Prostate Cancer Risk: A Meta-Analysis
Year: 2004
Authors: Brouwer, I.A. Katan, M.B. Zock, P.L.
Publication Name: J. Nutr.
Publication Details: Volume 134:; Pages 919 – 922.
Abstract:
The objective of this meta-analysis was to estimate quantitatively the associations between intake of α-linolenic acid [ALA, the (n-3) fatty acid in vegetable oils], mortality from heart disease, and the occurrence of prostate cancer in observational studies. We identified 5 prospective cohort studies that reported intake of ALA and mortality from heart disease. We also reviewed data from 3 clinical trials on ALA intake and heart disease. In addition, we identified 9 cohort and case-control studies that reported on the association between ALA intake or blood levels and incidence or prevalence of prostate cancer. We combined risk estimates across studies using a random-effects model. High ALA intake was associated with reduced risk of fatal heart disease in prospective cohort studies (combined relative risk 0.79, 95% CI 0.60�1.04). Three open-label trials also indicated that ALA may protect against heart disease. However, epidemiologic studies also showed an increased risk of prostate cancer in men with a high intake or blood level of ALA (combined relative risk 1.70; 95% CI 1.12�2.58). This meta-analysis shows that consumption of ALA might reduce heart disease mortality. However, the association between high intake of ALA and prostate cancer is of concern and warrants further study. (Author�s abstract)
Dietary ALA occurs mainly in plants and vegetable oils; its intake in affluent countries is 5�10 times higher than that of (n-3) fatty acids from fish. The outcome of this meta-analysis of prospective studies taken together with the results of the clinical trials suggests that an increased intake of ALA can lower the risk of fatal coronary heart disease. The most likely mechanism by which ALA may prevent fatal heart disease is by reducing cardiac arrhythmia. In this study, there were also indications for an increased risk of prostate cancer in men with a high intake of ALA compared with those with a low intake. Subsequent research suggests however that the relationship may be spurious and confounded by advanced disease states and levels of saturated fat in the diet. However the authors do suggest that the protective effect of ALA on fatal coronary heart disease would probably outweigh any possible negative effects, especially for men with an increased risk of heart disease. In some countries, meat and not vegetable oil is the major source of ALA, and the apparently deleterious effect of ALA could therefore be caused by high meat intake instead of high ALA intake. This would lead to an increased risk of prostate cancer in those studies in which meat was the major source of ALA and not in those studies in which vegetable oils were the major source of ALA. ALA could provide an alternative for those subjects who are at high risk of cardiovascular disease and who, for various reasons, do not want to consume fish. Another advantage of increased use of ALA instead of (n-3) fatty acids from fish would be the lower burden on the environment. Use of ALA instead of fish fatty acids could help to prevent depletion of the oceans from certain fish species. ALA consumption might have a substantial effect on heart disease mortality, but the positive association between intake of ALA and prostate cancer is of concern and requires further study. Double-blind, randomized clinical trials are required to provide definitive answers on ALA intake and heart disease. Such trials will lack the power to detect effects of ALA intake on prostate cancer, but studies of prostate-specific antigen may provide a surrogate marker. (Editor�s comments)
Dietary ALA occurs mainly in plants and vegetable oils; its intake in affluent countries is 5�10 times higher than that of (n-3) fatty acids from fish. The outcome of this meta-analysis of prospective studies taken together with the results of the clinical trials suggests that an increased intake of ALA can lower the risk of fatal coronary heart disease. The most likely mechanism by which ALA may prevent fatal heart disease is by reducing cardiac arrhythmia. In this study, there were also indications for an increased risk of prostate cancer in men with a high intake of ALA compared with those with a low intake. Subsequent research suggests however that the relationship may be spurious and confounded by advanced disease states and levels of saturated fat in the diet. However the authors do suggest that the protective effect of ALA on fatal coronary heart disease would probably outweigh any possible negative effects, especially for men with an increased risk of heart disease. In some countries, meat and not vegetable oil is the major source of ALA, and the apparently deleterious effect of ALA could therefore be caused by high meat intake instead of high ALA intake. This would lead to an increased risk of prostate cancer in those studies in which meat was the major source of ALA and not in those studies in which vegetable oils were the major source of ALA. ALA could provide an alternative for those subjects who are at high risk of cardiovascular disease and who, for various reasons, do not want to consume fish. Another advantage of increased use of ALA instead of (n-3) fatty acids from fish would be the lower burden on the environment. Use of ALA instead of fish fatty acids could help to prevent depletion of the oceans from certain fish species. ALA consumption might have a substantial effect on heart disease mortality, but the positive association between intake of ALA and prostate cancer is of concern and requires further study. Double-blind, randomized clinical trials are required to provide definitive answers on ALA intake and heart disease. Such trials will lack the power to detect effects of ALA intake on prostate cancer, but studies of prostate-specific antigen may provide a surrogate marker. (Editor�s comments)
