Effect of alpha linolenic acid on cardiovascular risk markers: a systematic review

Objective: To determine whether dietary supplementation with a linolenic acid (ALA) can modify established and emerging cardiovascular risk markers. Design: Systematic review and meta-analysis of randomised controlled trials identified by a search of Medline, Embase, Cochrane Controlled Trials Register (CENTRAL), and the metaRegister of Controlled Trials (mRCT). Patients: All human studies were reviewed. Main outcome measures: Changes in concentrations of total cholesterol, low density lipoprotein (LDL) cholesterol, high density lipoprotein (HDL) cholesterol, very low density lipoprotein (VLDL) cholesterol, triglyceride, fibrinogen, and fasting plasma glucose, and changes in body mass index, weight, and systolic and diastolic blood pressure. Results: 14 studies with minimum treatment duration of four weeks were reviewed. ALA had a significant effect on three of the 32 outcomes examined in these studies. Concentrations of fibrinogen (0.17 mmol/l, 95% confidence interval (CI) 20.30 to 20.04, p = 0.01) and fasting plasma glucose (0.20 mmol/l, 95% CI 20.30 to 20.10, p< 0.01) were reduced. There was a small but clinically unimportant decrease in HDL (0.01 mmol/l, 95% CI 20.02 to 0.00, p<0.01). Treatment with ALA did not significantly modify total cholesterol, triglycerides, weight, body mass index, LDL, diastolic blood pressure, systolic blood pressure, VLDL, and apolipoprotein B. Conclusions: Although ALA supplementation may cause small decreases in fibrinogen concentrations and fasting plasma glucose, most cardiovascular risk markers do not appear to be affected. Further trials are needed, but dietary supplementation with ALA to reduce cardiovascular disease cannot be recommended. (Author�s abstract)
The cardiovascular benefits of alpha-linolenic acid (ALA) remain controversial. This was a systematic review of randomised controlled trials conducted to investigate the impact of ALA on cardiovascular risk markers. The data indicates that ALA significantly affects the proinflammatory fibrinogen and fasting plasma glucose concentrations, decreasing fibrinogen concentrations by 0.17 mmol/l and fasting glucose by 0.20 mmol/l. On the basis of estimates from a meta-analysis of observational studies, a 2.9 mmol/l reduction in fibrinogen concentration would lead to a relative risk reduction of 80% in coronary heart disease. A reduction of 0.17 mmol/l attributable to ALA would be expected to lead to a reduction of 6% in coronary heart disease. No other statistically or clinically significant findings were evident in the quantitatively evaluated cardiovascular risk markers. A limitation of the meta-analysis was that most trials were small; they did not describe the method of randomisation and not all of them were blinded. For some potential risk markers the authors were unable to identify two or more studies to allow pooling. Further trials are needed but on the basis of this meta-analysis, dietary supplementation with ALA to reduce cardiovascular disease cannot be recommended. (Editor�s comments)