Researchers conducted a review of 46 previously published studies on cardiovascular disease (CVD) involving omega-3 fatty acid consumption. After careful review of the collective data, researchers concluded that increased omega-3 consumption from fish or fish oil supplements, but not alpha linolenic acid (ALA) from foods such as flax, reduces the risk of all-cause mortality, cardiac and sudden death, and possibly stroke.
Although significant benefits were observed in both, the primary-prevention (prevention of a first-time cardiovascular event such as heart attack or stroke) and secondary-prevention (prevention of a second or greater cardiovascular event) groups, the evidence for secondary prevention is much stronger. There was no high-quality data to support a benefit of ALA consumption for CVD risk reduction.
"n-3 Fatty acids from fish oil fish-oil supplements, but not a-linolenic acid, benefit cardiovascular disease outcomes in primary- and secondary-prevention studies: a systematic review." Am. J. Clin. Nutr. 2006; 84:5-17.