I was surprised to see a chapter in Fish, Omega-3 and Human Health devoted to hypertension. Isn’t high blood pressure caused by too much salt and too much weight? Well, yes, but a special strain of rats used as an animal model of hypertension turned out to have a defect in their immune system. Perhaps high blood pressure is also caused by immune-system over-reaction.
A 1993 meta-analysis of studies of the effect of fish oil on blood pressure concluded:
Diet supplementation with a relatively high dose of omega-3 PUFA, generally more than 3 g/d, can lead to clinically relevant BP reductions in individuals with untreated hypertension.
The sizes of the blood pressure changes:
Weighted, pooled estimates of SBP [systolic blood pressure] and DBP [diastolic blood pressure] change (mm Hg) with 95% confidence intervals were -1.0 (-2.0 to 0.0) and -0.5 (-1.2 to +0.2) in the trials of normotensives, and -5.5 (-8.1 to -2.9) and -3.5 (-5.0 to -2.1) in the trials of untreated hypertensives.
A different meta-analysis reached essentially the same conclusion.
Note the use of fish oil. Fish oil has long-chain omega-3 fats, while flaxseed oil — which I have used in my self-experimentation — has only the short-chain omega-3 fat, which is converted to long-chain omega-3 after you eat it. Fish oil is often considered better because the omega-3s don’t need to be converted. But this way of thinking misses something. Because the omega-3s in flaxseed oil are converted to long-chain omega-3s by enzymes, the amount of long-chain omega-3 in the body rises more slowly (and thus lasts longer) than if you take fish oil supplying the same amount of long-chain omega-3. Flaxseed oil supplies a kind of time-release long-chain omega-3. A long low dose could easily be more potent than a short high dose.
Thanks to Dave Lull.