You’ve probably heard me speak of something called a meta- analysis before, and for those who don’t know what this is, it’s basically a research study that looks at all of the existing research on a subject area e.g. whey protein and muscle growth, and looks at the findings from all of the studies. The researchers look at all of the findings and establish an overall consensus on the benefit of protein and muscle growth (to use the above example). It is therefore widely accepted that if a meta- analysis say’s ‘whey protein supports muscle growth’, then you can say beyond any reasonable doubt, that it does.
Flaxseed and blood pressure
In a new meta- analysis by Ursoniu, Sahebkar and Andrica et al. (2015), the potential of flaxseed to effectively manage blood pressure based on 15 clinical trials, is very strong. The study looked at data from 1,302 participants which indicated that flaxseed supplements are associated with significant reductions in systolic and diastolic blood pressure of 2.85 mmHg and 2.39 mmHg respectively. This is a reasonably high drop and was seen to occur within approx. 12 weeks, but with this said, the researchers also found that flaxseed supplementation in excess of 12 weeks actually resulted in even greater reductions in systolic and diastolic blood pressure. More than 12 weeks of flaxseed supplementation saw a reduction in systolic and diastolic blood pressure of 3.10 mmHg and 2.62 mmHg respectively.
Why does flaxseed help?
Flaxseed contains several bioactive compounds with one of the main ones being lignan, specifically SDG. SDG is a lignan which is known to be an angiotensin- converting enzyme inhibitor (ACE inhibitor). ACE inhibitors inhibit the conversion of angiotensin I to angiotensin II, which is a potent vasoconstrictor. Vasoconstriction causes the blood vessels to become narrower, in turn increasing blood pressure, so by inhibiting the conversion of angiotensin I to angiotensin II you are widening the blood vessels and reducing blood pressure.
Although this theory does make sense, the exact mechanism of action isn’t certain, but other potential benefits could stem from flaxseeds ALA content, ALA is a potent antioxidant and could positively affect blood pressure by its ability to reduce soluble epoxide hydrolase. According to nutraingredients.com (2015), ALA may reduce the inflammatory effects of epoxide hydrolase which would reduce vasoconstriction (narrowing of the arteries), in turn reducing blood pressure.
Although the findings were strong, it worth noting that flaxseed powder was seen to reduce systolic and diastolic blood pressure, whereas flaxseed oil only reduced diastolic blood pressure. However these differences could be for a number of reasons including varied supplement quality, the quantity of fibres in the supplement, and effects on bile acid metabolism, according to the researchers.
So although the evidence is interesting a strong, there is much room for further well- controlled studies to look into the actual quantities of flaxseed needed in people with high blood pressure.
Flaxseed supplements linked to improved blood pressure: Meta-analysis
By Stephen DANIELLS, 09-Jun-2015
Supplements of flaxseed may effectively management blood pressure, says a new meta-analysis of 15 clinical trials.