Background: Hypertension is one of the largest health burdens in the world, leading to stroke, coronary heart disease, myocardial infarct, peripheral artery disease (PAD) and renal failure. There are many pharmaceutical medications on the market for blood pressure management. Many of these medications have undesirable side effects or are expensive. Dietary intervention with omega-3 fatty acids has become a popular alternative to medication for blood pressure (BP) control. The cardiovascular benefits of omega-3 fatty acids consumed via fish oil have been well established. More research is being done to establish the mechanism and efficacy of other dietary sources containing fatty acids. It has been suggested that foods high in alpha-linolenic acid (ALA) may have cardio protective properties. Dietary flaxseed is one of the foods of interest being it contains the highest level of ALA. Although the mechanisms are not fully understood, dietary flaxseed may be an effective and safe alternative for BP management.
Methods: An exhaustive search was conducted using Medline-OVID, CINAHL, and Web of Science using the keywords: flax, flaxseed, linseed oil, blood pressure, and hypertension. Relevant articles were assessed for quality using GRADE. A search on the NIH clinical trials site reveals there is one trial currently registered relating to the antihypertensive effects of dietary flaxseed.
Results: Two studies met the search criteria and were included in this systematic review. The first study, FLAX-PAD, was a double blind, placebo-controlled, randomized controlled study (RCT) utilized to examine the effects of dietary flaxseed on systolic BP and diastolic BP in patients newly diagnosed with PAD. This study demonstrated the antihypertensive effects in patients consuming dietary flaxseed. Researchers also revealed the relationship between plasma ALA levels and blood pressure. The second study was a prospective, two-group, parallel-arm design RCT to examine the effects of dietary flaxseed on blood pressure in middle-aged dyslipidemic men. This study revealed a significant reduction in blood pressure in individuals receiving the intervention.
Conclusion: Daily consumption of 30g of milled flaxseed or 15mL of flax oil per day has shown an antihypertensive effect on select patient populations. The latest studies regarding flaxseed and its antihypertensive effects seem promising, but further randomized controlled trials are needed to clearly establish its efficacy.
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