Flaxseed (Linum usitatissimum) and Cardiovascular / heart health: evidence and sources

Hypertension is the single largest risk factor attributed to mortality in the world. Medications are the primary treatment for hypertension; however, adherence to drug regimens is low (~50 %). Low adherence may be a contributing factor leading to uncontrolled blood pressure in patients. An effective alternative or complement to medications in managing hypertension is through lifestyle modifications. Adopting a healthy diet is a valuable strategy. A recent, randomized controlled year-long trial observed impressive reductions in blood pressure in patients with hypertension consuming flaxseed daily. Therefore, attention has been garnered for flaxseed as a potentially valuable strategy for the management of hypertension. This review will highlight the recent data for flaxseed and its extracts in blood pressure regulation in both animal models and clinical trials. Insight into the proposed anti-hypertensive mechanism of flaxseed and the implications of flaxseed as a potential global anti-hypertensive therapy will be discussed.

Flaxseed is the richest source of the lignan secoisolariciresinol diglucoside (SDG). After ingestion, SDG is converted to secoisolariciresinol, which is further metabolised to the mammalian lignans enterodiol and enterolactone. A growing body of evidence suggests that SDG metabolites may provide health benefits due to their weak oestrogenic or anti-oestrogenic effects, antioxidant activity, ability to induce phase 2 proteins and/or inhibit the activity of certain enzymes, or by mechanisms yet unidentified. Human and animal studies identify the benefits of SDG consumption. SDG metabolites may protect against CVD and the metabolic syndrome by reducing lipid and glucose concentrations, lowering blood pressure, and decreasing oxidative stress and inflammation. Flax lignans may also reduce cancer risk by preventing pre-cancerous cellular changes and by reducing angiogenesis and metastasis. Thus, dietary SDG has the potential to decrease the incidence of several chronic diseases that result in significant morbidity and mortality in industrialised countries. The available literature, though, makes it difficult to clearly identify SDG health effects because of the wide variability in study methods. However, the current evidence suggests that a dose of at least 500 mg SDG/d for approximately 8 weeks is needed to observe positive effects on cardiovascular risk factors in human patients. Flaxseed and its lignan extracts appear to be safe for most adult populations, though animal studies suggest that pregnant women should limit their exposure. The present review discusses the potential health benefits of SDG in humans, with supporting evidence from animal studies, and offers suggestions for future research.