High blood pressure is a risk factor for cardiovascular disease. Blood pressure rises with weight gain and one of the most effective ways to control blood pressure is to lose excess body fat. The cause of blood pressure is complex, but increasingly endothelial dysfunction is being linked to its aetiology. Endothelial dysfunction is a condition whereby the vasculature of the body loses some of its ability to relax in response to blood flow, a process called flow mediated dilation. This results in an increase in diastolic blood pressure. The cause of endothelial dysfunction has been extensively investigated and may involve a deficiency of the enzyme nitric oxide synthase in the endothelial cells of the vasculature. This enzyme synthesises nitric oxide, the chemical responsible for signalling the vasculature to dilate through a relaxatory influence on its skeletal muscle. Nitric oxide synthase may be affected negatively by free radicals, which inhibit the enzyme and prevent the synthesis of nitric oxide.
The high antioxidant content of plant foods may explain their blood pressure lowering effects. A number of plant foods have been shown to lower blood pressure, and generally plant based diets are protective of cardiovascular disease. A number of studies have shown blood pressure lowering effects for flaxseeds and recently a meta-analysis was performed to estimate the degree of blood pressure lowering effects seen with flaxseed consumption. Researchers1 calculated that flaxseed supplementation resulted in a reduction in systolic blood pressure that equated to about 1.77 mmHg and a reduction in diastolic blood pressure that equated to about 1.58 mmHg. Subgroup analysis showed that subjects consuming whole flaxseeds experienced a 1.93 mmHg reduction in blood pressure when consumption was equal to 12 weeks. Therefore the effects of flaxseed may be greater when the whole seed is consumed (rather than the oil) suggesting that compounds in the seeds, perhaps antioxidants, are responsible for the effect.
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