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Lower blood pressure with DHA, garlic and vitamin C

The omega-3 fat docosahexaenoic acid (DHA), garlic and the antioxidant vitamin C lowered blood pressure in two new studies.

In the DHA study, published in the April 2007 issue of the Journal of Nutrition, researchers from King’s College, London, recruited 38 healthy men and women aged 40 to 65 with normal weight (average body mass index 24) and blood pressure (average 121/79 mmHg). For the first three months, participants took a 1,500 mg capsule that contained 700 mg of DHA or a 1,500 mg capsule containing an olive oil placebo per day.

After a four-month non-treatment (wash-out) period, participants switched treatment and placebo and continued for another three months. The study was double-blind, meaning neither doctors nor participants knew who was taking treatment or placebo.

At the end of the study, compared to placebo, the DHA group had 58% higher DHA levels in the red blood cells and an average decrease in resting-phase (diastolic) blood pressure of 3.3 mmHg to 121/76 mmHg. Heart rates averaged 2.1 fewer beats per minute after DHA than after placebo.

In the garlic-vitamin C study, researchers gave a series of treatments to six subjects with marginally high blood pressure (average 140/90 mmHg). All six participants took a placebo for the first 10 days, followed by a one-week wash-out period. Researchers then gave 2,000 mg of vitamin C per day for 10 days and found no change in blood pressure. After another one-week wash-out period, doctors gave 650 mg of garlic bulb extract powder per day for 10 days and found a significant decrease in contracting-phase (systolic) blood pressure, but not in diastolic pressure.

After a final one-week wash-out period, scientists gave 2,000 mg of vitamin C and 650 mg of garlic per day for 10 days and found that the average systolic and diastolic blood pressure range decreased to 110-120/70-80 mmHg.

In a second, test-tube phase of the study, doctors theorized that garlic and vitamin C might lower blood pressure by increasing nitric oxide (NO), a molecule that occurs in special blood vessel cells (endothelial cells) and is responsible for signaling the muscles surrounding blood vessels to relax. Using endothelial cells, scientists administered garlic and found a twofold increase in NO. After administering garlic and vitamin C together, doctors observed a threefold increase in NO.

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