In the UK alone, there are an estimated 10m people with hypertension, defined as having blood pressure higher than 140/90mmHg. The condition is a major risk factor for cardiovascular disease (CVD).
“The magnitude of the hypotensive effect (5mmHG or 3-6 percent) is certainly clinically relevant, and is expected to considerably reduce the overall CVD risk in these patients,” wrote lead author George Paschos in the European Journal of Clinical Nutrition.
How the study was done
The researchers, from Harokopio University and Laiko Hospital in Athens, recruited 59 middle-aged men (average age 53) with abnormal blood lipid levels (dyslipidaemic) and randomly assigned them to receive either the omega-3-ALA-rich flaxseed supplements (8g per day) or omega-6 linoleic acid-rich safflower oil in a prospective, two-group, parallel-arm study.
The ALA-rich diet gave an omega-6 to omega-3 ratio of 1.3:1, while the LA-rich diet gave an omega-6 to omega-3 ratio of 13.2:1.
After 12 weeks of supplementation they report that the men receiving the ALA-rich flaxseed oil supplements were found to have reduced systolic and diastolic blood pressures, falling from 120 to 100mmHg and 80 to 72mmHg, respectively. These falls equated to a decrease in systolic blood pressure of 3,1 percent and diastolic blood pressure of 6,3 percent.
The omega-6-rich LA supplement did not significantly affect blood pressure, said the researchers.
“Our results indicate that increased ALA intake can bring about a significant decrease in SBP and DMP by approximately 5mmHg or 3-6 percent,” wrote the researchers.
Exact mechanism unclear
The mechanism behind the effects is not clear, they said, and may be due to the effect of the omega-3 metabolites, prostaglandins, on a variety of blood pressure regulators, including control of salt and water balance, control of blood flow in the kidneys and effects on heart output.
Future studies are needed, they said, to further clarify the underlying mechanism(s).
The study does have several limitations, said Paschos, the most notable of which being that the dose of flaxseed given is not readily achievable in a conventional diet.
“However, several products like cooking oil, margarine, salad dressing, and mayonnaise fortified with ALA can be produced by the industry, and inclusion of these foods in the diet has been shown to substantially increase dietary ALA intake to levels exceeding those used in the present study,” he wrote.
“Hence we believe our results could be applicable in practice.”
The study was funded by the Greek Ministry of Development, General Secretariat for Research and Technology. - (Decision News Media, February 2007)