Although there is a growing body of studies (animal, observational and clinical) suggesting that omega-3 fatty acids supplements, fibre supplements, calcium, magnesium, and vitamin C are associated with lower BP, the AHA claims that the current data are insufficient or unclear.
Hypertension, defined as having a systolic and diastolic BP greater than 140 and 90 mmHg, affects about 600 million people worldwide and is associated with over seven million deaths. Estimates indicate 27 per cent of the US adult population is hypertensive.
Studies have shown that lowering blood pressure slightly could have profound implications for health: it is thought that a mere three mmHg drop in systolic BP across in those with hypertension may translate into an eight per cent reduction in stroke mortality in the population as a whole, and a five per cent drop in deaths from coronary heart disease.
Losing weight, cutting back on salt intake, and drinking less alcohol are well established as a means to lower blood pressure, and the AHA is very much in favour of measures incorporated into the everyday diet, rather than dietary supplements.
In the scientific statement, published in the February issue of the journal Hypertension (Vol. 47, pp. 296-308), the AHA recommended increased potassium intake as a key hypertension preventative "because a high potassium intake can be achieved through diet rather than pills, the preferred strategy to increase potassium intake is to consume foods such as fruits and vegetables that are rich in potassium, rather than supplements."
Clinical trials for omega-3 fatty acids have reported BP reductions in people with hypertension, but the effect appeared to be dose dependent and relatively high (greater than three grams per day). At such doses side effects like belching and a fishy taste were recorded, which discouraged the AHA from recommending omega-3 supplements.
The British Heart Foundation, on the other hand, recommends eating oily fish at least twice a week "to reduce the risk of coronary heart disease and to improve the chances of survival after a heart attack."
Results from studies involving fibre, calcium or magnesium supplements appear inconclusive with observational studies reporting positive associations while small clinical trials reported no link.
Similar inconsistencies were reported for vitamin C observation studies and clinical trials.
While the evidence may be insufficient or unclear for these supplements for lowering BP, no reports were mentioned that suggest they could increase BP, which is good news for many consumers taking supplements of omega-3, vitamin C, or magnesium for other health reasons.
"A substantial body of evidence strongly supports the concept that multiple dietary factors affect BP. Dietary modifications that effectively lower BP are weight loss, reduced salt intake, increased potassium intake, and consumption of an overall healthy diet," said the statement.
"Other dietary factors may also affect BP, but the effects are small and/or the evidence is uncertain."
Dr John Hathcock, vice president, scientific & international affairs from the Council for Responsible Nutrition (CRN), stressed that the conclusions drawn in the review concerning supplements should not be over-interpreted.
Hathcock told NutraIngredients-USA.com: "For omega-3 there is clearly an important effect which could support omega-3 supplements. However, the effects of omega-3 are clearly not large enough to be dependable on their own to reduce hypertension."
Both calcium and vitamin C had clear and important effects, according to Hathcock, but again no one should think of taking a supplement of either in the belief that it would reduce their blood pressure.
"For potassium, the levels required could not be taken by supplementation. It is a cause and effect situation for potassium since high potassium diets tend to be low sodium diets, which have been shown to help people with hypertension," he said.