A combination of garlic supplements and vitamin C reduced blood pressure back to normal levels in people with mildly elevated levels, says a pilot study.
"Combinations of garlic and vitamin C are an effective alternative in the control of marginally high blood pressure," wrote authors Adam Mousa and Shaker Mousa in the journal Nutrition Research (Elsevier).
"Garlic ingredients or garlic extract alone increased endothelial cell NO production, an effect that was shown to be enhanced by the combination with antioxidant vitamins," they said.
The study adds to a large body of science indicating cardiovascular benefits for garlic, with consumer awareness of potential health benefits already high. This has benefited the supplements industry, particularly since consumers seek the benefits of garlic without the odours that accompany the fresh bulb.
Garlic supplements are worth more than $100m (€79.5m) in the US and are also one of the biggest sellers in the UK market. According to a 1998 survey by Hartman and New Hope, garlic supplements are used twice as much as other herbal supplements.
Mousa and Mousa recruited six subjects with marginally elevated blood pressure (140/90 mmHg) and assigned them to take placebo for 10 days; followed by one-week washout, then vitamin C (2000 mg) for 10 days, a further week of wash-out period, then garlic tablets (650 mg of bulb powder) for 10 days. Finally, after the last washout, garlic and vitamin C were given together for 10 days.
They report that the daily vitamin C alone did not have any effect on blood pressure, while garlic alone resulted in a significant decrease in systolic but not diastolic blood pressure. When the supplements were given together mean systolic and diastolic blood pressures reduced to reference values of 110-120 and 75-80 mmHg, respectively. Blood pressure increased when the combined supplement was stopped.
The mechanism behind the apparent effects was proposed to be due to effects of garlic on the production of nitric oxide (NO) in endothelium cells (cells that line the walls of blood vessels). NO is a molecule used by the endothelium to signal surrounding muscle to relax, thereby dilating the blood vessels and increasing blood flow.
Indeed, measurements of NO levels after garlic administration showed a two-fold increase, relative to placebo, while administration of both garlic and vitamin C resulted in a three-fold increase, relative to the control.
"The effects of garlic and its combination with antioxidants on blood pressure might be explained on the basis of the cellular effects on NO production," wrote the researchers.
Further studies are needed to confirm these results, with larger study populations and longer intervention periods necessary.
A recent trial, published in the Archives of Internal Medicine, reported that garlic, both raw and from supplements, had no effect on the cholesterol levels of 192 adults with slightly elevated cholesterol levels (hypercholesterolaemia).
Source: Nutrition Research
Volume 27, Issue 2, Pages 119-123
"Cellular effects of garlic supplements and antioxidant vitamins in lowering marginally high blood pressure in humans: pilot study"
Authors: A.S. Mousa and S.A. Mousa