GARLIC IS is one of the best-selling dietary supplements around the world, and is by far the most popular herb used by patients with cardiovascular disease (CVD). This term covers many heart-related conditions, including high blood pressure, coronary heart disease, heart failure and stroke.
Diet and lifestyle are important in preventing CVD, and garlic is thought to be particularly beneficial. Garlic's reputation is ancient, with references to it being good for the heart and blood in ancient medical texts from India, Egypt, Greece and Rome.
Athletes in the ancient Olympics reportedly consumed large amounts of garlic to increase their stamina. Was this the earliest form of blood-doping?
Garlic has been recommended for many conditions, but only its cardiac effects will be examined here.
Study hard
Evidence from studies in the 1960s noted reduced cholesterol and lipid levels in people taking large amounts of garlic (seven to 28 cloves a day). Whatever the health effects, this amount of raw garlic has serious implications for one's relationships.
Many different products were developed to overcome garlic's odour problem, but the same compounds responsible for the taste and odour seem to be responsible for effects on the heart. A study published at the end of 2007 may explain why.
Garlic has sulphur- containing compounds which, in red blood cells, produce hydrogen sulfide. Better known for its rotten-egg smell, this chemical has recently been shown to play a role in decreasing blood pressure, protecting blood vessels against damage, and acting as an antioxidant.
Such experiments show how garlic could reduce the risk of cardiovascular disease. Clinical studies add more support. Several have shown that garlic has beneficial effects on blood clotting mechanisms. Others show it has antioxidant effects, which can protect blood vessels against damage that could lead to hardening of the arteries.
However, garlic does not always live up to its reputation. Studies in the 1990s reported that garlic reduced cholesterol levels modestly (to a much smaller degree than the widely used statin drugs).
In the last few years, several higher quality studies did not find this benefit. Similarly, early studies reported that garlic lowered blood pressure, but more recent research found garlic no better than a placebo.
Problematic aspects
Garlic is available in many different forms: raw cloves or capsules containing dried garlic powder, aged garlic extract or garlic oil. This makes it difficult to know how much of the active ingredients are in any particular product.
When buying herbal remedies, there is no easy way to know which products are better than others without doing a good deal of background investigation.
Garlic is relatively safe to take, but it can cause intestinal problems and some people are allergic to it. If you react badly to garlic in food, you probably will to the supplements also.
Anyone with a bleeding problem or taking a blood-thinning agent should get medical advice before taking garlic.
Other drugs may interact with garlic, so always discuss herbal remedies you are considering with your doctor or pharmacist.
Recommendations
Overall, garlic can act as a complementary agent in reducing some risk factors associated with cardiovascular disease.
The effect is not large, and in some areas the evidence does not support garlic's reputation.
Given its long tradition of use, and relative safety, garlic can be recommended as part of a heart-healthy diet.
Usually, one fresh clove a day, or 600 to 900 mg dried garlic extract daily, is recommended, but products vary immensely.
Garlic should not be used instead of effective treatments for any heart condition.
Dónal O'Mathúna has a PhD in pharmacy and an MA in bioethics, and is a senior lecturer in the School of Nursing, Dublin City University. He is the author of Alternative Medicine: The Christian Handbook (Zondervan, 2007)