Efficacy of Over-the-Counter Nutritional Supplements

Davidson MH, Geohas CT.

Overview More than 100 million people in the US report using nutritional supplements, spending more than $17 billion on these supplements. Most people are under the erroneous impression that all nutritional supplements offer health benefits and are closely regulated to ensure safety and efficacy. Unfortunately, the Dietary Supplement Health and Education Act of 1994 allows for the promotion of nutritional supplements without review by the FDA; therefore, it is important to evaluate the efficacy and safety of these supplements. Nutritional supplements with strong evidence There is strong scientific evidence supporting the use of:

Plant sterols/stanols. Plant sterols inhibit intestinal cholesterol absorption. Plant sterols and stanols put in a fat medium such as margarine have been shown to lower low-density lipoprotein (LDL) by 7% to 14%. One large Finnish study demonstrated that replacing part of the daily fat intake with margarine enriched with plant stanols lowered LDL cholesterol by 14%. This level of reduction is greater than that achieved in outpatients who follow American Heart Association Step I and Step II diets.
Omega-3 fatty acids. Omega-3 (n-3) fatty acids are found predominantly in fatty fish (salmon, tuna, mackerel, sardines, and herring) and fish oils. Many trials have linked fish consumption with a decrease in coronary heart disease (CHD) risk in both primary and secondary prevention trials. The Diet and Reinfarction trial (DART) found a fish diet superior to a high-fiber and low-fat diet in reducing cardiovascular events in patients with CHD. Fish oil concentrates have been found to decrease morbidity and mortality.
Niacin. Nicotinic acid or niacin is a soluble B vitamin that has favorable effects on all of the lipid subfractions. On average, niacin lowers LDL by 10% to 20%, triglycerides by 20% to 40%, and lipoprotein(a) by 10% to 30%, and raises HDL by 15% to 30%. Niacin has been shown to reduce cardiovascular morbidity and mortality. However, the use of niacin is often limited by poor tolerability.
Folate, vitamin B6, and vitamin B12. The normal metabolism of homocysteine requires an adequate supply of folate, vitamin B6, vitamin B12, and riboflavin. Elevated homocysteine levels are a risk factor for cardiovascular disease. A meta-analysis study showed that as much as 10% of coronary artery disease risk was attributed to hyperhomocysteinemia. The most effective therapy for lowering homocysteine is the administration of folate (1 to 2 mg/d).
Tree nuts. Nuts (almonds, cashews, hazelnuts, macadamia nuts, peanuts, pecans, pistachios, and walnuts) have a protective effect against CHD, which is thought to be due to favorable effects on plasma lipids and lipoproteins. Most fats in the nuts are mono- or polyunsaturated fats, which lower LDL cholesterol. Consuming nuts more than once a week (1 oz per serving) reduces the relative risk of CHD in both men and women.

Nutritional supplements with potential evidence There is potential evidence for the health benefits of:

Soy protein. Soy contains isoflavones, which have properties similar to estrogen. A 1995 meta-analysis concluded that consumption of soy protein in place of animal protein lowered total cholesterol by 9.3%, LDL cholesterol by 12.9%, and triglycerides by 10.5% without affecting HDL cholesterol.
Tea extracts/flavonoids. Flavonoids are chemicals found in plants that act as potent antioxidants. They are found in green and black tea and grape juice and wine. There is emerging evidence that tea may reduce the risk of CHD. In one study, intake of catechin (which belongs to the flavonoid family) was inversely associated with ischemic heart disease mortality. In another, one cup of tea per day was associated with a 44% reduction in risk of myocardial infarction compared with that seen in non-tea drinkers. Grape juice has also been shown to reduce LDL oxidation, improve endothelial function, and reduce platelet aggregability.
Policosanol. Policosanol is a mixture of fatty alcohols derived from the wax of honey bees. It reduces cholesterol and platelet aggregation and is believed to inhibit the oxidation of LDL. Efficacy and safety have been proven in a few clinical trials.
Guggulipids/guggul. Guggulu is a botanical extract. Guggul extract isolates ketonic steroid compounds from the plant. Many small studies have shown guggul to lower cholesterol and triglycerides. Guggulipids lower VLDL cholesterol and LDL cholesterol while elevating HDL cholesterol. The mechanism of action is thought to be through the increased liver metabolism of LDL. One study of 61 patients taking guggul 25 mg three times per day showed an 11.7% reduction in total cholesterol, a 12.7% decrease in LDL, and a 12% decrease in triglycerides. Long-term safety has not been established.
Coenzyme Q10. Coenzyme Q10 (ubiquinone) is a potent antioxidant that is produced during the synthesis of cholesterol. In theory, coenzyme Q10 (at 50 to 60 mg/d) may reduce the risk of myopathy. Trials conducted in Europe and Japan support the contention that coenzyme Q10 might improve congestive heart failure. However, in two recent studies, coenzyme Q10 did not improve morbidity or mortality compared with placebo. Currently, the American Heart Association does not recommend using antioxidant vitamin supplementation until more complete data is available.
L-arginine.L-arginine deficiency has been hypothesized as leading to coronary artery disease. Dietary supplements of L-arginine have been shown to improve endothelial function, but most published human studies are small, and better studies are needed before L-arginine can be recommended.

Nutritional supplements with lack of evidence There has been a lack of evidence for the health benefits of:

Vitamin E/antioxidants. In several studies on mice, antioxidants, such as vitamin E, have been effective in reducing atherosclerosis. However, the results of antioxidant trials for the treatment of atherosclerosis and the prevention of CHD have been mixed and mostly disappointing.

Garlic.

Conclusion Study authors call for consumers to make educated decisions about supplement usage. A decision to use supplements should take into account their unregulated nature and whether clinically proven evidence or national guidelines recommend their use to reduce the risk of cardiovascular disease. The full-text of this article can be found at http://www.current-reports.com/1523-3804/5/15. Curr Atheroscler Rep 2003 Jan;5(1):15-21. Return to Top