For the Most Part, Dietary Supplements Do Not Prevent Cognitive Decline

Americans spend over $25 billion each year on dietary supplements that promise everything from slender waistlines to better sex lives. A large and growing portion of this market is devoted to products that claim to improve memory or prevent the onset of dementia and Alzheimer's disease.

But as researchers investigate these substances to see if there is merit to the claims, they are, by and large, coming up empty-handed. Ginkgo biloba, perhaps the most well known of the "memory enhancers," has been declared ineffective by medical experts based on recent, high-profile studies. And the most encouraging news on other supplements is that more research is needed before they can be recommended and deemed beneficial.

That means there isn't enough reason to try any of these products at this point to ward off cognitive decline. Following are the most current findings on the spectrum of purported memory supplements.

Curcumin & Dementia

This supplement is derived from the Curcuma longa plant, a member of the ginger family. Turmeric, the primary spice in curry, is made from the root of this plant. Laboratory research shows that curcumin has antioxidant and anti-inflammatory properties; antioxidants protect against the damaging effects of free radicals, which are associated with age-related disorders like heart disease and dementia.

Curcumin also might help to reduce the accumulation in the brain of beta-amyloid, the distinguishing plaques of Alzheimer's. Several ongoing studies in humans are currently examining the effects of curcumin on Alzheimer's disease, dementia, and other conditions, but no data are yet available.

Fish Oil & Dementia

Fish oil contains omega-3 fatty acids like docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), which are also found in fatty fish like sardines, lake trout, albacore tuna, flounder, and salmon.

Observational studies suggest a link between diets high in omega-3 fatty acids and a reduced risk of cognitive decline and Alzheimer's disease, possibly owing to the anti-inflammatory and antiamyloid effects of fish oil.

However, a 2008 randomized, controlled trial found that after 26 weeks of supplementation, regular use of DHA and EPA had no effect on cognitive skills compared with a placebo. Additional long-term, well-designed studies are still needed, since the existing studies don't help assess prevention.

Ginkgo Biloba & Dementia

This herbal supplement, extracted from the dried leaves of the ginkgo tree, has antioxidant and anti-amyloid properties. It has been used around the world for centuries to treat a number of conditions.

A 1997 study found improved cognitive functioning in people with Alzheimer's who took ginkgo, but the effect was modest (people who took ginkgo could answer one more question correctly than those who hadn't) and more recent evidence does not back up that early finding.

In 2008, a large randomized, controlled trial found that ginkgo had no preventive effect against dementia or Alzheimer's in more than 3,000 people over age 75 with no memory loss or with mild cognitive impairment; a 2009 follow-up study confirmed those results.

Huperzine A & Dementia

Derived from the plant known as Chinese club moss, Huperzine A (or Hup A) is theorized to be a natural cholinesterase inhibitor, the most effective main class of drug used to treat Alzheimer's by slowing the breakdown of the chemical acetylcholine, which helps form new memories. Hup A may also have antioxidant properties.

The few clinical trials of Hup A as a treatment for dementia have been small studies conducted in China. These results show some promise, and larger studies of Hup A have started in the United States. The results have not yet been published.

Resveratrol, Grape Seed Extract & Dementia

Resveratrol is a type of polyphenol, a plant-based compound with antioxidant properties. Found in grape seeds, grape skins, red grape juice, and red wine, it's being researched because many studies suggest that moderate intake of red wine has a possible role in longevity, heart disease, and cancer prevention and treatment.

Some evidence suggests that resveratrol might decrease levels of beta-amyloid in cells, but this is based mostly on preliminary studies in animals. Clinical trials in humans have yet to be conducted.

Vitamin B6, Vitamin B12, Folic Acid & Dementia

These three B vitamins play an important role in lowering blood levels of the amino acid homocysteine. Elevated levels of homocysteine are associated with several disorders including strokes, heart attacks, cognitive decline, and Alzheimer's disease.

A 2007 study found that total folic acid intake from supplements and diet—but not from vitamin B6 or B12—might reduce the risk of developing Alzheimer's. More recent studies found that supplements containing these nutrients had no effect on cognitive functioning, dementia, or Alzheimer's, though long-term use of folic acid supplements might help the cognitive functioning of older people with high levels of homocysteine.

Vitamins C and E & Dementia

Vitamins C and E are antioxidants, and a handful of earlier, observational studies found that these vitamins might protect against cognitive decline, vascular dementia, and Alzheimer's disease. However, the results of several later investigations have been less promising.

One study found that vitamin E supplements showed no benefit to patients with mild cognitive impairment, and another determined that vitamins C and E did not reduce the risk of dementia among men taking the supplements for short or long periods of time.

Supplements & Dementia: The Bottom Line

Besides the supplements listed above, many more are marketed for their alleged ability to boost memory or cognitive functioning, including phosphatidylserine (PS), choline, bacopa, vinpocetine, piracetam, lemon balm, and coenzyme Q10 (CoQ10). However, the reality is that these supplements have not been studied extensively, or they have shown little potential.

Part of the problem is that the U.S. Food and Drug Administration (FDA) doesn't require supplements to be tested to the same degree as prescription drugs.

Remember that there is no "silver bullet" that will undo bad habits, so continue to follow the fundamentals of good health: Exercise, do not smoke, and eat a well-balanced, nutritious diet. If you have high blood pressure, elevated cholesterol levels, or diabetes, make sure you get them adequately treated.

And if you do decide to take any kind of supplement, always remember to use caution and inform your doctor. Supplements can worsen certain health problems and interact with prescription and over-the-counter drugs to cause severe side effects or render your medication less effective.

Publication Review By: Peter V. Rabins, M.D., M.P.H.

Published: 15 Mar 2011

Last Modified: 01 Dec 2014