Forget about those over-the-counter products that promise better memory.

A recent survey found that about 25% of adults over age 50 take a supplement to improve their brain health with the promise of enhanced memory and sharper attention and focus.

The problem? There's no solid proof any of them work.

"The main issue with all over-the-counter supplements is lack of regulation," says Dr. Gad Marshall, associate medical director at the Center for Alzheimer Research and Treatment at Harvard-affiliated Brigham and Women's Hospital. "The FDA doesn't oversee product testing or ingredient accuracy — they just look out for supplements that make health claims related to the treatment of specific diseases."

In terms of brain health, this means a supplement manufacturer can claim a product helps with mental alertness or memory loss — but not that it protects against or improves dementia or Alzheimer's disease. "This way manufacturers don't have to back up any claim that their product is effective or even safe," says Dr. Marshall.

A combination of nutrients

Many brain supplements focus on omega-3 fatty acids (such as those found in fish oil), vitamin E, various B vitamins, or various combinations. Why these?

There's strong evidence that certain diets — like the Mediterranean diet, the DASH diet, and the MIND diet — can help improve cognitive function, according to Dr. Marshall.

"These diets contain foods with large amounts of these vitamins and minerals," he says. "But what is not clear is whether it's the combination of nutrients in these diets that's beneficial, or whether it's specific ones or even certain amounts, or some other factors." Researchers have tried to answer these questions by testing how these individual nutrients affect cognitive health. So far the limited studies have found no evidence they help, with a few rare exceptions.

"Still, this doesn't mean that the brain supplements may not work," says Dr. Marshall. "It's just that there is not much, if any, evidence from randomized clinical trials — the gold standard for research — on isolated vitamins or minerals and brain health."

Here's a summary of what science has found so far and what it means.

Omega-3 fatty acids (fish oil)

There are three types of omega-3s: eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) — which are found mostly in fatty fish like salmon and mackerel — and alpha-linolenic acid (ALA), which is found in leafy green vegetables (Brussels sprouts, spinach), vegetable oils (canola, soybean), and nuts and seeds (walnuts, flaxseeds).

"The body coverts ALA into EPA or DHA, but only in small amounts, so the best way to get high amounts of EPA and DHA is by eating more fish," says Dr. Marshall.

Omega-3s help build cell membranes in the brain and also may have anti-inflammatory and antioxidant effects that could protect brain cells.

Fish is a staple in the Mediterranean and MIND diets, among others, and studies have found an association between higher intake of fish and a lower risk of cognitive decline. However, omega-3 supplements haven't shown the same effect. "Any benefit seems to come from a greater intake of fish and not from taking fish oil supplements," says Dr. Marshall.

Vitamin E

Vitamin E is an antioxidant and is believed to help with brain health by reducing oxidative stress. It is the only supplement that has been found to have any possible benefit.

A 2014 study in the journal Nutrients reviewed the existing research on vitamin E and various health issues, such as heart disease, stroke, and Alzheimer's disease.

The researchers found that high-dose vitamin E may help people with mild to moderate Alzheimer's dementia continue to perform daily life functions for a short period of time. However, vitamin E does not prevent the disease or reduce other symptoms, and high doses increase the risk of hemorrhagic stroke.

B vitamins

Three B vitamins are often linked with brain health: B 6 , B 9 (folate), and B 12 . They can help break down homocysteine, high levels of which have been associated with a greater risk of dementia and Alzheimer's disease. B vitamins also help produce energy needed to develop new brain cells.

However, most people get enough B vitamins through their diet. "You may need extra B vitamins via supplements if you have a deficiency, or have trouble getting enough through your diet, but otherwise they do not have any clear benefit for brain health," says Dr. Marshall.

What the leaves say about ginkgo biloba The fan-shaped leaves of the ginkgo tree are used in traditional Chinese medicine to treat all kinds of ailments. In the United States, the extract from the leaves is sold as a supplement commonly called ginkgo biloba. One of its main selling points is as a memory enhancer. However, as with other brain health supplements, the science doesn't support the claims. One of the largest clinical trials that explored the possible link was the Ginkgo Evaluation of Memory (GEM) study. Researchers recruited more than 3,000 older adults, average age 79, 54% of whom were men, with normal cognitive function or mild cognitive impairment. Everyone was given either 120 milligrams of ginkgo or a placebo twice a day for almost six years. (This amount was chosen based on previous research.) The results found that ginkgo biloba did not lower the overall rate of developing dementia. "Most supplements are not tested rigorously in clinical trials," says Dr. Gad Marshall, associate medical director at the Center for Alzheimer Research and Treatment at Brigham and Women's Hospital. "However, ginkgo has been tested thoroughly for its potential to prevent dementia, and there is strong evidence that it does not prevent memory decline or dementia and therefore should not be taken for that purpose."

Thinking about supplements

So the question remains: with no evidence, why do people still buy in to brain health supplements? "The idea still exists that it's easier to take a pill than to make lasting lifestyle changes," says Dr. Marshall.

Until more is known, Dr. Marshall's advice is to save your money. "Invest more in doing aerobic exercise and following a plant-based diet. These can help with memory and brain health in the long term more than any supplement."

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