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Uma Naidoo M.D.
Uma Naidoo M.D.

The Pros and Cons of Antioxidant Foods on the Brain

New research helps explain why antioxidants may help or hurt you

Source: Lisovskaya/iStockphoto

Oxidation is a chemical process in the body that releases certain particles known as reactive oxygen species (ROS) that include free radicals, which are any molecules that have an unpaired electron. At low to moderate concentrations, they participate in important physiologic processes in your brain's cells, but at higher concentrations, they can damage brain cells too.

Too much ROS results in what we call oxidative stress, and this may contribute to brain cell loss or damage. The human body is well equipped to deal with oxidative stress. It can prevent cell damage, But in the course of life, if we are exposed to too much oxidative stress through disease, cigarette smoke, ozone exposure, ionizing radiation or heavy metal ions such as iron, mercury, lead or copper, we may need an antioxidant boost, That's when antioxidant foods come in handy. And it's important to understand the subtleties behind this.

Risks of antioxidants: Not all antioxidants are obviously helpful. Antioxidants such as β-carotene (from carrots) or lycopene (from tomatoes) and the vitamins C and E supposedly offer protection against cancer or aging because they diminish or prevent the effects of free radicals. But always diminishing free radical may not be helpful. Free radicals are essential for energy metabolism in the cell as well as the protective function of our neutrophils (a type of white blood cell) against pathogens. We sometimes need them.

Also, under certain conditions, antioxidants behave like the opposites of themselves—they become pro-oxidants. β-carotene and vitamin C are notorious for these effects. In fact, two studies on highly dosed β-carotene supplementation found that β-carotene supplementation increased cancer risk. Even our molecules behave in paradoxical ways!

A thorough and systematic review by the Cochrane Hepatobiliary Group found that in 68 randomized trials with 232,606 participants, “Treatment with beta carotene, vitamin A, and vitamin E may increase mortality. The potential roles of vitamin C and selenium on mortality need further study.”

In the brain, ROS can cause blood vessel and tissue damage leading to cells being deprived of oxygen from less blood perfused tissue. This can damage those cells. But if antioxidants turn into pro-oxidants, this can make this situation worse.

With these facts against antioxidants, we must be careful not to overgeneralize the benefits of antioxidants, of which there appear to be many.

Benefits of antioxidants: In 2016, researchers Nur Adelier and Health Sparks explained that Vitamin E, turmeric and saffron may all Conference protections against Alzheimer's disease (AD) and may even improve survival through their antioxidant effects.

Turmeric is not as homogenous as it sounds. The spice contains over 235 compounds, but among the most bioactive are the curcuminoids. Many studies have shown that it may be beneficial for Alzheimer's disease and it may help cognitive decline, though some point out that we need more evidence for this.

In one double-blind placebo-controlled study, saffron was found to be effective for mild to moderate AD. Others have supported the finding too. And it was safe as well.

When it comes to cognition, findings are similarly conflicted. One long-term study in nurses found that long-term vitamin E and C intakes were not consistently related to cognition, although greater consumption of carotenoids may have cognitive benefits in older adults. Still, another more recent study found that higher vitamin E was associated with a higher score on verbal memory and immediate recall, and better language/verbal fluency performance.

As a result of some of these findings, researchers are now talking about an optimal oxidant/antioxidant balance, and not just the unfettered use of antioxidants in all conditions at any dose.

Other antioxidants or antioxidant-inducing substances or approaches that might improve cognition include soybeans that contain phytoalexins, the ketogenic diet, raisins, and β-cryptoxanthin and zeaxanthin are also antioxidants that are lower in people who are cognitively frail.

Common foods that contain antioxidants: Here is a simple list of foods and ethnic food types that contain some of the antioxidants I mentioned:

β-carotene: Carrots, sweet potatoes, squash, kale, apricots

Vitamin C: Broccoli, Brussels sprouts, tomatoes, oranges, lemons

Vitamin E: Spinach, avocado, almonds, broccoli, sunflower seeds, Atlantic salmon

While the actual lists are much longer, I just wanted you to see many many of these antioxidants come from plants and vegetables.

So how do you interpret the conflicting information? When people see conflicting information, they usually abandon an intervention until there is more evidence. But this is one of the greatest mistakes they make.

1. Individualization: Scientific studies are based on a law of averages. And the chances are low that someone just like you entered the studies. So, even when they show efficacy, this means little about whether ti will work for you. Although we are far from having adequate data for individualization of health, start by making your individual diet diary now. Reflect on each of these anti-oxidants and food types, and ask yourself, 'Do I feel clear after eating cold blueberries?" or "Do I feel more intellectually stimulated after eating carrots or broccoli?" Then, reflect on data like this to support or refute your findings.

2. Work more intensively and intelligently with your primary care physician (PCP): Most PCPs will advise you generally. But if you want to get more specific information, ask your PCP the following questions:

- Given that you know my medical condition, which antioxidants do you think would be best for me?

- What doses do I need to take?

- Could a functional medicine doctor be helpful? Could you refer me to one?

- If I had to start a personal trial of adding one food, is this safe? Can we track my mental clarity and thinking over the next two-three months? This will help you individualize your personal trail once you know that the food is safe to take.

3. Look for combined benefits: Though the findings of antioxidants are conflicting, there are still some basic overall benefits that work. Most doctors will advise fresh fruits and vegetables, for example. This is still beneficial for your heart. So ask your PCP to work with you on "heart-healthy foods" that are also good for your brain.

4. Don't buy the massive generalizations on the Internet, scientific or otherwise: You might be tempted to follow the dietary advice of someone who does not know you, but avoids this. Whoever this is, is acting in a vacuum. They don't know your body and specific vulnerabilities. When you read something on the Internet (e.g. Why all antioxidants are good for you), check in with your doctor or nutritionist. They will help you balance out your view so that you can make informed decisions.

In general, I am a personal fan of antioxidants. But I don't use this randomly with my patients. If someone has a history of colon cancer or lung cancer, I will be more alert about β-carotene and Vitamin E. If they have restricted financial means, I won't recommend saffron, which is relatively expensive. If they have diarrhea or diabetes, I'll be cautious about the ketogenic diet. On every case, I will examine the person like themselves.

As helpful as scientific research is, the only true "evidence" base is the one that works for you.

About the Author
Uma Naidoo M.D.

Uma Naidoo, M.D., an Instructor in psychiatry at Harvard Medical School is the Director of Nutritional and Lifestyle Psychiatry at Massachusetts General Hospital.