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The downside to antioxidants

One-half to two-thirds of American adults use dietary supplements as part of an overall effort to follow a healthier lifestyle. The use of supplements is higher among women (than men) and usage increases with age. People who exercise are also more likely to use supplements.

Since the 1990s, the food and supplement industry has touted the health benefits of antioxidants and, today, antioxidant supplements represent a $500 million industry that continues to grow. Added to breakfast cereals, energy bars, energy drinks, vitamin water and other processed foods, antioxidants have been promoted as additives that can help prevent heart disease, cancer and memory loss, among other conditions.

The “dark side”? High doses of single-nutrient antioxidant supplements — such as vitamin E, vitamin C, selenium and beta-carotene — can potentially accelerate the aging process and increase cancer risk, rather than having a protective effect.

We talk to fitness and nutrition expert Shawn Talbott, Ph.D., L.D.N. and author of the forthcoming book, Deadly Antioxidants, who shares his expert insights with us. “Antioxidants are essential nutrients that our bodies need and they are protective — but only up to a certain point. Overconsuming antioxidants can actually cause more damage in the cell,” he says.

Oxidation, free radicals and the role of antioxidants

To understand how antioxidants benefit us, it is also important to understand what oxidation is and how free radicals are created.

Oxidation is a natural process that occurs when oxygen interacts with cells of any kind. For example, you can see the result of oxidation when apple slices (exposed to oxygen) turn brown, or when a cut finger becomes inflamed. Atoms that have been exposed to oxygen will “break” and end up with unpaired electrons, creating unstable molecules, called free radicals.

“We have a baseline exposure to free radicals just by being alive, breathing oxygen and metabolizing our food,” says Talbott, who adds, “From the oxygen that is used to convert our food into energy, two to three percent of that oxygen converts into free radicals — it just comes with the territory.”

Having too many free radicals in our body, however, can damage DNA and cell membranes, resulting in tissue damage that leads to chronic diseases and conditions that become more common as we age, including arthritis, vision loss, heart disease, cancer and dementia.

Sources that generate problematic free radicals include:

  • Cigarette smoke
  • Air pollution
  • Car exhaust
  • Excessive exposure to sunlight
  • Overtraining
  • Poor diet
  • Pesticides and toxins in food and water
  • Excessive consumption of alcohol

Antioxidants are protective molecules that can prevent or slow cell damage. As the “good guys,” antioxidants can inactivate a free radical, so that it cannot cause cellular damage. Natural antioxidants are found in fruits and vegetables, and the most common dietary antioxidants are vitamins A, C, E, beta-carotene and lycopene. Synthetic forms of antioxidants can be found in supplements.

“Oxidative balance is the proper balance between free radicals, or ‘damaging’ molecules, and antioxidants, which are ‘protective’ molecules,” says Talbott.

With antioxidants, more is NOT better

Those of us who are health conscious tend to think that if a few antioxidants are good for us, then more must be better. Unfortunately, research now suggests that taking high doses of isolated nutrients can cause more problems than they prevent.

For example, a large trial of beta-carotene was conducted among 29,133 Finnish men, all smokers, at high risk for developing lung cancer. Smokers who took the beta-carotene supplement had significantly higher rates of lung cancer than those who took the placebo. A 2011 study published in the Journal of the American Medical Association tied vitamin E supplements to an increased risk of prostate cancer. And another study published in the Journal of Nutrition reported that supplementing with vitamin C, vitamin E, beta-carotene, selenium and zinc increased the risk of skin cancers in women.

Eat a rainbow of fruits and vegetables

When it comes to antioxidants, Talbott advises consuming small amounts of a wide variety of antioxidants for a beneficial, synergistic effect — rather than taking high doses of any single antioxidant, which can have a potentially harmful effect. “Your best approach is to eat 10-12 servings of different, brightly colored fruits and vegetables throughout the day. Organic and local foods will also be higher in phytonutrients than conventional produce,” he says.

When you consume even low levels of antioxidants (e.g., through whole foods) your body is able to naturally increase its own production of antioxidant enzymes within cells that can be up to one million times more effective in fighting free radicals. In other words, “making” your own antioxidants (internally) may be much safer and more effective than “taking” (externally) high doses of antioxidant supplements.

Activating your body’s own “security system”

How can we encourage our body to protect itself and turn on its own internal antioxidant defense systems?

One simple way is by eating foods that activate Nrf2 — a powerful protein within each cell in the body, which stimulates production of our body’s most important antioxidants.

“Nrf2 is at the very center of this cellular protective pathway, and it serves as a ‘master regulator’ of the body’s antioxidant response. Think of Nrf2 as a ‘thermostat’ within our cells that senses our level of oxidative stress and other stressors, and turns on internal protective mechanisms,” says Talbott.

Some of the best Nrf2 activators are plants that may not necessarily be antioxidant rich, yet trigger vigorous antioxidant production — like sulforaphane, an organosulfur compound from cruciferous vegetables.

According to Talbott, some of the best foods, spices and herbs for “turning on” Nrf2, so that cells can produce their own antioxidant enzymes, include:


  • Broccoli
  • Brussels sprouts
  • Cabbage
  • Cauliflower
  • Blueberries


  • Turmeric
  • Cinnamon
  • Ginger
  • Rosemary
  • Thyme
  • Sage


  • Milk thistle
  • Green tea
  • Bacopa
  • Ashwagandha

With age, we acquire a higher level of oxidative damage.

To help reduce age-related increases in oxidation, Talbott recommends regular consumption of spices as an “intervention.” Just sprinkling spices on food (such as those listed above) is enough to deliver a small degree of Nrf2-inducing benefits. For spices taken in supplement form, Talbott advises taking around 100 mg, a safe and effective level for Nrf2 effects. “That’s not very much — about 1/50 of a teaspoon. However, it is these very small ‘doses’ of spices, used on a regular basis, that are associated with the best long-term health benefits — not isolated, mega-doses of antioxidant supplements that may cause potential harm,” he says.

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