Is it true that antioxidants can actually cause cancer?

Image Credit: Anders Sandberg / Flickr

Is it true that antioxidants can actually cause cancer?

Hi Dr. Greger, appreciate all your work. There’s been a lot of bad news a about antioxidants recently. Should people be concerned about how much they ingest? 

Ren / Originally posted in Acai to Zucchini: antioxidant food rankings


Good question! There has been a buzz around the internet from headlines like this: Study: Antioxidant use may promote spread of cancer. Whenever I see a title like this I take a step back to see what’s really going on. The most healthful and nutrient-rich foods in the world come from plants, which overwhelmingly have the most antioxidants.  How could it be possible that cancer risk increases when eating antioxidants? It seems like the exact opposite of what professionals have been saying for decades! Let’s explore the article and see if we can make some sense of it.

It appears the study basically took mice and injected them with high doses of an antioxidant drug (N-acetyl-cysteine). This may help guide veterinary oncologists for your pet mouse, but when it comes to making decisions for the rest of your family I’d suggest relying on human trials where people eat actual food. Dr. Greger says in his post on lung cancer that “antioxidant supplements are not an effective replacement for eating real veggies. Lutein pills have even actually been shown to increase the risk of lung cancer.” And furthermore we’ve known for years that supplements like folic acid may increase cancer risk, but eating beans and greens are super healthful. 

When headlines like this appear I look to NutritionFacts and read the science. I just looked up Dr. G’s summary on vegetables and with over 75 articles and videos on veggies I don’t see any reason to avoid naturally occurring antioxidants from whole foods. Instead of popping harmful supplements that are a waste of money, I’m slamming down some spinach greens with roasted sweet potatoes and red beans for lunch. All of which are full of antioxidants and have been shown to decrease the risk of several cancers. (What about soybeans? Watch videos on soybeans and breast cancer and should I stay away from soy if I have breast cancer?).

Plants may help protect us from diabetes, depression, stroke and heart disease, and even certain cancers. Find out what some of the best cancer-fighting vegetables to eat might be? My favorite biochemistry professor, Dr. Kent Littleton from Bastry University, always said, “Joseph, remember that the body is a better biochemist than any of us!” That quote really stuck with me. The body just knows how to package antioxidants when we eat them as nature intended. It’s all about the whole plant-foods!

For more related videos check out: How to Reach Antioxidant Recommendations. Dr. Greger covers the minimum amount of antioxidants to shoot for daily. Also, see Dr. Greger’s Optimal Nutrition Recommendations

Image Credit: Anders Sandberg / Flickr 


19 responses to “Is it true that antioxidants can actually cause cancer?

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  1. Hi Joseph and Dr. Greger,

    I do my best to consume a minimally-processed plant-based diet, and the only vitamins I take are D and B12 (as per Dr. Greger’s recommendations). But I have Mast Cell Activation Syndrome, a disorder in which my mast cells are overly excitable and degranulate to a multitude of triggers, releasing histamine and causing almost chronic inflammation and almost daily anaphylaxis. To avoid dependence on many medications with side effects, I have been taking a quercetin supplement for the past year, which has greatly reduced my inflammation and stopped the daily anaphylaxis (which I now experience only every week or two). I thought this was a miracle. I try to eat quercetin-rich foods, but the amount I can get from diet doesn’t seem to be enough to make a significant difference.

    However, another MCAS friend just shared this study linking. quercetin supplements with cancer. I don’t understand most of the scientific lingo, so I was hoping you could help interpret it. It seems to be saying the same as this article, that antioxidant supplements are bad news? My other option seems to be medications with unpleasant side effects and long-term damage. However, if I really focused and was able to eat the effective amount of quercetin from food, would it still have the increased cancer risk? Any advice?

    Thank you for any help you can give!

    1. Hello Mary Z, I am a family physician and volunteer moderator for this website. I just looked at the article you referenced. Almost the entire article was about luteolin, not about quercetin; the authors say “Quercetin exhibited weaker estrogen agonist activity and progestin antagonist activity than luteolin”. When I looked up “quercetin deleterious effects” on PubMed (free database of medical articles), most of the articles cited are actually about beneficial effects of quercetin.
      Given that you are having real benefits from your quercetin supplement, and no side effects, and that other treatment options have side effects for you, I don’t think you need to worry about this.

  2. Mr. Gonzales, you stated, “I’d suggest relying on human trials where people eat actual food.” Do you have links to any such research studies? I’ve looked on PubMed (albeit fairly briefly) and haven’t found any. The fact that all links in this article point to other articles on this web site isn’t quite the same as research-supported statements. Hoping you can help, thanks.

  3. When I was on chemo and radiation, I was instructed to avoid antioxidants, especially the pill forms. But, of course, by then it was too late. Hopefully, my new diet will prevent a recurrence.


  4. Hi,
    I am a vegan of course. However, I have not seen a discussion on pure water. If your whole food is full of chemicals, organic or not- just because of depleted soil – what about water. I just listened to a group Water Liberty – and they (Japan – has developed a liquid mineral supplement that kills all the bad stuff in your water so you can drink fresh water even if it is has already been filtered. You can also use this water to clean all of your vegies and fruits. It is called Black Mica extract. Suplfur minerals. It neutralizes the horrible chemicals in our water. It was developed by a Dr. Asao Shimanishi in Japan. I did order some because – our water is full of cataminents. To tell you the truth you have to have excellent water at this point to drink, cook, and clean your food. Thanks. Ra

  5. Hi Dr. Gregor,

    I recently learned about Fulvic acid minerals. I cannot find anything on your site about it. It’s in the form of black water and supposably has a high concentration of antioxidants. Also some alkalinity and all natural due to it coming directly from the earth. It sounds good on the surface from what I have read and viewed on YouTube but I am no expert. I trust your expertise and wonder what your thoughts would be on it.

  6. I read what seem to be legitimate research articles connecting paraoxonase to healthy HDL, paraoxnase to pomegranate consumption, and efflux of ox-LDL from blockage site macrophages dependent on paraoxonase strengthened HDL. Since I had mammoth blockages (99, 99, 80 on mains, over a dozen downstream blockages and aneurysms) and recent emergency bypass surgery, and expected to die in three years from heart failure, I started drinking pomegranate juice. Daily now for almost 10 years, and other high antioxidant fruits, plus a very low fat diet. I am doing well, and very athletic.

    Anthocyannins in red and blue fruits, antioxidants in herbs and spices, etc to help myself. I have my angiograms on stick memory, and a google share drive. The videos scare medical people.

  7. I just watched your cinnamon video, and I’m wondering if there is a safe amount of cassia cinnamon to consume, if so what is that amount and do you recommend it?

    1. Thanks for your question Michelle.

      Are you referring to this video?

      If so, then yes, there is potential harmful effects of cassia cinnamon on the liver and therefore It initially had a TDI (Tolerable Daily Intake) of 2mg/kg bodyweight max, but was lowered to 0.5 and currently stands at 0.1mg/kg bodyweight (see here).

      So for a 60kg individual, this translates to 6mg of coumarin per day. According to this review, “Cassia cinnamon contains up to 1% coumarin”.

      Hope this answer helps.

  8. Hi Doctor Greger and Josesp. I wasn’t sure where I could post this but I had some questions about intermediate fasting. Lately, intermediate fasting has become more popular and I’ve been seeing articles about
    it poping up about it. Is skipping meals like breakfast healthy? Or what about fasting once a week or every two weeks for a healthy individual of normal weight? I’ve read some articles that claim it lowers cholesterol and helps clear up your arterial plaque. Is there any truth to these claims?

    1. nekomime: Lots of people have asked about the topic of intermittent fasting. I believe that Dr. Greger is planning on addressing the topic in a future video. Stay tuned!

    2. Time restricted eating, especially earlier in the day (for example, eating between 7am-5pm),is associated with lower breast cancer risk and recurrence rates. ( I know it’s a youtube link and seems uncredible, but it’s a great podcast interviewing Ruth Patterson, Ph.D. She’s a professor at UC San Diego. The whole podcast is about time restricted eating and it’s benefits, it’s worth looking at.

  9. hey docs; great work. I’m an old Vietnam vet geezer living in my truck without a refrigerator and I’m on a very limited daily food budget as I try to get my daily dozen in. Two questions: 1) May I substitute berry powder such as amla for the edible berry serving and, if so, how much? 2) I have hypertension and need my nitrates from leafies but have confused myself on the issue of whether to eat them with fat or not. Can you “unconfuse” me? thanks in advance.

    1. Hello Buddhadawg,
      Thanks for your question. I’m a family doctor in private practice and a volunteer moderator for this website. The general answer to your question is that you would be better off eating the actual berries. Dr. Greger has done numerous videos in which he cautions about using too many supplements, and instead recommends eating whole plant foods, which are cheaper, and usually much better for you. Here are a few of those videos:
      This one shows that many supplements don’t even contain what they say they do
      Here is one that looks at supplements vs. whole plants in treating asthma.
      – Here is a short video showing that supplements can even be dangerous.

      Regarding nitrates: good for you, for eating green leafy vegetables to help control your hypertension.
      You might have seen this 2012 video by Dr. Greger about nitrates and HTN. The answer is that NO, you should not eat them with fat, especially if you mean animal fat, which contains carcinogenic nitrosamines, as Dr. Greger mentions in this video. If you are asking about whether or not to add vegetable oil (e.g. olive oil) to your salad, even olive oil is 100% fat, and could raise your cholesterol. However, unless you are obese, eating a small amount of healthy plant oils (flax-seed, canola, olive, etc.) is not going to hurt you.
      I hope this helps.

  10. Hi,

    I am not sure whether this is the right place to post this question but I am going to anyway. I have watched almost all videos of Dr Grregor on the channel and I love each and everyone of them. I even watch one of this talks about how most of the leading causes of death can be reversed and prevented using a plan based diet.

    Me and my wife have been struggling with infertility for almost 3 years now. Doctors say that we have unexplained infertility however they do point out that my wife has low AMH level. We even underwent a failed cycle of IVF. My question to Dr Gregor is whether there a plant based diet for me and my wife help? Or are there any foods that help in increasing AMH levels in women?


  11. Thank you for your question. Sorry to hear about your troubles. A whole food plant based diet is certainly the best for preserving fertility. For male fertility, other pollutants are important and discussed in these articles.

    Sadly though, above and beyond a plant based diet, I don’t think there are any other specific foods that can help your wife. If her hormones levels are menopausal or peri menopausal I don’t believe that this can be reversed through dietary measures.

    1. Hi, Joe! While antioxidants in whole plant foods have been shown to provide a variety of benefits in the body, antioxidant supplements do not have the same benefits and in many cases can actually do more harm than good (for example, see here:, here:, and here: The antioxidant activities of plant foods are thought to derive from their additive or synergistic effects—meaning the whole may be greater than the sum of its parts. This helps explain why a pill simply cannot replace the complex interaction of phytochemicals present in whole plant foods. (

      As stated in the post above, “Dr. Greger says in his post on lung cancer ( that ‘antioxidant supplements are not an effective replacement for eating real veggies. Lutein pills ( have even actually been shown to increase the risk of lung cancer.’ And furthermore we’ve known for years that supplements like folic acid ( may increase cancer risk, but eating beans and greens are super healthful.”

      It is much more worthwhile to obtain antioxidant abundance by enjoying a diet rich in whole plant foods!

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