In 2015, a new line of juices called Antioxia was released by Oasis. The carton boasts its antioxidant content on the front: “400 mg of polyphenols per serving.” If that wasn’t clear enough, larger letters above that claim also say “Health Break.”

Antioxia’s name may be a bit on the nose, but it’s just one of many products that promote their antioxidants to consumers. The most egregious example was POM Wonderful, the pomegranate juice that ran an advertising campaign a few years ago that touted the antioxidants in it as a fix for heart disease, prostate cancer and erectile dysfunction – even running ads with the tagline “cheat death.” It stopped only after a U.S. lawsuit successfully argued that the science didn’t support those claims.

Meanwhile, the media also promote the idea that antioxidants are a key to better health: A 2011 study found that the majority of the top three women’s magazines in Canada contained at least one article that mentioned antioxidants. Seventy-one percent of those described antioxidants as being good for readers’ health, and 36 percent framed the benefits as definite.

Yet the science doesn’t support that. Antioxidants have been researched for almost 20 years, with studies on hundreds of thousands of people. The results have been overwhelmingly lackluster, ranging from having no effect to significantly increasing the risk of death.

Given that evidence, is it time for us to give up on the idea that antioxidants are good for you? We dug into the research to find out.

What are antioxidants?

The theory around antioxidants starts with the idea that they fight free radicals. Those are unstable chemicals that are made when you eat, when you exercise, and when you’re exposed to pollution, cigarette smoke, alcohol, and the sun. These molecules grab electrons from other cells, a process that is thought to contribute to cancer, cardiovascular disease, diabetes, Alzheimer’s, Parkinson’s and eye diseases.

Antioxidants are the peacemakers in this scenario. Created naturally by your body or ingested through the food you eat, antioxidants contain extra electrons. Lab studies have shown that antioxidants like vitamins A, C and E give these extra electrons to free radicals, which neutralizes them.

Though all antioxidants have that in common, they come in thousands of forms, including vitamins C, E, and beta-carotene, minerals selenium and maganese, as well as polyphenols, flavanoids, and cartenoids.

While they all perform a similar function, they’re not interchangeable. Lutein, for example, exists in your eye, whereas beta-carotene does not. And some can amplify the effects of others: when vitamin E fixes a free radical, vitamin C will turn it back into an antioxidant so it can go to work on another.

Fruits and vegetables are high in antioxidants, and studies have shown that people who eat plenty of fruits and vegetables are less likely to get diseases like heart disease, vision loss and cancer. But many of those are cohort studies, where researchers look at how the habits of large groups of people relate to diseases. While they try to control for all relevant factors, it’s difficult to prove cause and effect this way.

“Cohort studies can be confounded by a lot of other lifestyle changes,” says David Jenkins, the creator of the GI diet and a scientist at the Li Ka Shing Knowledge Institute of St. Michael’s Hospital. Maybe people who eat more fruits and vegetables also get more informal exercise, or maybe they eat fewer carbohydrates. Or maybe something else in the fruits and vegetables – like fibre – is what’s really helpful.

Are antioxidants good for you?

That uncertainty is the reason why, in the 1990s, researchers moved on to the next step: randomized controlled trials that gave participants antioxidants in supplement form. That allowed the antioxidants to be compared against placebos, and to be tested in higher doses. Studies looked at a variety of antioxidants, from beta carotene and retinol to vitamins E and C.

It didn’t go well. In the mid-’90s, one of the first trials, the Beta-Carotene and Retinol Efficacy Trial, looked at the effects of supplements on 18,000 people who had been exposed to asbestos or who had a history of smoking. The study was stopped early after it became clear that the group taking the supplements had a 28 percent higher chance of getting lung cancer, and were 17 percent more likely to die. “If you protect the body’s cells, you may protect the bad as well as the good,” explains Jenkins.

Other large-scale studies found no effect. The Women’s Antioxidant Cardiovascular Study, published in 2007, looked at vitamin E, vitamin C, and beta-carotene in women who had a high risk of cardiovascular disease. It found the supplements had no effect on the likelihood of cardiovascular events. The Physician’s Health Study II, a 10-year-long project that looked at vitamin E and C in 14,641 men over 50, also found no effect on cardiovascular events.

Other research from the same study found that taking those supplements didn’t lower the risk of cancer either. The 12-year-long Selenium and Vitamin E Cancer Prevention Trial (SELECT), looked at the effects of various antioxidants on 35,533 men – and found no effect on prostate cancer. A 2013 systematic review concluded that antioxidants don’t lower the risk of cancers or of cardiovascular disease.

There have been a few positive results, most notably from the Physicians’ Health Follow-up Study, which looked at people taking beta-carotene for 18 years – longer than the other trials – and found that people taking the supplements had slightly better cognitive skills.

For the bottom line, we can look to a 2012 Cochrane review on antioxidants. It covered 78 randomized clinical trials on antioxidants. Together, those trials included more than 200,000 healthy people and more than 80,000 people with stable diseases, such as cardiovascular disease.

On the whole, the review found a slightly negative effect. People who had taken antioxidants were three percent more likely to die – a trend that showed up more strongly in trials with a low risk of bias. That risk was true for beta-carotene, possibly true for vitamin E and vitamin A, and wasn’t seen in vitamin C or selenium.

The bottom line

Now we know that antioxidants – when taken as a supplement – aren’t good for you. So how does that fit with the research that shows fruits and vegetables are good at preventing disease?

There are many theories. The lower doses of antioxidants in fruits and vegetables might make a difference. Antioxidants could be combined in a different way in whole foods. Or something else in those foods could be what’s beneficial – or could be making the antioxidants effective.

Or these studies might be missing the segment of the population that they help by focusing on too broad of a group. “People are so heterogeneous, therefore in big trial, our effect may be buried inside the variation in people,” says Oliver Chen, interim director of the antioxidants research lab at Tuft’s university.

Jenkins, for one, is optimistic that antioxidants are an important part of fruits and vegetables. Studies could return poor results because researching nutrition is very difficult, he explains. “The field is very messy,” he says. “We’re asking big questions: What’s the length of time to generate a disease, whether the food form is the same as the supplement, whether the diet itself may interact with the supplement… You’ve got a lot of questions there.”

Others, like Yoni Freedhoff, the medical director of the Bariatric Medical Institute in Ottawa, are less convinced. “People appreciated the fact that there seemed to be health benefits from diets rich in fruits and vegetables, and then they proposed – from principles that made sense on paper – that it was the antioxidants that were the component that was leading to benefits,” he says. “But just because something sounds like it could plausibly true doesn’t mean that it is. The research to date – if you’re generous, you might suggest that it’s underwhelming.”

Antioxidants may turn out to be acting differently in foods to offer a health effect, he says – maybe there are synergistic effects, for example. But right now, that’s all very much unproven.

Based on the studies that we do have, the takeaway for the public is simple: don’t take antioxidant supplements, especially since the research suggests they may be harmful. And don’t be swayed by processed foods that tout antioxidant benefits. “The fact that we still allow companies in Canada to promote their products with claims of antioxidants to me is unfair to the consumer, who certainly is not aware or caught up with the medical literature,” says Freedhoff.

But do eat plenty of fruits and vegetables, because something in them really does seem to fight disease. A 2014 systematic review published in the British Medical Journal found that every additional serving of fruits and vegetables reduces your risk of death by five percent, up to five servings a day.

That much, at least, we know.