Getty Images

A new report shows antioxidants do not boost fertility as previously thought. It’s not the first study to take the shine off the popular agents, which many people take in supplement form.

In a review published in the Cochrane Library, researchers found that antioxidants did not increase women’s chances of conceiving or having a baby, which wasn’t surprising, given that the quality of trials linking fertility and antioxidant supplements, say the scientists, was low. But the findings did contradict earlier studies that found partners of men who took antioxidant supplements were more likely to conceive than those who took placebo. And the review is only the latest to raise doubts about the health benefits of antioxidants, which have been touted as potent cancer-fighters and anti-aging allies. Once present only in foods such as berries, carrots, peppers and tomatoes, antioxidants are now added to flavored water and other products to earn a “high in antioxidants” label. But are the benefits of antioxidants overhyped?

(MORE: The Supernut: Walnuts Pack a Powerful Dose of Antioxidants)

Antioxidants entered the public’s nutritional vocabulary in the 1990s, when researchers began to understand how free radical damage, caused by oxygen-based reactions, contributed to chronic diseases from aging to vision loss and cancer. Free radicals are generated as cells use oxygen to break down food for energy, and they can cause cell damage by attaching to other molecules and prompting cells to grow abnormally or by interfering with normal cell functions, including those in the brain. Free radicals are a natural byproduct of the body’s metabolism, but in most cases, naturally occurring antioxidants stabilize them and keep the damage to a minimum.

When that balance is disturbed, however — and anything from exposure to pollutants to cigarette smoke to things you eat can shift this equilibrium — the production of free radicals may outrun the body’s ability to control them. That’s why antioxidants became a popular weapon in the fight for well-being — if the body needs more antioxidants, it couldn’t hurt to supply them in supplement form, right?

(MORE: Popcorn Is Packed With Antioxidants)

The problem is, antioxidants come in a range of forms — from vitamins like vitamin C, vitamin E, and beta-carotene, as well as minerals like manganese and selenium. Then there are the other carotenoids and flavonoids and polyphenols. And, not surprisingly, each can have a different effect on the cells of the body. In recent years, for example, scientists reported that beta-carotene, instead of lowering cancer rates, actually increased risk of dying from lung cancer or heart disease among a group of smokers. In a recent article published in the journal Trends in Pharmacological Sciences, toxicology researchers from Maastricht University in the Netherlands highlighted the all-or-nothing beliefs about antioxidants, noting that it’s likely that the agents have some health benefits, if used and dispensed in the proper doses. They write:

For several decades, we have noticed that the antioxidant pendulum appears to swing vigorously from ‘only healthy’ to ‘extremely toxic’, and from ‘natural antioxidants are best’ to ‘antioxidants cannot act’. The squabbling parties do not seem to listen to counter-arguments. Erroneous statements are not corrected, and thus the pendulum oscillates to the extremes. This inevitably hampers research in the field and confuses both scientists and consumers. As a consequence, we might fail to spot opportunities for which antioxidants may aid in optimizing health.

So what does the research say about what antioxidants can, and cannot do to improve your health?

All antioxidants are not equal: Because antioxidants come in many different types, it makes sense that you consume a variety of antioxidant-rich fruits of vegetables, so that you can benefit from the full range of benefits they provide. Together, the mix is good for your health. For instance, certain antioxidants may play a greater role in preventing certain diseases, such as cancers, while others are better at combating neurodegenerative conditions.

In a study of Dutch people published in the journal Neurology in February, researchers were disappointed to find no correlation between antioxidant-rich diets and cognitive decline or stroke, but, as Elizabeth Devore, an instructor in medicine at Harvard Medical School in Boston and one of the study authors, told HealthDay, “There are thousands of antioxidants in the diet, and some of them may have more antioxidant power.”

Most people don’t get enough antioxidants from naturally occurring sources: For most healthy adults, the antioxidants contained in a healthy diet rich in fruits and vegetables would be enough to combat most of the free radical damage occurring in their bodies. But, says Jeffrey Blumberg, director of the antioxidants research laboratory and professor of nutrition at Tufts University, most people fall far short of meeting recommended daily intakes for vitamins like C and E. The average adult should be consuming 15 mg of vitamin E daily, but more than 90% of people fail to eat that amount, and most people only get about half the recommended dose from their diet. “That’s a huge shortfall. That doesn’t mean they couldn’t, but they aren’t. Vitamin C is another shortfall nutrient, or a nutrient of concern. Vitamin C and E are low in the typical American diet. With vitamin C, women require 75 mg a day and men 90 mg per day; that’s really low. Have a glass of orange juice and you have practically met your entire requirement for the day. It is so easy to meet your vitamin C requirements. It’s shocking to me that people aren’t,” says Blumberg.

But more isn’t necessarily better — it’s about getting just the right amount to balance the free radical activity in the body. And that’s why nutritionists don’t recommend loading up on supplements to make up for what you can’t eat daily; it’s not clear how safe getting too much of certain antioxidants are (some, like beta carotene, can increase risk of premature death), and it’s easy to overdo a nutrient if you’re taking supplements.

Be skeptical of claims that antioxidants extend your life (or that they can kill you): “Are the claims surrounding antioxidants a bit overblown? Well yes, if it says antioxidants will prevent Alzheimer’s disease, cancer, heart disease, eye diseases, kidney disease and everything, then yes, it is a little overblown,” says Blumberg. “Any clearly definitive, absolute claim is overblown.”

There are legitimate claims, however, that you should discuss with your doctor. For example, there is evidence that vitamins E and C may help reduce the risk of age-related macular degeneration, the leading cause of blindness in older adults, and protect against age-related eye damage.

There is no “superfruit”: There is no evidence that antioxidants can keep most chronic diseases at bay, but the food and beverage industry continues to make claims that super fruits like pomegranate or pitaya can minimize oxidative damage. But “superfruit” is a marketing term that is not recognized by the Food and Drug Administration (FDA) or the US Department of Agriculture (USDA) as conveying any scientifically supported nutritional benefits.

And what about processed snacks and beverages that boast high levels of antioxidants? “The challenge here is that since consumers understand that by and large antioxidants are good for you, they are going to use that as a hook to sell you their products,” says Blumberg. “If they are formulated into a product that you don’t necessarily think of as particularly healthy, like soda pop, then be skeptical. I would argue even if they provided 100% of the daily value of vitamin C inside a sugar-sweetened beverage, it’s probably not the best source to get it from.”

(MORE: In Search of…The Superfruit)

Everything in moderation: We can all benefit from some antioxidants — but these should come from the diet, where it’s likely to be in the right variety and the right amounts. And it’s more important to get certain ones, such as vitamins C and E, than some of the thousands of phytochemicals and carotenoids that present in various foods. “The central ones, vitamin C, vitamin E, zinc–are essential. If you don’t get them, in extreme [cases], you can develop a deficiency problem. But there are lots of other basic research and human studies that suggest if you get an adequate amount, you promote health and may reduce your risk for some age-related chronic diseases,” says Blumberg. As with most things involving our health, getting the dose just right is the key.