Huge claims are made for antioxidant supplements. Is any of this proven?

It seems antioxidant supplements are currently being touted by numerous sources as being extremely vital and necessary components of nutrition and good health. It’s almost an article of faith that antioxidants will reduce the risk of heart disease, cancer etc. However, when I look for specific evidence of the scientifically proven efficacy of antioxidants the answers don’t appear to be as clear. Despite studies being performed there doesn’t appear to be a clear consensus on how effective they are.

Are the health claims being made for antioxidant supplements plausible?
From How Stuff Works - How Antioxidants Work

Do Antioxidants Improve Health?

From Wikipedia

In some cases a possible negative effect is postulated

And finally, the American Heart Association says

IMHO, there are sound biochemical reasons for taking small amounts of supplementary antioxidants, small being the operative term here. More is superfluous and is very likely detrimental. The people who tout antioxidant supplements seem to always neglect the fact that higher mammals already have a sophisticated set of hepatic enzymes for dealing with reactive oxygen species. Antioxidants work bloody wonders in Drosophila melanogaster—extending their natural life span by upwards of two or three hundred percent. But when you start getting to the level of biological complexity of even a field mouse, results diminish dramatically. My armchair biochemist guess goes something along these lines: if you took two identical twins and one took antioxidants and the other didn’t, the one who did would fare slightly better in old age. He might live a few months longer than his unsupplemented twin, and some of the biomarkers of old age such as arthritis will be less advanced. But both twins will look more or less the same at an advanced age.

In the book “Bad Science”, Ben Goldacre says there is no scientific proof of the benefits of taking antioxidants, and in some studies they have even been found to be harmful. Yet, antioxidants are added or advertised in almost everything we eat today, like people know it’s good for them.

Is this all a HUGE marketing campaign, or has there been proof of the benefits of taking additional antioxidants? Wikipedia right now doesn’t seem to show any benefits.

I will state without cites that although the epidemiological evidence suggests a benefit for antioxidants (i.e. strong inverse correlations in populations between antioxidant use and things like heart disease), prospective, randomized, controlled trials have NOT shown any such benefit. In fact, some of them even demonstrated net harm in those randomized to antioxidant treatment, e.g. vitamin A and lung cancer.

As an aside, a similar pattern (i.e. epidemiological protection but randomized trial net harm) was found for postmenopausal estrogen supplementation.

The trouble with all this is the use of surrogate endpoints. Many medical things are promoted because they do things that seem correlated with good health, but that doesn’t prove that medicalizing it improves health.

As an example, high blood pressure shortens life. That much has been well demonstrated. Less clear, but true, salt raises blood pressure (in some people). Conclude that a low salt diet makes you live longer. Well, the evidence isn’t all in, but it seems that people who ingest about 5 g a day live longer. Some ultra-low-sodium diets have you using 1 g a day. But that appears to shorten life, although the evidence is not entirely convincing.

High cholesterol, especially the low-density form, shortens life. So statins, which lower cholesterol levels should lengthen life. And the evidence is that they do, on average (but they can also, in some people, cause liver problems and must be watched). But there is at least some evidence that the cholesterol lowering effect may not be the reason. They also suppress inflammation and that may be their mode of lengthening life. Maybe directly targeting inflammation would do better.

There seems to be no evidence (and some in the other direction) that anti-oxidants lengthen or improve life.

Karl and Hari,

Would you both agree that the evidence supporting a diet high in antioxidant-rich foods has good evidence of beneficial health effects?

That epidemiological evidence is pretty strong in some cases. Thing is that the leap from even assuming that the beneficial effect of diets high in these foods is due to antioxidants in some way to the conclusion that supplementing a few antioxidants in isolation of those food matrices will be of benefit, is quite a large one that has little to support it.

Using “high antioxidant” as a marker of foods to include in your diet (like citrus, apples, berries, nuts, various vegetables, dark chocolate, turmeric, and so on) seems fairly well supported; adding supplements instead of foods, not.

That’s going to be hard to pin down… I see news reports, particularly about diabetes or diabetes-caused ailments, that offer up the breathtaking news that eating a balanced diet with a mix of fruits & vegetables (which is going to include a bunch of anti-oxidants) and un-processed foods is healthier for you.

I have a background in model organism aging research*, so I have a bit of knowledge on the topic. Accumulated oxidative damage is one of they hypothesized causes of aging. The damage certainly occurs, and it certainly isn’t helpful. So, the thinking goes, if we give you antioxidants, they will prevent oxidative damage and perhaps slow the damage that leads to aging.

One problem is that “antioxidant” is a broad and (IMO) not very useful descriptor. There are antioxidants that are made by your body, and are essential for all sorts of biochemistry. There are antioxidants that happen to be essential nutrients. There are yet other antioxidants that are found in food, and may have beneficial properties that are unrelated to their antioxidant properties. And there are antioxidants that are harmful, though we usually don’t refer to them as such.

Your body also makes antioxidant enzymes. I’m aware of a number of studies that have genetically engineered various model organisms to increase the production of these enzymes. Off the top of my head, in these experiments huge amounts of antioxidant enzymes have little (if any) effect on life span or health. Some dietary antioxidants do increase life span or health of various critters, but there’s often conflicting evidence. IMO, when there is an effect, it is due to drug-like properties of that particular molecule, rather than antioxidant properties.

Now, there is very strong epidemiological evidence that diets high in antioxidants are correlated with health and longevity. My semi-WAG is that this is not simply due to antioxidant properties. There may be some antioxidants that happen to have (unrelated) benefits. I think, however, that much of the correlation is due to underlying causes. Really, diets high in antioxidants are high in fruits and vegetables, and low in big macs and pancake-wrapped-sausages and corn syrup. And there are probably all sorts of other confounding factors – life style, activity, income, etc.

Basically, I think oxidative damage is just one of many things that contribute to disease and aging, and simple antioxidants won’t do much to reduce oxidative damage.

  • mostly related to worms and flies and the like, though I’m also somewhat familiar with work done with rodents. Though we really don’t know how much of this research is relevant to humans…

The rule of thumb (for me, at least) is not to take mega-doses of anything, particularly whatever is being hyped at the moment. Vitamin C, vitamin E, glucosamine, chondritin, etc. have been shown to have either zero effect on the condition they’re supposed to treat, or worse, can cause harm in the dosages people take them in. The people that make these things are always on the lookout for the latest hype-able item (acai berries, anyone?). There are some things that seem to help with some conditions, such as saw palmetto for prostate health, but by and large this stuff is just made to line the pockets of charlatans.


Well one was provided in my post, Surreal, and while there are many, do you really require a set of comprehensive citations demonstrating that a diet high in those high antioxidant foods (citrus, apples, berries, many other fruits, many vegetables, nuts, dark chocolate, turmeric, etc.) is correlated with health and longevity? Really?

Here then. Get the whole article and check out the citations of that review which concurs with what has been said here:

Here are a few more, which specifically look at the connections between high-antioxidant diets and cardiovascular health, cancer, and overall longevity.

Antioxidant vitamins in the prevention of cardiovascular disease: a systematic review

Fruit, vegetables, and cancer prevention: A review of the epidemiological evidence

Traditional Mediterranean diet and longevity in the elderly: a review

Anyone else read the thread title as “Huge clams …” ?

Those foods are basically good healthy foods clearly. Well, chocolate maybe not and I don’t know how you can ingest enough turmeric to matter. But who knows what part of the foods is relevant. Maybe the lack of animal fat, of simple sugars. And how would you test it? But you can test, say, vitamin C supplements, and they don’t seem to show any effect and maybe even a negative effect. Eating healthy foods certainly contributes to health (actually that is a tautology, since that’s what we mean by healthy foods).

Yes, really.

I’ve heard so many opinions expressed about health matters with absolute certainty, yet upon investigating the actual science I found the evidence to be lacking, ambiguous, or in some cases completely contradicting the mainstream opinion (a calorie is a calorie, dietary cholesterol raises blood cholesterol and causes heart disease, saturated fat causes cardiovascular disease, skipping a meal will put you into “starvation mode” and ruin your metabolism, drinking raw milk is very risky, water fluoridation is a risk-free boon for public health, homebirthing is more dangerous than hospital birthing, melanoma is caused by excess sunlight, dietary sodium should be limited even for those who are not salt sensitive, etc.). I don’t think we should assume anything.

So the facts now are:
[li]People with diets high in antioxidants are healthier/live longer[/li][li]Artificially supplementing antioxidants doesn’t seem to help[/li][/ul]

Where does that leave uncommon foods high in antioxidants like acai? If a new food was discovered to be high in antioxidants, is it likely to be good for health?

I for one am not sure. The track record is that “high in antioxidants” is a good correlate of a complete food having healthful benefits (or minimally that people whose diet include lots of them have better health outcomes … it could just be a marker for some unidentified confounder), but that does not necessarily mean that higher is better, or that all foods high in antioxidants are healthy. Based on the track record I’d think “likely” seems like a fair assessment but how likely? I don’t think any one can really say and some could with just cause debate if “likely” is even warranted.

That said I like the taste of acai juice, pomegranate juice, and carrot juice. So including them in my diet is a no-brainer. Why not?