They've been touted as a tonic for almost anything that might ail you – from the common cold to cancer. But despite the marketing hype, evidence continues to mount that antioxidant supplements are no panacea. Far from being a cure-all, they could even do you harm.
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An updated Cochrane Review of 5 antioxidant supplements – beta-carotene, vitamin A, vitamin C, vitamin E and selenium – is the latest in a series of studies to raise a red flag.
The Cochrane Collaboration is an international organisation that systematically reviews health-care interventions. Its review found no evidence to support supplement use in the general population or in patients with various diseases that were in a stable condition.
After assessing 78 randomised trials involving more than 250,000 participants, the authors concluded there was also an increased risk of mortality associated with supplements containing beta-carotene and possibly with those containing vitamin A and vitamin E.
Hype about antioxidants has spawned an avalanche of health claims.
The current fad has its roots in a series of studies that showed a link between diets rich in fruit and vegetables and a lower risk of chronic diseases such as cancer. Antioxidants and their potential to fight free-radicals gained attention as the substance in fresh produce that might be responsible for its health-giving properties.
It wasn't long before antioxidant supplements started appearing on the market accompanied by a raft of therapeutic claims. The supplements have also been added to packaged foods such as breakfast cereals in an effort to boost their nutritional appeal.
But the health hype has had little backing from large-scale scientific trials. The Cochrane Review – well regarded in medical research circles – concluded that the vast majority of nutritional-intervention trials have shown no obvious benefits from antioxidant supplementation in otherwise healthy people.
Professor Margreet Vissers from Otago University's Centre for Free Radical Research believes the reason most supplement trials have shown no benefit is because supplements don't affect the body's antioxidant status. Most people taking a supplement don't need to, she says, and there's no evidence that taking more is better. She believes consumers are being sold false promises.
"There is really good evidence that a diet high in fruit and vegetables is associated with better health outcomes. Beyond that, the jury remains out."
Professor Vissers says scientists are still getting to grips with how the compounds in food work in the body. Isolating food elements and taking them as supplements won't necessarily have the same effect as eating the food and may even have unexpected effects, she says.
Dr Carolyn Lister, a scientist at Plant and Food Research and author of a 2003 book on antioxidants, agrees: "There's still a lot to learn about the myriad of compounds in foods and how they benefit health." Foods are far more complex than the "silver bullet" approach that supplements imply, she says.
Despite the lack of evidence – and efforts of popular writers such as Dr Ben Goldacre to debunk the hype – health claims for antioxidant supplements have continued.
In his 2008 book Bad Science, Dr Goldacre describes the antioxidant supplement story as "an excellent example of how wary we should be in blindly following hunches based on laboratory-level and theoretical data." His advice: bin the pills, eat your greens.
Many of the claims for antioxidant supplements promote their "free radical fighting" ability.
But Dr Carolyn Lister from Plant and Food Research says the antioxidant versus free radicals story has been oversimplified: "Free radical doesn't necessarily mean bad and antioxidant doesn't always mean something good."
Free radicals have been shown to be associated with a number of diseases but they also play an important role in controlling body processes. "They may play an important role in stimulating our bodies' repair processes, help fight bacterial infection and act as cellular messengers," she says.
Dr Lister says problems arise when the antioxidant/free radical "see-saw" gets out of balance.
Antioxidant supplements may be one of the things that can upset this balance. Dr Michael Ristow and colleagues from the University of Juna in Germany have theorised that antioxidant supplements may negatively affect the body's own signalling processes and interfere with our "natural" defence systems. However, more research is needed before any conclusive findings can be made.
Much of what's been claimed for antioxidant supplements has been possible because of the lax regulation of the supplement industry. There are signs that may finally be starting to change.
Various health claims for antioxidants have been put on what amounts to a "black list" in the EU. Since December 2012, only pre-approved health claims can be used on products sold there. A suite of claims for antioxidants were rejected after the European Food Safety Authority found they couldn't be substantiated.
Claimed benefits such as antioxidants "protect cells from the harmful effects of free radicals", "protect against oxidation which causes cell damage", and "may help maintain a healthy heart" are among those on the EU’s "non-approved" list. The UK consumer organisation Which? reports that 80 percent of health claims have so far been rejected.
Back here, it's a different story. The existing Dietary Supplement Regulations stipulate that suppliers must not make therapeutic claims for their products. But the regulations aren't routinely enforced and aren't seen as effective in dealing with the burgeoning supplement industry. The maximum fine for breaching the regulations is $500.
Manufacturers can also skirt around the law by making more general claims about their products. The Association of New Zealand Advertisers, which provides a pre-vetting system for therapeutic claims, suggests on its website that phrases such as “provides support for a healthy immune system” would be considered acceptable.
The Ministry of Health has previously acknowledged we're out of step with many OECD countries in failing to regulate natural health products under what it calls an "evidence-based system that can support informed choice and provide assurance about safety and quality".
Legislation to toughen up the regulations is still idling in Parliament. The Natural Health Products Bill will allow health claims to be made for supplements if the claim is on a pre-approved list or able to be substantiated by the product supplier. But details of which claims will get the nod have yet to emerge.
Legislative delays may be good for supplement sales but they're not good for consumers. According to industry data, in the year to January 2013, sales of supplements through supermarkets were worth $85 million. Sales through other outlets mean total revenue will be higher.
The Ministry of Health's Adult Nutrition Survey indicates 30 percent of Kiwis regularly take supplements. A further 17 percent are "occasional" users. According to the survey, the most frequently consumed supplements are oils followed by multi-vitamins and multi-minerals (which include antioxidants).
Supplements may be needed for people with a vitamin or mineral deficiency that can't be fixed by diet. But the overblown claims made for these products – rather than actual health needs – are likely to influence many consumers’ buying decisions. Some people may also be persuaded to take antioxidant supplements "just in case".
But popping a pill hasn't been shown to be an effective insurance policy. The key factors involved in maintaining good health aren't profit generators for the supplement industry: don't smoke, limit your alcohol consumption, exercise regularly and eat a balanced diet.
Report by Jessica Wilson.