Our diet is woefully inadequate, and puts us at risk from illnesses such as cardiovascular disease and cancer. Or so the dietary supplement industry would have us believe. Two Wageningen professors take up the cudgels.
It is hardly surprising that consumers have a hard time finding their way through the forest of contradictory claims and advice.
Saskia Geurts, director of NPN, an association of producers and wholesalers of dietary supplements, believes the products do offer a useful addition to our diet, and can contribute to good health. 'The recommended daily amount (RDA) is often based on the prevention of deficiencies, whereas it is not enough for optimal health', she claims. 'What supplements you need, and how much, varies per person, which makes a multivitamin a good choice for everyone.'
Dr. Ellen Kampman, professor of Diet and Cancer, thinks the claim that the RDA is too low is oversimplified: 'There is no basis for this. The RDA established by the Health Council is set at an amount that is enough for almost everyone, even those who need a lot. It includes quite a wide margin. People who stick to the RDAs will certainly get enough of a nutriet. There are just a few people who may need more. But for most people, even a bit less than the RDA is enough.' Kampman says that whether you should advise dietary supplements depends a lot of the population group you have in mind. 'You can never tar the whole population with the same brush', she explains. 'For example, I advise elderly people to take a vitamin D supplement, as their bodies cannot make it themselves so efficiently anymore. But this advice certainly doesn't apply to everyone.'
Kampman claims that there are big industrial interests at stake in the dietary supplements, but that the claimed health benefits are not based on sound science. One problem is that only a tiny percentage of the Dutch population get the recommended amount of vegetables, and about ten percent eat enough fruit. Kampman: 'The question is whether we should solve this with supplementation or by taking steps to stimulate consumption of fruit and vegetables.'
Dr. Renger Witkamp, professor of Nutrition and Pharmacology, thinks along the same lines. He says supplements have become a sort of safety valve for modern society: you can eat all the wrong foods and then make up for it with pills and potions. That gives us a clean conscience. Witkamp is positive but critical about dietary supplements. He thinks most use of supplements is based on emotions. 'Pill-poppers are believers', he says. He has his doubts about the effectiveness of some supplements: 'The industry has given little prove up to now'. And yet he agrees with Geurts to some extent. 'The supplement industry does have a point. Not many people eat healthily. On the other hand, a lot of things are still unclear, especially on the subject of antioxidants.'
Hard evidence that supplements work is thin on the ground. But that didn't stop the NPN from putting out a press release in August, after the publication of the Nature study, saying that a lot of research has demonstrated the effectiveness of antioxidants against cancer. Witkamps thinks this is far too hard a claim. In his view there is still very little solid scientific evidence for the protective effects of antioxidants. 'There are just a few positive effects shown in in-vitro studies', he explains. Kampman agrees. 'There are very few human studies that convincingly prove the effect of antioxidants.'
On the other hand, Kampman says, the positive effects of eating fruit and vegetables have been proven: 'The assumption is often made that those effects can be put down to the antioxidants they contain, but that is not necessarily the case. Quite different nutrients, perhaps in a particular combination, might be responsible for the effects.' The World Cancer Research Fund also advises against taking antioxidant supplements until more scientific data is available. A varied diet with enough plant-based products is better.
The claims of the supplement industry have not gone unnoticed by the European Food Safety Authority (EFSA). This advisory body on food safety keeps an eye on health claims on packaging. ''I am afraid that the EFSA looks at the proof for health claims as if we were talking about medicines', says Geurts of the NPN. 'The effects of supplements are much more subtle than those of medicines, and are therefore harder to measure.' Geurts pleads for a more subtle approach to the EFSA's assessments, so that likely effects are also communicated to the consumer. 'If folic acid, which can prevent spina bifida in babies, had been assessed by the EFAS ten years ago, it would never have passed, even though the effect was already considered extremely likely then.'
P.S. The most popular supplements
Carotene-like substances have an antioxidating effect and are needed for making vitamin A, among other things. Although people eating a diet rich in carotene (from fruit and vegetables) are relatively healthy, recent research suggests that taking carotene as a supplement is probably not beneficial.
Folic acid (vitamin B11) is an essential supplement for pregnant women due to its beneficial effects on the development of the foetus. It has been proven to help prevent spina bifida.
Vitamin C is probably the best-known antioxidant. There is plenty of this vitamin in fruit and vegetables. Kampman: 'Any excess just comes out in your pee; which makes it quite an expensive pee. I think an orange is healthier than pills.'
Vitamin D: along with folic acid, this is one of the few supplements for which clear recommendations exist. This vitamin is vital for bone growth. Deficiencies can be determined with a blood test.
Probiotica drinks full of live bacteria are used to combat certain intestinal complaints. Kampmans says the claims that they strengthen the immune system are premature, to say the least. 'There are few human experiments that support this claim that they increase resistance.'
Vitamin E-like substances are present in vegetable oils and are swallowed by the barrel as antioxidants, yet there is little clarity as to whether and how these substances work as antioxidants. According to Kampman, they could increase the risks of prostate cancer.
Polyphenols are antioxidants that are found in coffee, tea and red wine, as well as in fruit and vegetables. They are claimed to be effective against cancer and cardiovascular disease, among other things. But for the time being there is little evidence that these substances have positive effects on the human body.
Glucosamine is found naturally in the human body, and is needed for making cartillage in the joints. As a supplement it is said to help repair the damage caused by arthritis. Scientific evidence for this is still problematic.
Fish oils, particularly the omega 3 fatty acids in them, are healthy. They lower cholesterol, have an anti-inflammatory effect, and numerous studies have pointed to their effectiveness against cancer. Kampman does not know of any negative effects of this supplement, and yet she finds the positive effects disappointing. 'I think it is better to eat oily fish a bit more often. That way you not only get the good fatty acids, but also vitamin D and selenium.'