Some plant-based nutritional supplements contain dangerous levels of carcinogenic substances. The result suggests that stricter regulation is needed.
This finding has come out of research by Suzanne van den Berg, a researcher in the Toxicology chair group. Van den Berg calculated the doses of substances known as alkylbenzenes that people ingest through these supplements. She then compared them with the dose at which liver cancer occurs in animal tests. Her results were published early in December in the journal Food and Nutrition Sciences.
The toxicologist researched supplements that can be bought over the counter at chemists, pharmacies and on the internet. Many of these are tablets or oils based on basil, fennel, nutmeg, sassafras or calamus. Even though specific health effects have been described, none of these supplements have yet been positively evaluated by the European Food Agency EFSA. Moreover, very little is known about the possible dangers of these remedies.
Van den Berg researched the impact of four substances known as alkenylbenzenes, the concentration of which appears to vary widely. Some supplements contain low, safe levels of them while others contain massive doses. Van den Berg: 'In oils from basil concentrates, the concentration of estragole ranges from 0.11 to 85 percent.'
In order to establish which concentrations are dangerous for humans, Van den Berg looked at earlier publications on the effect on rats, which show which daily dose is enough to cause 10 percent more rats than average to go down with cancer. This data cannot be applied directly to human beings of course. To ensure safety, the dose given to humans has to be much smaller. 'According to the rules in toxicology, the ratio between the dose that causes 10 percent more cancer in lab animals and the daily dose for humans should be at least 1 to 10,000', says Van den Berg. The figure is so big because it takes into account differences between people and animals and among people.
So some supplements contain such high levels of alkenylbenzenes that they represent a danger to consumers, even when the recommended dosages are followed. 'People think: it is natural so it is safe', says Van den Berg. 'But that is by no means always the case.'
The researchers do have reservations about their findings. The research is largely based on animal studies which study the effects of pure alkenylbenzenes, whereas the supplements contain other components as well. 'That can lower the risks', says Van den Berg. 'There are recent results from our research that show that the negative effect is lower through the interaction with other botanical components.' Further research should cast more light on this aspect.
Nevertheless, a European Commission report of 2008 shows that the market for supplements (including plant-based ones) grew across Europe in the period 1997-2005, and is still growing. A striking detail is that plant-based supplements are very popular in the Netherlands, with a market share of 75 percent. RR