The naturalistic fallacy – the notion that all things natural are good (and therefore the unnatural must be bad) is pervasive in our culture, and quite dangerous when applied to medicine. In the context of food and medicine an unhealthy reverence for nature takes the form of assuming that something which is natural must be magically safe and effective. Of course, nature does not care about us and it is more often toxic and deadly than helpful.

In the US the word “natural” is used as a marketing ploy to convey a sense that a product is good and wholesome. This is combined with a terribly unscientific scheme for categorizing foods vs drugs vs supplements and regulating health claims about them. The end result is that the public is being sold many drugs as if they were vitamins, and worse the drugs are largely unknown, unstudied, not purified, may contain contaminants, and have highly variable doses of whatever happens to be in them. Even worse, just about any health claim can be made for these nostrums as long as the company is slightly careful about their wording (really, all they have to do is avoid making specific disease claims – a trivial obstacle for any marketing executive worth his salt).

The latest example of this situation is the discovery that popular herbal kelp supplements are contaminated with arsenic. A study led by UC Davis public health expert Marc Schenker found higher than safe levels of arsenic in 8 out of 9 over-the-counter herbal kelp products they studied.

The study was prompted by the case of a 54-year-old woman who was seen at the UC Davis Occupational Medicine Clinic following a two-year history of worsening alopecia (hair loss), fatigue and memory loss, which ultimately was attributed to chronic arsenic poisoning from the kelp supplement she was taking to promote her health and vigor.

It may seem that an adequate solution to this type of problem is better regulation to ensure purity in supplements – and admittedly this would be a good start. But the real problem is deeper. All health intervention is properly assessed by a risk vs benefit analysis. The supplement industry is largely selling products without any proven benefit. There are specific vitamins that have been proven to be beneficial for specific indications (folic acid to prevent spina bifida, for example). But these legitimate and evidence-based uses are a small minority of the industry. So with a benefit of zero, any risk would entail an unacceptable risk vs benefit ratio.

Although risk can be minimized with better practices and regulation, it can never be reduced to zero. This means that there has to be some reasonable evidence for benefit in order to justify the intervention at all. If the occasional arsenic poisoning occurred as a consequence of a health intervention with demonstrable benefits to well-being and survival, then that would be reasonable. Kelp supplements are little more than snake oil – so even a single arsenic poisoning is not worth it (never mind the wasted health dollars on useless products).

This kind of assessment contrasts to the common response of “it can’t hurt,” or “what have I got to lose.” This reflects a basic human psychology – we worry more about missing out on a benefit than we do losing something we already have (witness the lottery). Likewise, people worry more about not getting the health benefit from taking the magic pill than they do about a possible negative outcome – as long as they are lulled with some assurance, like the fact that the product is all natural.

Rather than playing the lottery with health care, we need rational risk vs benefit analysis based upon carefully collected evidence. It would be nice too if government regulations reflected this sensible approach.