I was already planning on doing an article this week on the misconception that anything “natural” must be safe (and conversely something that isn’t natural must be harmful) when this news story broke: “alternative medicine” practitioner and promoter of “natural” remedies Gary Null is suing the manufacturer of one of his own dubious health supplements, claiming it nearly killed him because they put too much vitamin D in it (despite the fact that Null regularly recommends vitamin mega-dosing – the irony is almost overwhelming). But vitamin D is natural and good for you – how can it have almost killed him?
Any toxicologist learns pretty quickly that the “dose makes the poison” (generally attributed to Paracelsus, the father of toxicology), and that pretty much everything is toxic at some dose, even if beneficial at lower doses – much of the work of a toxicologist involves determining at just what dose a substance may have harmful effects.
These rules apply to natural substances as well as synthetic chemicals, and in fact a natural substance is just as likely to be toxic as a synthetic chemical. The most toxic substance known (i.e. the substance that requires the smallest dose to be lethal) is botulinum toxin, which is a natural substance produced by the bacteria Clostridium botulinum. Interestingly, despite being so toxic, it also apparently has some therapeutic uses, as well as being the key ingredient of botox, at even lower doses. Other “natural” substances include lead, arsenic, cyanide, benzene and benzo(a)pyrene (pretty much the “classic” carcinogen).
Part of the recent trend towards “organic” foods is related to the use of pesticides. Even though the amount of synthetic pesticides on food is regulated based on toxicological data, many people prefer fruits and vegetables which have not been exposed to synthetic pesticides. What a lot of people don’t realize is that plants produce their own pesticides to defend against insects as well;one study estimated that 99.9% of total dietary pesticide intake is natural pesticides produced by the plants themselves. Very few of these natural pesticides have been studied, but of those that have about half have been carcinogenic in rodent studies. It’s likely that the hazards of synthetic pesticides are insignificant compared to the hazards of the natural pesticides already present in plants – especially when you consider that synthetic pesticides used on food crops have been studied and are only allowed if it can be demonstrated that the residues meet safe limits, while plant-produced pesticides are generally of unknown toxicity to humans and there’s no reason to expect them to be non-hazardous (though obviously plants that are acutely toxic are generally not grown as food crops). I’ve even heard it suggested that the natural pesticides may be produced at higher concentrations in organically grown plants in some cases, to offset the lack of protection from synthetic pesticides – unfortunately I don’t have a public domain reference for this claim, though intuitively it makes sense. Furthermore, some pesticides can be used on organic crops – they just have to be “natural” pesticides, which aren’t necessarily less toxic to humans than synthetic pesticides.
In addition to natural pesticides, plants may contain other toxic chemicals, either as part of their biochemistry or which they take up from the soil (e.g. toxic metals – again “natural”, even if concentrations are often elevated due to human activity). After harvesting, bacteria or mould can produce additional toxins if foods are not properly stored or prepared. In particular, aflatoxin, which is produced by a type of mould, is a fairly potent liver carcinogen which has been found in the food supply.
Cooking foods, particularly at high temperatures, can produce polycyclic aromatic hydrocarbons (PAH), including benzo(a)pyrene and other carcinogenic PAH, at toxic levels (particularly if there is actual “charring) – these are again naturally occurring substances.
Coming back to the Gary Null case described at the beginning of this entry – as you are doubtless aware, vitamin D has a lot of beneficial effects (newspapers are regularly reporting on new studies touting various conditions it may help prevent). Vitamin D deficiency can be fairly common in people living in high latitudes (i.e. where I live) – the main source is from sunlight exposure, and up here most people don’t see the sun very much over the winter. However, very high doses (>1000 ug/day or 40,000 IU/day) are toxic, resulting in elevated calcium levels in blood, eventually leading to a host of other effects, including potential kidney failure.
Other vitamins have also been associated with a variety of toxic effects at high doses, particularly fat-soluble vitamins. Furthermore, many vitamins interact with key metabolic enzymes (known as cytochrome P450 enzymes), increasing or decreasing their activity; these enzymes play a large role in the metabolism of toxic substances, and can either increase or decrease their toxicity, depending on the specific mechanism by which the toxic chemical works. As a result, in addition to the potential toxicity of vitamins on their own at high doses, they can affect the toxicity of other substances you are exposed to.
In summary, assuming that a substance is safe just because it is “natural” is incorrect. This applies to organic fruits and vegetables, “natural” health products, vitamins, and anything else we are exposed to. You have to look at each chemical on its own merits, regardless of whether it is natural or synthetic. Unfortunately, toxicity data on naturally occurring chemicals is often lacking, since there is no manufacturer responsible for establishing the safety of the chemical.