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SKEPTOID BLOG:

Yes, the Dose Really Does Make the Poison

by Alison Hudson

November 10, 2014

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Donate One thing that frustrates me in conversations about "harmful chemicals" on Skeptoid and elsewhere is when individuals display a complete lack of understanding of dosage. This comes in two forms.

The first form is the passive argument that completely omits"dosage" from their point entirely. I can never tell if someone overlooking dosage is being uninformed or dishonest; part of me wants to give the benefit of the doubt, but another part of me finds it hard to believe they've never encountered such a basic concept as dosage. The second is the active argument that "Dosage doesn't matter" or "dosage is irrelevant", which is often used to imply that some chemical or other is so bad that is always should be avoided. Invariably this is directed at some chemical that millions of people ingest everyday without obvious harm.

Both of these arguments fall flat in the face of scrutiny. Dosage very much matters, because all chemicals are toxic. This is not a sweeping generalization; it's just a basic fact of chemistry. Toxic is a word you hear people throwing around a lot without any actual sense of definition or context, i.e. "toxic chemicals", but there is no such thing as a "non-toxic chemical"; everything is a chemical and all chemicals have a point where they become toxic to the human body.

The term for the dose at which a chemical becomes dangerous or deadly is toxicity. In chemistry they also refer to a chemical's "lowest published toxic dose", or Toxic Dose Low (TDL), the point at which a chemical will start to have adverse effects on the body. The point at which a chemical becomes toxic enough to kill is called its Lethal Dose Low (LDL). Every chemical has a TDL and a LDL, though the levels vary greatly from chemical to chemical.

Consider water, the most common and important ingredient in the things we consume. In debates about chemicals we skeptics love to bring up water (which irritates the toxic chemicals crowd to no end) because it's an extreme and obvious illustration of the point: water, in large enough quantities, can kill. It has both a TDL and a LDL. And no, I'm not talking about drowning; I'm talking about water intoxication, which can kill you. And yet we drink it every single day.

Some chemicals have TDL so low that they are almost never safe. An example would be cyanide. Compounds of cyanide are mostly useless in medicine because their TDL and LDL are so low. They also don't generate a very useful medical effect even below toxic levels, though even cyanide has been used in medicine in the past. Still, trace amounts of cyanide occur in many natural foods. We eat it every single day. Unless one is inclined to eat apple seeds as a pastime activity, however, they have nothing to fear.

Other chemicals have LDL so high that they are only hypothetically lethal. Ascorbic acid (commonly known as vitamin C) is a popular supplement and it's a vital part of our bodily function. It is difficult for a human being to bring ascorbic acid to TDL, as ascorbic acid is water-soluble and flushes out of the body quickly. But even this popular supplement can cause bodily discomfort (diarrhea, vomiting, stomach cramps) when taken in significantly large dosages. It also has a LDL, though that level can probably only be achieved in very rare, unusual circumstances.

Ultimately, every chemical has TDL and LDL levels. And everything is a chemical. Therefore every chemical is a "toxic chemical," and toxicity relies on dosage. There's honestly no way to argue the point. So why do people insist on arguing it? If you're going to try and convince me that some food additive or popular drink is "toxic", be ready to cite dosage if you want me to take you seriously.

And because I can't type the word toxicity that many times without getting the song stuck in my head, here's a little System of a Down as a treat for making it to the end.

by Alison Hudson

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