Toxicologists have a saying that "the dose makes the poison," meaning that anything and everything can kill you in large enough quantities. So here we take five incredibly common (and usually benign) foods and household items to their illogical conclusion. Ever contemplated eating 480 bananas? Don't do it.
While we're on that note, this isn't a dare. Also, drinking that much coffee sounds disgusting.
Let us ignore, for now, the logistical difficulties of fitting 480 bananas in our stomach, and talk about potassium. A typical banana contains about 450 milligrams of potassium, making it an excellent source of the electrolyte. Potassium ions flow through our bodies, maintaining the balance of fluid inside and playing a role in muscle contractions and nerve impulses. Cells in virtually every tissue in the body have potassium channels.
It would be virtually impossible to eat a median lethal dose of potassium (about 1.4 pounds), but the element is a lot more deadly injected directly into the bloodstream, when a massive and sudden influx overwhelms the body. We know this all too well because in lethal injections, potassium chloride is the final chemical that stops the heart from beating.
A moderate dose of caffeine is a much-needed pick-me-up in the mornings. A very high dose of caffeine is caffeine intoxication, the worst parts of drinking coffee exacerbated: restlessness, anxiety, insomnia, an upset stomach, a racing heart. Take that to an even further extreme and caffeine can overstimulate the nervous system so much that it causes a cardiac dysrhythmia (irregular heartbeat) or seizure.
A median lethal dose is about 11 grams for an adult. Caffeine poisoning is extremely rare and unlikely with coffee alone, but the advent of pills and caffeine-laced energy drinks have made the problem worse.
As any reader of castaway survivor stories will know, do not drink the seawater. There is far too much salt in it for our bodies to handle.
Like potassium, sodium is an electrolyte that regulates the water flowing in and out of our cells. When there is too much sodium in the interstitial fluid that bathes our cells, water will naturally leave those cells by osmosis to restore the balance. This causes the cells to shrink. The most obvious symptoms of hypernatremia, or an excess of salt, are neurological: unresponsiveness, lethargy, weakness. Too much salt, and it can cause seizures or a coma.
Yes, even water. Water intoxication is essentially the opposite of too much salt. When there is too much water and not enough salt in the interstitial fluid between our cells, those cells start taking in water and swell up like balloons. Tightly packed brain cells have no room to swell inside the skull, leading to brain damage that could be fatal.
Drinking that sheer amount of water is rare under normal circumstances. It is most common in endurance athletes or ravers taking ecstasy, where the sweating leads to a lot of water drinking. But electrolytes lost through sweat also need to be replaced. Our bodies generally do a good job of maintaining a water balance between all that sweating, peeing, eating, and drinking, but it physically breaks down at the extremes—specifically, 17 16-ounce bottles.
Every tube of toothpaste comes with a warning: "Keep out of reach of children under 6 years of age." Fluoride in small doses is indisputably good for preventing cavities, but too much of it can necessitate a call to the Poison Control center. Still, a deadly dose requires a lot of toothpaste—24 6-ounce tubes for an adult and multiple tubes even for a small child. A review of 87 fluoride ingestion cases in children found none with lasting effects that were the result of eating toothpaste.
Illustrations by Michael Hession
A Brief Note on Methodology
All numbers are calculated using a standard metric called median lethal dose (LD50), the dose that kills half of a tested population. This accounts for natural variability between subjects, but it also means that even a dose below the LD50 can be lethal. LD50s are usually tested in rats or mice and reported as milligrams of substance per kilogram of body weight. These numbers are calculated for a 90 kg (approximately 200 lb) adult human male and are, of course, only estimates. Again, don't take this as a dare.
Here are the sources for the LD50s and other relevant numbers.
Bananas: Potassium citrate, which is the form of potassium in bananas, has an LD50 of 7200mg/kg. About 1/3 of the molecular weight of potassium citrate is from the potassium, so a banana that contains 450 mg of potassium contains 1350 mg of potassium citrate.
Water: Water has an LD50 of 90 ml/kg.