Tech + Health


When Table Salt Becomes Poison

Lacey Spears is accused of killing her son by poisoning him with salt. What actually happens to the body when a common ingredient becomes fatal?

There are some kinds of human depravity that I will never truly understand. While I may oppose or abhor various forms of violence or crime, in many cases I can reason through how people can be driven to engage in them. But some are beyond my capacity to truly grasp.

Nothing defeats my powers of comprehension like the deliberate harm of a child.

Reading about the case of Lacey Spears, a woman recently arrested on suspicion of killing her son with overdoses of salt, I once again confronted a situation where the malevolence or unfathomable sickness of another individual confounded me utterly. If she is proved to have committed the crime of which she stands accused, it baffles me as a human being, to say nothing of being my being a parent and a pediatrician.

While her motivations may permanently defy explanation, her methods are easier to analyze. Salt probably doesn’t strike most people as a potential poison, which may well have been her rationale for using it. Indeed, under most circumstances it would be ineffective to try poisoning someone with it. But the specifics of her son’s situation made it possible.

Salt (or, more specifically, sodium) excess goes by the medical term “hypernatremia.” Simply put, this is when the balance of sodium and water in a person’s body tips dangerously toward the former. There are a variety of causes. The ones I’ve encountered were due to massive diarrhea in patients vomiting too much to replace the water loss, or those getting IV fluids where their sodium needs weren’t properly calculated and they were given too much.

Simply put, if there is too much sodium outside the brain cells, water will flow out to right this discrepancy, causing the cells to shrink.

The ill effects of hypernatremia are primarily caused by cell shrinkage and damage in the brain. Our fluids and electrolytes occupy different spaces within our bodies, both inside and outside our cells. When there is an imbalance between water and chemical levels (“osmolality”) in one space and another, the laws of chemistry require water to move such that balance is restored. Simply put, if there is too much sodium outside the brain cells, water will flow out to right this discrepancy, causing the cells to shrink. Confusion, jitteriness, seizures, coma, and death can result if things aren’t corrected.

The reason normal, healthy people can’t be effectively poisoned with sodium is that we get thirsty. Once a threshold osmolality is reached in our bodies, it triggers our brains to make us seek water. (Brain damage to the centers responsible for this can also cause hypernatremia.) Assuming we have access to water and can keep it down, it solves the problem.

But Spears’ son Garnett was tube fed. I don’t know the details of his case beyond what has been reported, so I don’t know what capacity (if any) he had to take in fluids by mouth. If his ability to drink was absent or too limited to compensate for massive amounts of sodium given in his feeding tube, he could be effectively poisoned with it. Presumably his mother thought it would go undetected because of how peculiar and specific the circumstances of its use for this evil purpose.

The “how” of Spears’ alleged crime make sense once the basic physiology of thirst and electrolyte balance are understood. It was probably relatively easy to accomplish. What remains beyond reach, forever, is why.