Salt poisoning

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Salt poisoning happens when you take in too much sodium, usually from salt (sodium chloride) or salty liquids. It is rare for it to cause severe problems, and lethal cases are even rarer.

- Lethal dose: about 0.5–1 gram of table salt per kilogram of body weight.
- Most often seen in children who are made to eat too much salt. Adults can be exposed by drinking seawater, brine, or eating a lot of salty foods like pickles or soy sauce. It can occur in people with mental health problems. Animals can be affected too, especially pigs, cattle, and poultry.

Symptoms come from high sodium in the blood (hypernatremia): thirst, weakness, nausea, and loss of appetite at first; later, confusion, muscle twitching, seizures, or coma. Brain swelling can be fatal if not treated.

Normal blood sodium is about 135–145 mEq/L. Severe symptoms usually occur when it rises above around 160 mEq/L.

Why seawater is dangerous: seawater is much saltier than the kidneys can handle. Drinking it raises blood sodium and causes the body to lose more water in an attempt to get rid of the salt, which can lead to seizures or heart problems. In life-raft scenarios, drinking seawater greatly increases the chance of death (about 39% vs 3% for those who don’t drink it).

Some sea birds and other marine animals can drink seawater safely, but humans cannot.

A small amount of seawater taken by accident is not usually harmful if you drink fresh water afterward, but using seawater to stay hydrated is counterproductive.

Historical note: during droughts, sailors facing scarce fresh water sometimes considered seawater as a last resort, a choice that could worsen illness.