In recent months, I’ve made a new CF friend on Twitter, @nanosmakemepuke, who just so happens to be a chemist with a Tumblr blog with a name that immediately gave me a source to go to for an expert answer to my ongoing query. I got the bright idea this week, “Who better to ask for an explanation of why cystic fibrosis patients need more salt than normal people than Amanda? She’s got a PhD in chemistry!” So I did, and she obliged with a pretty detailed reason in layman’s terms that I think you’ll find as fantastic as I did. Many, many thanks for such a great piece that will live on for a very long time to help educate others looking for the answer to the same question that has been bugging me for years.

Amanda: Salt is the combination of sodium and chloride. The biochemical processes that go on in our bodies are such that only a very narrow range of salinity (concentration of salt in our body’s fluids) is acceptable. Too little or too much is literally a matter of life and death. Fortunately, our bodies are really good at ensuring that it contains the ideal concentration of salt by adjusting the volume of fluid in our blood and tissue so that the salinity is always in the ideal range. If you have too much salt you become thirsty, causing you to drink water, which dilutes the too-high concentration of salt in your body. If you have too little, you usually crave and eat something salty.

In cystic fibrosis, improper transport of chloride (a component of salt) causes all the horrible symptoms and manifestations of this disease. CF bodies don’t fully regulate the concentration of salt within the cells that line our airways, digestive tract, and skin, causing the concentrations to be a bit out of whack—either too low or too high, depending on which side of the cell you’re looking at. In the case of the cells that create sweat in a CF patient’s sweat glands, they leave too much chloride inside the “sweat reservoir,” which must in turn be balanced with an equivalent amount of sodium (wherever chloride goes, sodium follows), making the super-salty sweat characteristic of cystic fibrosis.

Every time a CF person sweats, their body loses up to 10 times the amount of salt a normal healthy person would in the same amount of sweat. That means excessive sweating (as might happen in the summer or when exercising) puts people with CF at a much higher risk of dehydration than other people. Because of this salt loss, people with CF must be very diligent to replace lost salt whenever they sweat, otherwise there is a risk of suffering from dehydration.

Generally speaking, people with CF need to include salt as a regular part of their diet to compensate for abnormal amounts of salt lost through sweat. The usual reason doctors recommend a low-salt diet for non-CF people is so that they don’t develop high blood pressure, which causes your body to retain more fluid in your blood to compensate for the excessively high concentration. If you have CF and have high blood pressure, obviously the amount of salt in your diet is something you need to discuss with your doctor.

Bottom line: it’s important for people with CF to add a little extra salt into their diet in order to avoid dehydration in warm weather and when exercising. Also, always make sure you consume something salty with plenty of fluids so your body can process it properly.