A short term side-effect of not enough salt is head-aches and other very real issues. They normally get treated with ibuprofen or other pain killers. Hopefully those who financed the study didn’t know that as that would lead to large conspiracy theories. However like the sugar/fat/calories study of the 1950s there really is a problem with single studies like this getting marketed and over-simplified and messing up generations of nutrition.

Salt is crucial to maintain an adequate blood volume and blood pressure ensuring that our tissues are perfused with the oxygen carrying blood and nutrients