Two published studies in JCI might change how we think the body handles “too much salt”
What we learnt in medical school:
If you eat a lot of salt — sodium chloride — you will become thirsty and drink water, diluting your blood enough to maintain the proper concentration of sodium. Ultimately you will excrete much of the excess salt and water in urine.
When salt intake was increased in Russian cosmonauts studied, the urine Na excretion did increase as expected. But, the urine volume was not associated with those changes. When salt intake was high, the folks drank less water in the long run and still excreted increased water amounts. Where was this extra water coming from? The crew members were increasing production of glucocorticoid hormones, which influence both metabolism and immune function and allowed fat breakdown leading to water production.
Taking these observations to the lab, the investigators began a study of mice in the laboratory. The more salt the investigators added to the animals’ diet, the less water the mice drank(counter to what we think science teaches us when we eat a high salt diet). The animals were getting water by not drinking it but via increased levels of glucocorticoid hormones breaking down fat and muscle in their own bodies. This freed up water for the body to use.
Now published, the authors report the unexpected observation that long-term high salt intake did not increase water consumption in humans but instead increased water retention. Moreover, salt and water balance was influenced by glucocorticoid and mineralocorticoid fluctuations.
This leads to a even bigger question? – does high salt intake= potential weight loss as fat breakdown is happening? So in other words, a high salt intake body is behaving similar to a starving body.
I am sure that there is more to it! In the long run, this is probably not a good adaption of the body and high glucocorticoid state is likely a risk of diabetes. But these studies show us that we really don’t understand salt homeostasis in humans as we thought we did.
Bravo to the scientists on publishing this alternate view on salt intake and water production.