I have been forever dealing with people that have problems with edema or just general fluid retention. I have known it has something to do with blood sodium concentration but not the exact mechanism behind it. Here I aim to explain it better and provide a better understanding of why it happens and a possible solution.
ADH (Anti-Diuretic Hormone) is a hormone released in from the pituitary gland that regulates the kidneys reabsorption of water in relation to plasma osmolarity. Plasma osmolarity is the concentration of electrolytes (potassium and sodium primarily) in the blood. We have osmoreceptors that keep very tight measure of this and when the plasma osmolarity increases (too much electrolytes) we release ADH to prevent the kidneys from excreting more water so the concentration decreases to maintain homeostasis. The opposite is true. When plasma osmolarity decreases, ADH should reduce to allow the kidneys to release water. This is how the body keeps control of electrolyte balance.
For some reason, people with edema seem to have a malfunction in the regulation of ADH. They likely have a low concentration of electrolytes, either from not taking enough sodium and potassium or drinking too much fluids, which should have them in a state of low ADH so kidneys can let the fluid out and correct the balance but for some reason they have higher ADH and it is causing the kidneys to reabsorb the fluid keeping the concentration high. The next thing that happens when you can’t correct through urination is the large intestine will stop pulling water out of the stool which could result in diarrhea. I doubt this is happening in people with edema though as they swell and I do believe that ADH would downregulate this action as well. The next thing that happens is the part that causes the edema. Water always wants to flow to a place of higher electrolyte concentration. The blood is can be changed easily but one place that cannot is the intracellular space. This level is maintained pretty constant. So if fluid wants to flow into the cells to get to the higher concentration that means you get all of your cells filling with fluid that cannot escape. That is the definition of fluid retention. The question remains, what can we do about it? I hope to get there by the end of this article.
Something else that causes release of ADH is drop in blood pressure. This explains somewhat why women experience bloating during menstruation. Loss of blood would lower blood pressure and release ADH which would reduce the excretion of water and make you hang onto water. Another thing that causes a release of ADH is nausea and vomiting. If you are feeling nauseated the body shunts out ADH to tell the body that it is about to lose alot of fluid through vomiting so make sure to hang onto any fluid we can so not as to let electrolytes go out of whack.
There is a test you can take with your Doctor to determine the ADH levels. Conveniently enough it is called an ADH test. Another way you can determine if this is an issue is to essentially dry fast for a day to see if your edema goes away and you lose weight. Keep sodium levels as close to normal as you can and restrict fluid as low as possible but to a max of 17oz total. If the edema goes away and you drop a bit of weight it means you may have excess ADH.