Did you ever wonder why drinking sea water would makes us more thirsty and ultimately make you more dehydrated? Sure we all know its because its salty but how does salt relate to water concentration in the body? This theory always rattled me too, until I was finally presented with the scientifically reasoning for it when I studied for a subject at university called human physiology. Alright so lets learn about salt and its role in water concentration in the blood.
First lesson, H20 (a.k.a. water), will always follow sodium (a.k.a.salt), because sodium is positively charged and water is negatively charged, but personally i think its because sodium is cool. Sodium is the coolest little crystallised mineral floating around the body controlling cell membrane excitability, mechanically gated ion channels to open, telling potassium to get out of a cell if it wants to come in and controls whether aldosterone gets to join the party in the body or not.
Okay I just got a bit science nerd exited on you, but you get the point, sodium, is really cool and powerful in the body. It’s so cool that H20 follows it around everywhere trying to be its best friend. So when sodium decides to leave the body through our urine, H20 follows.
Aldosterone is a hormone produced in the cortex of the adrenal glands and acts on the distal convoluted tubule of the kidneys. Aldosterone is also trying to be best friends with sodium because when our sodium levels are low and our potassium levels are high, aldosterone is stimulated to act on the kidneys and draw sodium back into the blood to maintain our electrolyte balance, hence water is retained. Of course Aldosterone is the hero because it saves sodium from being excreted in our urine but H20 is also still proving his loyalty to sodium by following sodium one again.
However you can see that aldosterone is only stimulated to be secreted and save sodium and water from exiting the body when sodium levels are low. if sodium levels are high i.e. if we were to drink lots of sea water, then aldosterone is not stimulated and so sodium leaves the body in our urine and H20 follows suit, therefore we become dehydrated.
Aldosterone is also blocked from being produced and help the body reabsorb salt and water by caffeine and alcohol. This is why alcohol and things that contain caffeine like coffee are diuretics. When consuming these substances our urine becomes clear i.e. dilute because the water and sodium are not being reabsorbed into the blood.
So you can see that if sodium levels are too high or too low we can get hydration issues.