Would drinking normal saline help with hydration?

Question

In my first aid kit I carry* sterile normal saline for wound and eye irrigation (most often used for the latter). Can you drink it? Would it help with hydration? It's nominally isotonic with blood serum, but I'm not sure what effect it would have if consumed.

What got me thinking was a slight planning error in obtaining water on a bike ride on Sunday. It was nothing serious but I was a little dehydrated with only a mouthful or two left in my bottle before I found anywhere to get more water up and I was starting to worry. I tend not to finish the last bit in my bottle unless I really have to, saving it in case of things like dust/insects caught in my throat.

* _{only 2×40ml vials in my light (cycling) kit but in some situations I might have more, so I'm thinking about concentration not quantity}

Answer 1

Yes, you can drink it. Saline of this sort (0.9%, 9 g/L or about 150 millimol/litre or 300 milliosmol/litre) is known as an isotonic solution as the salt concentration is the same as that in the body (iso = same, tonic = ability to move solution into or out of cell). There are a whole class of sports drinks known as isotonic drinks, which are used for hydration and mineral replacement (sodium etc from sweating).

In addition there is a class of sports drinks that are hypertonic (more salty than the body), which are used to replace carbohydrates (sugars) and salts in the body, but must be used with another hydrating drink or you will get dehydrated.

There are also hypotonic drinks, which I guess includes water. These are drinks with less salt than the body and are hydrating, but may not do much in mineral replacement.

I found a good site with decent explanations of the respective drinks and their uses at Diabetes.co.uk/sports-drinks