As It Turns Out, The Most Hydrating Beverage Might Not Be Water

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Everybody knows that water is vital for life — it makes up about 60% of your body after all — and you'd assume that the best way to get water into your body is by, well, drinking water of course. However, this might not be the case, for although water is a great way to stay hydrated, there's a different everyday beverage that has been shown to be even more effective. A 2016 study published in The American Journal of Clinical Nutrition demonstrated that milk is actually the best beverage to hydrate with, but in order to explain why, you need to know what hydration really is.

Hydration goes beyond simply drinking water. It's about maintaining an exact balance of fluids within and without each cell of the body. Dehydration is a cellular imbalance, which can trigger health issues ranging from a mild dry mouth and dizziness, to severe kidney damage and a deadly loss of blood volume. Proper hydration requires not just consuming water, but also helping your body retain water, and that's where milk can help.

Milk is mostly water — 87% water in fact — so when you drink milk, you are also drinking water. However, the other 13% of what's in milk makes it more hydrating in the long term than water alone. That portion includes a wealth of electrolytes and carbohydrates, and those are the keys to making your body hold onto the water you give it.

You've probably heard of electrolytes in advertisements for sports drinks like Gatorade, but those ads don't provide much information about what they actually are. Electrolytes are a group of minerals distributed throughout tissue and bodily fluids that perform many functions, including helping to maintain the balance of fluids inside and outside of cells. Cow's milk is rich in three key electrolytes: calcium, potassium, and sodium. Cow's milk also contains the hydrate form of the sugar lactose, which provides carbohydrates. Drinks with carbohydrates leave the body slower than drinks without, meaning your body can stay hydrated from milk longer than from water alone.

The 2016 study compared milk, water, and other drinks on a beverage hydration index (BHI). The BHI of each drink depends on how much fluid your body maintains versus how much it loses through your urine. They found that water, soda, coffee, tea, and orange juice all led to about the same amount of fluid loss, but milk led to less fluid loss overall, suggesting it to be the most hydrating beverage of the bunch. It even bested a sports drink.

This isn't the only study that indicates milk is more hydrating than water. Research published in the British Journal of Nutrition in 2007 demonstrated the efficacy of different beverages in rehydrating subjects who had lost 1.8% of their body mass in exercise-induced sweat. It found that milk maintained the body's fluid balance for longer than water or sports drinks, both of which provided only short-term hydration.