Water Actually Isn't The Best Beverage For Hydration

According to a 2016 study published in The American Journal of Clinical Nutrition, water isn't the best drink for hydration — at least in terms of long-term bodily fluid balance. No, Gatorade isn't either. The answer is actually kind of shocking: it's milk. Both skim and whole milk actually proved more hydrating than water, even with results adjusted for the drink's inherent water content.

How is this possible? Well, hydration involves not just fluid balance, but also retention; meaning the beverage's benefits aren't quickly lost due to urination. Nutrients in milk like fat, lactose (aka milk sugar), and sodium (aka salt) contribute to its ability to stay in the body longer, and thus provide more hydration. Sodium, in particular, is an electrolyte — the body's most common one, according to the Cleveland Clinic — and electrolytes are notably helpful in terms of maintaining our bodily fluid balance.

The study's authors, who hailed from the St. Andrews University School of Medicine in Scotland, developed a methodology for a beverage hydration index. Nearly 90 people participated, and milk's amazing hydrating effects weren't the only surprise revealed by the results, orange juice proved surprisingly hydrating as well.

Proper hydration, of course, is critical for many body functions. We feel better and think better when our bodies are properly hydrated, notes the Harvard School of Public Health, and hydration also plays an important role in maintaining our body temperature, and in providing needed nutrition to our cells. Water, traditionally, is the beverage recommended for this needed hydration.

Indeed, there are daily minimums touted in terms of the water we should drink to stay hydrated. For men, this total is 3.7 liters; for women, 3 liters. Water isn't the only beverage we drink, and other options can also be very useful in helping us stay hydrated. As the Mayo Clinic points out, one of the reasons milk and orange juice are so hydrating is that they're composed mostly of water. Both milk and orange juice, in fact, have a water content of nearly 90%.

Not all beverages are quite so hydrating, however, despite high water contents. Sugary sodas, for example, may seem hydrating in the short term, but they cause water loss long-term. That's because water is needed to help your body process the sugars. Coffee and teas, by contrast, are more hydrating, particularly when a little milk is added to offset caffeine's diuretic qualities. Diuretics, which remove water from the body through frequent urination, can actually be dehydrating, as is the case with alcohol.

In order to measure retention and long-term effects of hydration, the authors of the 2016 study measured the level of hydration two or more hours after beverages were consumed. Both milk (skim and whole) and orange juice proved more hydrating than water by this standard, with better measurements up to four hours after consumption. After adjusting for water content, however, only milk was clearly more hydrating.

"This study tells us much of what we already knew," noted dietician Melissa Majumdar in CNN Health. "Electrolytes — like sodium and potassium — contribute to better hydration, while calories in beverages result in slower gastric emptying and therefore slower release of urination."

That doesn't mean, however, that we should be relying on milk rather than water for the bulk of our hydration. Milk, despite its excellent hydration qualities, also has a lot of calories and carbohydrates. But it can be a great way to recover from high-intensity workouts.

Not only is water not the most efficient beverage in terms of hydration, but it's also possible to drink too much of it. That's because our kidneys can only process so much water each day. In fact, an overabundance of water can actually lead to serious medical issues, per the Mayo Clinic. Typically, the kidneys can process up to 28 liters of water each day, notes Medical News Today. But there's a limit to how much they can get rid of over the course of an hour. So if you drink more than one liter each hour, it's not healthy.

Of course, our hydration levels also need to be balanced with our nutritional levels, and water has the benefit of having zero calories. That's not the case with milk or orange juice, which despite their superb short-term hydration effects, cannot be consumed — at least healthily — in anywhere near the quantity of water. So although water may not be the best beverage for hydration from an efficiency standpoint, it's still the one we should be drinking more than any other, points out UC Davis Health.