Milk Hydrates Better Than Water: Are Beer and Coffee Hydrating Too?

When it comes to hydration, water often takes the spotlight. It's calorie-free, widely available, and heavily marketed as the best way to quench your thirst and replenish your body’s fluid levels. However, emerging scientific insights suggest that water might not always be the most effective hydrator. Surprising new findings reveal that milk — yes, regular cow’s milk — can actually be more hydrating than water. But what about other popular beverages like beer or coffee? Can they contribute to hydration, or do they do more harm than good?

Let’s dive into the science behind hydration, and find out what truly quenches our thirst and keeps our bodies functioning at their best.

The Science Behind Hydration: It’s More Than Just Water

A recent study conducted by researchers at the University of St Andrews in Scotland challenged the long-standing belief that plain water is the gold standard for hydration. According to the research, while plain still or sparkling water is indeed effective at quickly hydrating the body, drinks that contain small amounts of sugar, fat, or protein may be even better — especially for maintaining hydration over a longer period.

Dr. Ronald Maughan, a professor at the University of St Andrews School of Medicine and lead author of the study, explains that this is due to how the body processes different beverages. The volume of fluid consumed, along with its nutritional composition, affects how quickly it leaves the stomach and enters the bloodstream. The more nutrients — such as sugars, fats, or proteins — a drink contains, the slower it empties from the stomach. This slower digestion allows the body to absorb water more gradually, keeping hydration levels stable for longer.

Why Milk is a Superior Hydrator

Based on this mechanism, milk has emerged as a particularly hydrating beverage. Unlike water, milk contains lactose (a natural sugar), modest amounts of fat and protein, and important electrolytes such as sodium and potassium. This combination makes milk more effective at both immediate and long-lasting hydration.

Milk’s sodium content also plays a crucial role. Sodium helps the body retain fluid by reducing urine output, effectively locking in hydration. This mechanism is similar to that used in oral rehydration solutions (ORS), which are used to treat dehydration caused by diarrhea. ORS formulas include small amounts of sugar, sodium, and potassium to help the body retain more fluid.

Melissa Majumdar, a registered dietitian and spokesperson for the Academy of Nutrition and Dietetics, who was not involved in the study, points out that these findings support what experts have long believed: electrolytes like sodium and potassium improve fluid retention, and calories in drinks slow stomach emptying, reducing fluid loss via urine.

So, the next time you’re reaching for a drink after a workout or a long day in the sun, consider a glass of milk — it might do a better job than water alone.

The Catch: Too Much Sugar Backfires

While drinks with some sugar and nutrients can help with hydration, not all sugary beverages are equal. Beverages with a high sugar content, such as soda or concentrated fruit juices, might actually hinder hydration in some situations.

Here’s why: once these sugary beverages reach the small intestine, their high concentration of sugar needs to be diluted before the body can absorb them. This triggers a process called osmosis, during which water is drawn from surrounding body tissues into the intestine to dilute the sugar. However, because the water pulled into the intestine hasn’t technically been absorbed yet, this process can result in a net loss of body water — the opposite of what you want.

Furthermore, sugary drinks like soda and juice come with added calories and little satiety. Unlike solid food, they don’t make you feel full, potentially leading to excess calorie intake without a sense of satisfaction.

In short, beverages with moderate sugar content can be hydrating, but too much sugar undermines the benefits — and may even contribute to dehydration under certain conditions.
Is Coffee Dehydrating?

Coffee has long been accused of being a diuretic — a drink that makes you urinate more and lose fluids. But is that reputation deserved?

The answer lies in the dosage. A standard cup of coffee with about 80 mg of caffeine actually hydrates the body nearly as effectively as water. While caffeine has a mild diuretic effect, this only becomes significant when consumed in large amounts — typically over 300 mg, or about 3 to 4 cups of coffee.

Interestingly, habitual coffee drinkers tend to develop a tolerance to caffeine's diuretic effect. And adding a small amount of milk to coffee can further diminish any negative impact by slowing the release of caffeine and adding some nutrients to the beverage.

So yes, your morning latte can contribute to your daily fluid intake — especially if you’re not overdoing it.

Beer: Friend or Foe of Hydration?

When it comes to alcohol and hydration, things get more complicated. Alcohol is a well-known diuretic. It inhibits the release of vasopressin, an antidiuretic hormone, which causes your kidneys to excrete more water than usual. This is why alcohol consumption often leads to frequent urination — and eventually, dehydration.

However, not all alcoholic beverages are created equal. Dr. Maughan notes that beer, being lower in alcohol content and higher in water volume compared to spirits like whiskey, causes less fluid loss. In other words, a pint of beer might be less dehydrating than a shot of liquor, simply because you're consuming more water along with a lower dose of alcohol.

That said, beer shouldn’t be your go-to hydration method. The dehydrating effects of alcohol still outweigh any minor hydration from the water content. Plus, alcohol impairs cognitive and physical performance, especially in the heat or during exercise — precisely when you need hydration the most.

Beyond Beverages: Food and Hydration

It’s important to remember that we get a significant portion of our daily fluid intake from food. Fruits and vegetables like cucumbers, watermelon, strawberries, oranges, and lettuce are composed primarily of water and contribute to hydration.

Soups, stews, and yogurt are also high in water content and can help maintain fluid balance, especially in people who don’t drink large volumes of fluids throughout the day.

The key takeaway? Hydration is about total fluid intake — from beverages and foods — and not just how many glasses of water you drink.

When Hydration Really Matters

While your body has a remarkable ability to regulate hydration and signal when it needs more fluid, certain populations must pay closer attention. Athletes, people working in hot climates, the elderly, and those who are ill may not feel thirst as readily — or may lose fluids faster than they can replenish them.

For these groups, choosing the right beverage matters. Water is still essential, but supplementing with drinks that contain electrolytes, some calories, and small amounts of protein or fat (like milk or specialized sports drinks) may offer superior hydration benefits.
Final Thoughts: Hydration is Personal

Hydration isn’t just about drinking the most water — it’s about how well your body retains and uses the fluids you consume. Milk proves to be a powerful hydrator thanks to its nutritional content, while drinks like coffee and even beer can contribute to fluid intake in moderation.

The real takeaway is that hydration is nuanced. A wide range of beverages — when consumed sensibly — can support hydration. The best approach? Listen to your body, drink regularly, and choose beverages that not only quench your thirst but nourish you in the process.

And remember: when in doubt, that glass of milk might just be the hidden champion of hydration